Structural and magnetic properties of Fe2P-type R6TTe2 compounds (R = Tb, Dy, Ho, Er, T = Fe, Co, Ru): Magnetic properties and specific features of magnetic entropy change

Article abstract of DOI:10.1016/j.jssc.2017.10.023

The magnetic properties and magnetic entropy changes of the Fe₂P-type Ho₆FeTe₂, Ho₆CoTe₂, Er₆CoTe₂, Tb₆RuTe₂, Dy₆RuTe₂ and Ho₆

Full text of DOI:10.1016/j.jssc.2017.10.023

Journal of Solid State Chemistry 258 (2018) 201–211
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Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Structural and magnetic properties of Fe2P-type R6TTe2 compounds
(R = Tb, Dy, Ho, Er, T = Fe, Co, Ru): Magnetic properties
and specific features of magnetic entropy change
A.V. Morozkina,⁎, V.K. Genchela, A.V. Knotkoa,b, V.O. Yapaskurtc, Jinlei Yaod, S. Quezadoe,
S.K. Malike
a
Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992, Russia
Faculty of Materials Science, Moscow State University, Leninskie Gory, House 1, Building 73, GSP-1, Moscow 119991, Russia
Department of Petrology, Geological Faculty Moscow State University, Leninskie Gory, Moscow 119992, Russia
Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Mathematics and Physics, Suzhou University of
b
c
d
Science and Technology, Suzhou 215009, China
e
Departamento de Física, Universidade Federal do Rio Grande do Norte, Natal 59082-970, Brazil
A R T I C L E I N F O
A B S T R A C T
Keywords:
The magnetic properties and magnetic entropy changes of the Fe2P-type Ho6FeTe2, Ho6CoTe2, Er6CoTe2,
Tb6RuTe2, Dy6RuTe2 and Ho6RuTe2 (space group P-62m, N 189, hP9) have been studied by means of bulk
magnetization and heat capacity measurements. Also, the tentative magnetic entropy change ΔSm* = (∂M / ∂T) × H
was used for characterization of magnetic ordering.
Ho6FeTe2, Ho6CoTe2, Er6CoTe2, Tb6RuTe2, Dy6RuTe2 and Ho6RuTe2 exhibit complex field sensitive ferro-
antiferromagnetic ordering. The correlation between the isothermal magnetic entropy change and the magnetic
ordering of these compounds have been studied.
Rare earth compounds
Magnetic properties
Magnetocaloric effect
Heat capacity
Magnetic entropy change
1. Introduction
viewed as one of the variants for the magnetic property modification of
the initial rare earths.
Intermetallic compounds composed of rare earth, transition metal
and p-elements are being actively studied for the occurrence of large
magnetocaloric effect over suitable temperature ranges for applications
in magnetic refrigeration/heating technologies and for the occurrence
of giant coercive force as potential basis for permanent magnets.
Meanwhile, it is necessary to know specific features of crystal structure
and magnetic properties of rare earth compounds in details to reach an
optimum of their magnetic properties.
The Tb6RuTe2 [1], Dy6RuTe2 [1–3], Ho6RuTe2 [1–3], Ho6FeTe2
[1,2,4], Ho6CoTe2 and Er6CoTe2 [1,2,5] compounds belong to the
family of Fe2P-type R6TX2 rare earth compounds (R = Sc, Y, Gd – Tm,
T = Mn, Fe, Co, Ni, Ru; X = Sb, Bi, Te; space group P-62m, No. 189,
hP9) [1–16].
These compounds are formed by a diffusion method and from
structural point of view they are ordered variant of Mg-type rare earth
based solid solutions: transition metal T and p-element X are inserted
into Mg-type rare earth lattice R with formation of Fe2P-type R6TX2
compounds with anisotropic distortion of initial Mg-type rare earth
lattice as shown in Ref. [3]. Thus, Fe2P-type R6TX2 compounds may be
The distortion of Mg-type sublattice by the transition metal and p-
element leads to considerable change of magnetic ordering of the rare
earth sublattice in the resulting R6TX2 compounds. The magnetic
ordering of transition metal sublattice T was not detected via neutron
diffraction study in zero applied field in R6TX2 compounds [3–5,12–16],
meanwhile Mn-containing compounds exhibit strong increase in tem-
perature of magnetic ordering in comparison with Fe-, Co-, Ni- and Ru-
containing R6TX2 compounds. Ho6FeBi2 and Ho6CoBi2 show Curie
temperatures of 54 K and 70 K, respectively, whereas Curie temperature
of Ho6MnBi2 is 200 K [3,13]. The compounds Ho6RuTe2, Ho6FeTe2 and
Ho6CoTe2 exhibit magnetic ordering at 11 K, 24 K and 60 K, respectively,
while Ho6MnTe2 show magnetic ordering at TC = 153 K [3–5,17]. These
results suggest that the magnetic ordering of Mn sublattice facilitates the
magnetic ordering of rare earth sublattice in the R6TX2 compounds.
Thus, Fe2P-type R6TX2 compounds and their solid solutions permit
one to engineer magnetic material with different magnetic ordering
temperatures over a large temperature range and the magnetic entropy
change indicates the magnetocaloric effect and field induced transfor-
mation of magnetic ordering of rare earth compounds.
⁎
Corresponding author.
E-mail address: morozkin@tech.chem.msu.ru (A.V. Morozkin).
http://dx.doi.org/10.1016/j.jssc.2017.10.023
Received 3 July 2017; Received in revised form 5 September 2017; Accepted 16 October 2017
Available online 16 October 2017
0022-4596/ © 2017 Elsevier Inc. All rights reserved.

A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
To understand variants ordering of rare earth sublattice and
magnetic field-induced transitions in Fe2P-type compounds and to
understand the role of magnetic entropy change for characterization of
magnetic ordering, the magnetic properties, magnetocaloric effect, heat
capacity and magnetic entropy change of Ho6FeTe2, Ho6CoTe2,
Er6CoTe2 and {Tb, Dy, Ho}6RuTe2 compounds have been investigated
in this work.
different temperatures to obtain magnetization in field of 140 kOe
(M140 kOe), remanent magnetization (Mres), critical (Hcrit) and coercive
fields (Hcoer). Magnetization isotherms were obtained at various
temperatures with a temperature step of 5 K (or 4 K) and a field step
of 2.5 kOe to calculate isothermal magnetic entropy changes (ΔSm).
3. Theory and calculations
The unit cell data were derived from powder XRD using the Rietan-
program [18,19] in the isotropic approximation at room temperature.
Bilbao Crystallographic server [20] was used for analysis of Fe2P-type
structure [2] according to the symmetry tables of the International
Tables of crystallography [21]. The paramagnetic susceptibility was
fitted to the Curie-Weiss law, yielding the effective magnetic moments
and paramagnetic Weiss temperatures [22]. Magnetic field (H),
coercive field (Hcoer) and critical field (Hcrit) are given in Oe unit
(1 Oe = 103/4π A/m and magnetic field of 1 Oe corresponds to the
strength of a magnetic field of 10−4 T). Magnetization is given in emu/g
and μB units (1 emu/g = 1 A m2/kg, 1 μB = 9.7400968(20)·10–24 A m2)
[22].
Magnetocaloric effect (MCE) is calculated in terms of the isother-
mal magnetic entropy change, ΔSm, using the magnetization vs field
data obtained near the magnetic transition using the thermodynamic
Maxwell relation [23]. The relative cooling power in field change 0–
50 kOe (RCP50 kOe) is calculated by multiplying of maximum of the
ΔSm by the full ΔT width at half maximum of ΔSm. The tentative
magnetic entropy change ΔSm* was calculated as ΔSm* = (∂M / ∂T) × H
from magnetization vs temperature in field of 100 Oe and 5 kOe (here
H the applied magnetic field, T the temperature and M the magnetiza-
tion) [24]. The tentative magnetic entropy change ΔSm* is same to
magnetic entropy change ΔSm at permanent ∂M / ∂T in different
applied magnetic fields and ΔSm* permits to understand type of
magnetic ordering. Electronic heat capacity coefficient γ of Er6CoTe2
was calculated by the expression CP / T = γ + β·T2 [22] above the
magnetic ordering temperature.
2. Experimental details
The Ho6FeTe2, Ho6CoTe2, Er6CoTe2 and {Tb, Dy, Ho}6RuTe2 alloys
were prepared by arc-furnace melting of stoichiometric amounts of rare
earth (99.9 wt%), Fe, Co and Ru (99.95 wt%) and Te (99.99 wt%) with
some surplus tellurium for compensation of the weight loss. The
samples were annealed at 1070 K for 240 h in an argon atmosphere
and subsequently quenched in ice-cold water. The quality of the
samples was evaluated using powder X-ray diffraction and microprobe
analyses. The X-ray data were obtained on a Rigaku D/MAX-2500
diffractometers (Cu Kα radiation, 2θ = 10–80° and 2θ = 5–120°, step
0.02). An INCA-Energy-350 X-ray EDS spectrometer (Oxford
Instruments) on the Jeol JSM-6480LV scanning electron microscope
(20 kV accelerating voltage, beam current 0.7 nA and beam diameter
50 µm) was employed to perform the microprobe analysis of the
sample. Signals averaged over three points per phase estimated
standard deviations of 1 at% for rare earth (measured by L-series
lines), 1 at% for iron, cobalt, ruthenium and tellurium (measured by K-
series lines).
Magnetization measurements of bulk polycrystalline Ho6{Fe, Co}
Te2, Er6CoTe2 and {Tb, Dy, Ho}6RuTe2 were carried out using a
vibrating sample magnetometer (VSM attachment on PPMS
Dynacool System, USA) in the temperature range of 2–300 K and in
magnetic fields up to 140 kOe. Specific heat measurements were
performed using relaxation method in PPMS. Low field (100 Oe)
magnetization data were obtained in zero-field-cooled (zfc) and field-
cooled (fc) states to determine the magnetic ordering temperatures.
The Curie temperature (TC) was defined as the dM/dT minima, and
Néel temperature (TN) was defined as M maximum. The temperature of
transformation of the magnetic ordering Tm or spin-reorientation
transition TSR was defined as local dM/dT minima or M maximum of
the thermal magnetization curve. Magnetization as a function of
temperature was measured in 5 kOe field in zero-field-cooled state to
obtain effective paramagnetic moment and paramagnetic Weiss tem-
perature. Magnetization vs field hysteresis curves were recorded at
4. Results
4.1. Quality of R6TX2 samples and unit cell data of Fe2P-type
compounds
The X-ray powder analyses showed that the Ho6{Fe, Co}Te2, Er6CoTe2
and {Tb, Dy, Ho}6RuTe2 compounds crystallize in the Fe2P-type structure
Table 1
Unit cell data of Fe2P-type R6TTe2 (R = Tb, Ho, Er, T = Fe, Co, Ru), space group P-62m, N 189, hP9, Z = 1, atomic positions: R1 3g [xR1, 0, 1/2], R2 3f [xR2, 0, 0], T 1b [0, 0, 1/2], Te 2c
[1/3, 2/3, 0].
N
1
2
3
4
5
6
Compound
a (nm)
c (nm)
c/a
V (nm3)
xR1
xR2
RF (%)
5.0
Ref.
a
Tb6RuTe2
Tb6RuTe2
Dy6RuTe2
Dy6RuTe2
Ho6RuTe2
Ho6RuTe2
Ho6FeTe2
Ho6FeTe2
Ho6CoTe2
Ho6CoTe2
Er6CoTe2
Er6CoTe2
0.82973(4)
0.82979
0.82515(5)
0.82449
0.82193(3)
0.82106
0.82017(4)
0.81894
0.82348(2)
0.82328
0.81975(4)
0.81955
0.40162(2)
0.40162
0.40077(2)
0.40049
0.39982(2)
0.39943
0.40003(2)
0.39939
0.39360(1)
0.39352
0.39239(2)
0.39232
0.48404
0.48400
0.48569
0.48574
0.48644
0.48648
0.48774
0.48769
0.47797
0.47799
0.47867
0.47870
0.23945
0.23949
0.23632
0.23577
0.23392
0.23320
0.23304
0.23197
0.23115
0.23099
0.22836
0.22820
0.5970(4)
0.5971
0.5971(5)
0.5978
0.6011(3)
0.6015
0.6000(5)
0.5997
0.6000(3)
0.6001
0.5985(4)
0.5981
0.2421(4)
0.2426
0.2442(4)
0.2430
0.2424(3)
0.2419
0.2379(4)
0.2386
0.2379(3)
0.2376
0.2365(4)
0.2375
[1]b
a
5.3
[1]c
a
2.6
[1]d
a
4.3
[1]e
a
3.4
[1]f
a
2.9
[1]g
a
b
c
d
e
f
This work.
Tb6RuTe2 [1] PDF#00-066-0505.
Dy6RuTe2 [1] PDF#00-060-00176.
Ho6RuTe2 [1] PDF#00-060-00169.
Ho6FeTe2 [1] PDF#00-060-00172.
Ho6CoTe2 [1] PDF#00-059-90324.
Er6CoTe2 [1] PDF#00-061-10126.
g
202

A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 2. Magnetization as a function of temperature in field of 100 Oe of (a) Tb6RuTe2, (b)
Dy6RuTe2 and (c) Ho6RuTe2.
Fig. 1. Magnetization as a function of temperature in field of 100 Oe of (a) Ho6FeTe2, (b)
Ho6CoTe2 and (c) Er6CoTe2.
reports [4,5] (Fig. 1). The compound Ho6FeTe2 orders antiferromag-
(space group P-62m, N 189, hP9), and the EDS spectra revealed the
composition of R67(1)T10(1)Te23(1) for the R6TTe2 samples. The refined unit
cell data and atomic positions are given in Table 1, They are in good
agreement with the previously reported unit cell data of these compounds
[1]. From X-ray powder analysis, Ho6{Fe, Co}Te2, Er6CoTe2 and {Dy,
Ho}6RuTe2 samples contain around 1–3 wt% of NaCl-type RTe com-
netically at TN = 27 K and shows a ferromagnetic-like transition at TC
=
8 K (Fig. 1a). The antiferromagnetic transition corresponds to the
transformation of paramagnet into flat ab-plane antiferromagnetic flat
spiral, whereas ferromagnetic transition indicates the transformation
of antiferromagnetic flat spiral into c-axis ferromagnetic cone [4].
The Ho6CoTe2 and Er6CoTe2 exhibit dominant ferromagnetic order
at TC = 63 K and TC = 31 K, respectively (Fig. 1b and c). The ordered
state corresponds to the c-axis ferromagnetic and ab-antiferromagnetic
order in Ho6CoTe2 (set of c-ferromagnetic cones) and ab-plane
ferromagnetic-antiferromagnetic order of Er6CoTe2 [5]. The maximum
of magnetization curve at TSR = 25 K indicates change of Ho6CoTe2
magnetic ordering: additional ab-plane ferromagnetic component
transforms the c-ferromagnetic cones into set of non-collinear ferro-
magnetic cones as shown in [5].
In a field of 100 Oe, Ho6RuTe2 shows antiferromagnetic ordering at
TN = 11 K (this work and [3,17]), whereas Tb6RuTe2 and Dy6RuTe2
exhibit ferromagnetic-like ordering at TC = 135 K and TC = 64 K,
respectively (Fig. 2). Tb6RuTe2 and Dy6RuTe2 show further transfor-
mations of magnetic ordering at Tm = 75 K and TN = 30 K for Tb6RuTe2
and Tm1 = 28 K and Tm2 = 15 K for Dy6RuTe2. The anomaly in the
magnetization curve of Tb6RuTe2 at Tm = 75 K differs from Néel point
of TbTe (TN = 63 K) [2] and it may correspond to the intrinsic magnetic
order of the Tb6RuTe2 compound.
pounds ('R50(2)Te50(3)' phases from microprobe analysis), whereas
Tb6RuTe2 sample contains 12 wt% of NaCl-type TbTe [2]. Therefore the
NaCl-type antiferromagnets TbTe (TN = 63 K), DyTe (TN ~ 40 K), HoTe
(TN = 20 K) and ErTe (TN ~ 10 K) [2,25,26] may influence the
magnetization measurements. However, it can be neglected for Ho6{Fe,
Co}Te2, Er6CoTe2 and {Dy, Ho}6RuTe2 as the quantity of admixture phase
is close to estimated standard deviation (ESD) of magnetic measurements,
whereas it has to be considered for Tb6RuTe2. Thus, a priori, while the
measured magnetic properties of Ho6{Fe, Co}Te2, Er6CoTe2 and {Dy,
Ho}6RuTe2 samples correspond to the properties of single phase bulk
polycrystalline alloys, the magnetic properties of Tb6RuTe2 will be only
tentative, considering the secondary phase.
4.2. Magnetic transitions
In applied field of 100 Oe, Ho6FeTe2, Ho6CoTe2 and Er6CoTe2
exhibit magnetic transitions in complete accordance with the previous
203

A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 4. Magnetization vs temperature of (a) Tb6RuTe2, (b) Dy6RuTe2 and (c) Ho6RuTe2
in field of 5 kOe (paramagnetic susceptibily vs temperature inserted into figures).
Fig. 3. Magnetization vs temperature of (a) Ho6FeTe2, (b) Ho6CoTe2 and (c) Er6CoTe2 in
field of 5 kOe (paramagnetic susceptibily vs temperature inserted into figures).
ture range of ~ 200–300 K, ~ 150–300 K and ~ 70–300 K, respec-
tively. The fit to the Curie-Weiss law yields paramagnetic Weiss
temperatures Θp = 61 K for Tb6RuTe2, Θp = 18 K for Dy6RuTe2 and
Θp = −0.6 K for Ho6RuTe2, suggesting dominant ferromagnetic inter-
actions in Tb6RuTe2 and Dy6RuTe2 and weak antiferromagnetic
interaction in Ho6RuTe2 (Fig. 4). The effective moments per formula
unit, Meff/fu, are 24.1 μB for Tb6RuTe2, 26.1 μB for Dy6RuTe2 and
26.0 μB for Ho6RuTe2 suggest the effective magnetic moments per rare
earth, Meff / R, of 9.83 μB, 10.66 μB and 10.61 μB for Tb6RuTe2,
Dy6RuTe2 and Ho6RuTe2, respectively (theoretical effective magnetic
moments are 9.72 μB for Tb, 10.65 μB for Dy and 10.61 μB for Ho [27]).
4.3. Paramagnetic susceptibility
In a field of 5 kOe, the paramagnetic susceptibility of Ho6FeTe2,
Ho6CoTe2 and Er6CoTe2 follows the Curie-Weiss law in the tempera-
ture range of ~ 130–300 K, ~ 170–300 K and ~ 100–300 K, respec-
tively. The fit to the Curie-Weiss law yields positive paramagnetic
Weiss temperatures Θp = 49 K for Ho6FeTe2, Θp = 67 K for Ho6CoTe2
and Θp = 21 K for Er6CoTe2, suggesting dominant ferromagnetic
interactions (Fig. 3). The effective moments per formula unit, Meff
/
fu, are 26.0 μB for both Ho6FeTe2 and Ho6CoTe2 and 23.5 μB for
Er6CoTe2. This suggests effective magnetic moments per Fe of 0.8 μB in
Ho6FeTe2 and effective magnetic moment per Co of 0.8 μB and 1.3 μB
in Ho6CoTe2 and Er6CoTe2, respectively, assuming that Ho and Er take
the theoretical effective magnetic moment values of 10.61 μB and
9.58 μB, respectively [27]. These values hint that the itinerant electrons
of Fe and Co sublattice do play a role in deciding the magnetic
properties of these R6TX2 compounds (the theoretical iron and cobalt
effective magnetic moment of 2.216 μB and 1.715 μB, respectively
[27]).
4.4. Magnetization
The magnetization vs magnetic field data of Ho6FeTe2, Ho6CoTe2,
Er6CoTe2, Tb6RuTe2, Dy6RuTe2 and Ho6RuTe2 at 2 K are plotted in
Figs. 5 and 6.
Ho6FeTe2 is soft ferromagnet with zero residual magnetization and
coercive field. At 2 K, the magnetization per holmium of Ho6FeTe2 in
field of 140 kOe (M140 kOe / R) reaches value of 7.9 μB (saturation
magnetization per holmium M∞ / R → 8.6 μB at 1/H → 0). These values
indicate the near- collinear ordering of holmium sublattice at 2 K and
140 kOe (the theoretical Ho magnetic moment of 10 μB [27]).
In a field of 5 kOe, the paramagnetic susceptibility of Tb6RuTe2,
Dy6RuTe2 and Ho6RuTe2 follows the Curie-Weiss law in the tempera-
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A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 6. Magnetization vs magnetic field from −140 to 140 kOe of (a) Tb6RuTe2, (b)
Dy6RuTe2 and (c) Ho6RuTe2 at 2 K.
Fig. 5. Magnetization vs magnetic field from −140 to 140 kOe of (a) Ho6FeTe2, (b)
9 kOe of Tb6RuTe2 are followed by the significant hysteresis in applied
magnetic fields above ~ 3 kOe with critical field Hcrit of 16 kOe. The
magnetization per terbium of Tb6RuTe2 in field of 140 kOe (M140 kOe / R)
reaches value of 6.6 μB (saturation magnetization per terbium M∞ / R →
8.7 μB at 1/H → 0). The specific features of Tb6RuTe2 magnetization
suggests no significant role of antiferromagnetic admixture TbTe of ~
12 wt%. Perhaps, Tb6RuTe2 has complex ferromagnetic cone with
magnetic structure at 2 K, similar to Ho6FeTe2 compound.
At 2 K, Dy6RuTe2 shows hysteresis, with residual magnetization per
rare earth Mres / R of 3.7 μB, coercive field Hcoer of 5.3 kOe and critical
field of Hcrit ~ 2 kOe (Fig. 6b). The magnetic moment per rare earth in
field of 140 kOe (M140 kOe / R) is about 6.4 μB (M∞ / R = 7.7 μB),
indicating a noncollinear order of the Dy sublattice in Dy6RuTe2 (the
theoretical magnetic moment of Dy is 10 μB [27]).
Ho6CoTe2 and (c) Er6CoTe2 at 2 K.
Ho6FeTe2 exhibits field induced magnetization hysteresis above critical
field of Hcrit ~ 2 kOe at 2 K (Fig. 5a). From neutron diffraction study in
zero applied field, ferromagnetic component per holmium reaches
values of ~ 3 μB at 2 K [4]. Thus, magnetization Ho6FeTe2 at 2 K shows
field induced transformation of ferromagnetic cone with increasing
resulting ferromagnetic component.
Ho6CoTe2 and Er6CoTe2 show permanent magnet properties with
residual magnetization per rare earth Mres / R of 6.5 μB and 6.9 μB,
respectively and with coercive field of 1.7 kOe for Ho6CoTe2 and
1.6 kOe for Er6CoTe2 (Fig. 5b and c). The magnetization per rare earth
in field of 140 kOe (M140 kOe / R) reaches value of 8.5 μB for Ho6CoTe2
(M∞ / R = 9.2 μB) and 7.1 μB for Er6CoTe2 (M∞ / R = 8.3 μB). From
neutron diffraction study in zero applied field, ferromagnetic compo-
nent per rare earth reaches values of ~ 5 μB in Ho6CoTe2 and ~ 6 μB in
Er6CoTe2 at 2 K [5] and applied magnetic field transforms ferro-
antiferromagnets into near-collinear ferromagnets.
Above critical field Hcrit of 5 kOe at 2 K, Ho6RuTe2 is a soft
ferromagnet with the magnetization per holmium M140 kOe / R of
7.7 μB in field of 140 kOe (saturation magnetization per holmium M∞
/
R → 9.2 μB at 1/H → 0). These values indicate near-collinear field
induced ordering of holmium sublattice (the theoretical Ho magnetic
moment of 10 μB [27]). Perhaps, in zero applied field magnetic
structure of Ho6RuTe2 is ab-flat spiral as the high-temperature
magnetic structure of Ho6FeTe2 [4].
The magnetization vs field of Tb6RuTe2 is similar to one of Ho6FeTe2
(see Figs. 5a and 6a). At 2 K, the insignificant Mres/fu ~ 2.3 μB and Hcoer
~
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A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 7. Temperature dependence of the specific heat CP of Er6CoTe2: γ is fitted from
expression CP/T = γ + βT2 (38–50 K) (CP/T vs. T2 inserted into figure).
4.5. Specific heat of Er6CoTe2
The heat capacity of Er6CoTe2 shows Debye temperature TD of 140 K,
at which heat capacity reaches value of 230.7 J/mol K corresponding to
the theoretical heat capacity of 3 R/atom (here R the universal gas
constant [27]) (Fig. 7). The specific heat shows a sharp peak at ~ 29 K,
indicating a ferromagnetic ordering of Er6CoTe2. The electronic heat
capacity coefficient of γ of 1.9 J/(mol K2) is obtained by fitting the low
temperature data. Although higher than ~ 29 K the magnon specific heat
may be neglected, fit to the Cp/T − T2 from 38 to 58 K yields the negligible
phonon coefficient. The enthalpy change ΔHm of 210 J/mol corresponds
to the magnetic ordering of Er6CoTe2 at TC = 31 K.
4.6. Magnetocaloric effect (MCE) and magnetic entropy change
The magnetocaloric effects of Ho6FeTe2, Ho6CoTe2, Er6CoTe2,
Tb6RuTe2, Dy6RuTe2 and Ho6RuTe2 were calculated in terms of the
isothermal magnetic entropy change, ΔSm, from the magnetization vs
field data (Figs. 1s and 2s). The tentative isothermal magnetic entropy
change, ΔSm*, was estimated from the magnetization vs temperature
data in field of 100 Oe (zfc and fc curves) (Figs. 1 and 2) and in field of
5 kOe (Figs. 3 and 4).
4.6.1. Ho6FeTe2
Fig. 8. Ho6FeTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
The tentative magnetic entropy change ΔSm* of Ho6FeTe2 calcu-
lated from magnetization vs temperature in field of 100 Oe (see Fig. 1a)
and it indicates field induced ferromagnetic transition around 30 K
followed by the antiferromagnetic transition at 24 K and low-tempera-
ture ferromagnetic ordering at 7 K (Fig. 8a). The transitions at 24 K
corresponds to the ab-flat spiral antiferromagnetic ordering, whereas
transition at 30 K indicates partially metamagnetic transition of ab-flat
spiral into c-ferromagnetic cone in Ho6FeTe2 [4].
The tentative magnetic entropy change ΔSm* of Ho6FeTe2 calcu-
lated from magnetization vs temperature in field of 5 kOe (see Fig. 3a)
exhibits ferromagnetic-like transformation of Ho6FeTe2 magnetic
ordering at 26 K (ΔSm* = −1.7 J/kg K) and 9 K (ΔSm* = −1.6 J/kg·K)
with positive magnetic entropy change below 9 K (Fig. 8a).
The tentative magnetic entropy change ΔSm* data are in full
accordance with magnetic entropy change ΔSm data in field change of
0–5 kOe with ΔSm = −1.6 J/kg K at 22 K, ΔSm = −1.3 J/kg K at 7 K and
positive magnetic entropy change below ~ 4 K (Fig. 8b).
The high-temperature and low-temperature magnetic entropy
changes correspond to the field induced metamagnetic transition and
low-temperature ferromagnetic ordering of Ho6FeTe2, respectively.
The low-temperature positive magnetic entropy change below ~ 7 K
indicates field induced antiferromagnetic transformation (this trans-
formation was not observed in zero applied field in neutron diffraction
study), which corresponds to the metamagnetic transition in field of ~
2 kOe and hysteresis of Ho6FeTe2 at 2 K (see inset in Fig. 5a).
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
The magnetic entropy change ΔSm of Ho6FeTe2 shows maximal
values of −12.9 J/kg K (relative cooling power RCP50 kOe ~ 650 J/kg) at
22 K and −6.2 J/kg K at 7 K for a field change 0–50 kOe and −21.6 J/
kg K at 22–52 K and −10.3 J/kg K at 7 K for a field change 0–140 kOe
(Figs. 8c and 3s).
max
The maximal magnetic entropy change ΔSm
at corresponding
temperatures vs magnetic field changes ΔH indicates quasi-linear
behaviour in field change 2.5–10 kOe and non-linear behaviour in
field change 2.5–140 kOe (insets in Fig. 8b and c). It attributes to the
transformation from initial antiferromagnetic cone of Ho6FeTe2 into
near-collinear ferromagnetic state in applied magnetic field at different
temperatures.
4.6.2. Ho6CoTe2
Tentative magnetic entropy change ΔSm* in field of 100 Oe and
5 kOe and magnetic entropy change ΔSm of Ho6CoTe2 for a field change
of 0–10 kOe and 0–50 kOe are given in Fig. 9.
The ΔSm* in field of 100 Oe shows ferromagnetic ordering and field
induced transformation of ferromagnetic cone into collinear ferromag-
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A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 10. Er6CoTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
Fig. 9. Ho6CoTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
zero applied field in neutron diffraction study), which corresponds to
the metamagnetic transition in field of 1.7 kOe and hysteresis of
Ho6CoTe2 at 2 K (see Fig. 5b).
netic state of Ho6CoTe2 at 61–53 K and a complex field induced
transformation of its magnetic structure at 16 K (the magnetic
structure of Ho6CoTe2 is set of non-collinear ferromagnetic cones
below TSR = 25 K in zero applied field [5]) (inset in Fig. 9a).
In a field of 5 kOe, ΔSm* of Ho6CoTe2 indicates high-temperature
and low-temperature ferromagnetic-like transitions at 62 K (ΔSm* =
−1.3 J/kg K) and 16 K (ΔSm* = −1.0 J/kg K) with positive magnetic
entropy change below ~ 6 K (Fig. 9a). These data are in good
accordance with magnetic entropy change ΔSm of −1.2 J/kg K at 60 K
and −0.9 J/kg K at 15 K, in field change 0–5 kOe (Fig. 9b).
The magnetic entropy change ΔSm of Ho6CoTe2 shows maximal
values of −11.5 J/kg K (RCP50 kOe ~ 520 J/kg) at 60 K and −6.6 J/kg K
at 15 K for a field change 0–50 kOe and −24.9 J/kg K at 60 K and
−12.9 J/kg K at 20 K for a field change 0–140 kOe (Figs. 9c and 3s).
max
The maximal magnetic entropy change ΔSm
at corresponding
temperatures vs magnetic field changes ΔH indicates linear behaviour
in field change 2.5–10 kOe and non-linear behaviour in field change
2.5–140 kOe (insets in Fig. 9b and c). It attributes to the transforma-
tion from initial ferro-antiferromagnet Ho6CoTe2 into collinear ferro-
magnetic state in applied magnetic field at different temperatures.
The high-temperature magnetic entropy change corresponds to the
field induced transformation from c-ferromagnetic cones of Ho6CoTe2
[5] into near-collinear c-ferromagnetic state at TC = 60 K and low-
temperature magnetic entropy change indicates ferromagnetic trans-
formation from non-collinear ferromagnetic cone of Ho6CoTe2 into
near-collinear ferromagnetic state around 15 K. The positive magnetic
entropy change below ~ 5 K corresponds to the field induced anti-
ferromagnetic transformation (this transformation was not observed in
4.6.3. Er6CoTe2
From neutron diffraction study in zero applied field Er6CoTe2
shows ab-plane ferro-antiferromagnetic ordering below TC = 30 K [5].
The ΔSm* in fields of 100 Oe and 5 kOe exhibits ferromagnetic
ordering of Er6CoTe2 at 30 K with ΔSm* = −1.9 J/kg K in field of 5 kOe
(Fig. 10a). This corresponds to the magnetic entropy change ΔSm of
−1.8 J/kg K at 30 K in field change 0–5 kOe (Fig. 10b). The low-
207

A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
The tentative magnetic entropy change ΔSm* of Tb6RuTe2 calculated
from magnetization vs temperature in field of 5 kOe (see Fig. 4a)
exhibits ferromagnetic-like transformation of magnetic ordering at
134 K (ΔSm*
antiferromagnetic ordering at 69 K (ΔSm* = + 0.02 J/kg K) and low-
temperature ferro-antiferromagnetic ordering at 33 K (ΔSm*
= −0.06 J/kg K) and 79 K (ΔSm* = −0.06 J/kg K),
=
−0.07 J/kg K) and 20 K (ΔSm* = + 0.34 J/kg K) (Fig. 11a). These data
are in full accordance with magnetic entropy change ΔSm data in field
change of 0–5 kOe: ΔSm = −0.08 J/kg K at 127 K, ΔSm = −0.03 J/kg K
at 72 K, ΔSm = + 0.03 J/kg K at 62 K, ΔSm = −0.04 J/kg K at 32 K and
ΔSm = + 0.27 J/kg K at 17 K (Fig. 11b). The positive magnetic entropy
change at 62 K corresponds to the antiferromagnetic ordering of 12 wt
% admixture TbTe (TN = 63 K) [2]. From magnetic entropy change we
may suggest the c-ferromagnetic ordering of Tb sublattice in Tb6RuTe2
at TC = 135 K, additional ab-plane flat spiral component at Tm = 75 K
(tentative magnetic structure of Tb6RuTe2 is set of c-collinear ferro-
magnetic cones) and transformation of magnetic ordering into e.g. set
of non-collinear ferromagnetic cones at TN = 30 K.
The magnetic entropy change ΔSm of Tb6RuTe2 shows maximal
values of −1.3 J/kg K at 127 K, −2.2 J/kg K at 72 K, −3.8 J/kg K at
27 K and + 10.0 J/kg K at 2 K for a field change 0–50 kOe and −11.8 J/
kg K at 77 K, −7.4 J/kg K at 27 K and + 27.7 J/kg K at 2 K for a field
change 0–140 kOe (Figs. 11c and 4s).
max
The maximal magnetic entropy change ΔSm
at corresponding
temperatures indicates almost linear behaviour vs magnetic field
changes ΔH (insets in Fig. 11b and c) and the low-temperature positive
magnetic entropy change indicates the antiferromagnetic transforma-
tion of Tb6RuTe2, which corresponds to the metamagnetic transition in
field of 16 kOe and hysteresis 2 K (see Fig. 6a).
4.6.5. Dy6RuTe2
Tentative magnetic entropy change ΔSm* in field of 100 Oe and
5 kOe (see Figs. 2b and 4b) and magnetic entropy change ΔSm for a
field change of 0–10 kOe and 0–50 kOe of Dy6RuTe2 are given in
Fig. 12.
The ΔSm* in a field of 100 Oe of Dy6RuTe2 shows ferromagnetic
ordering at 65 K and 25 K and field sensitive antiferromagnetic-like
transformation of magnetic ordering at 10 K (inset in Fig. 12a). In a
field of 5 kOe, the following ΔSm* value corresponds to these transi-
tions: ΔSm* = −0.1 J/kg K at 58 K, ΔSm* = −0.2 J/kg K and 26 K and
ΔSm* = + 0.44 J/kg K at 8 K (Fig. 12a). These data correspond to the
magnetic entropy change ΔSm in field change 0–5 kOe: ΔSm = −0.1 J/
kg K at 57 K, ΔSm = −0.18 J/kg K at 27 K and ΔSm = + 0.5 J/kg K at
2 K (Fig. 12b).
Fig. 11. Tb6RuTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
The magnetic entropy change ΔSm of Dy6RuTe2 shows maximal
values of −2.4 J/kg K at 57 K, −4.5 J/kg K at 22 K and + 4.2 J/kg K at
2 K for a field change 0–50 kOe and −12.8 J/kg K at 27 K and + 5.1 J/
temperature positive tentative magnetic entropy change ΔSm* and
magnetic entropy change ΔSm may correspond to field induced
antiferromagnetic transformation (this transformation was not ob-
served in zero applied field in neutron diffraction study), which
corresponds to the metamagnetic transition in field of 6.9 kOe and
hysteresis of Er6CoTe2 (see Fig. 5c).
The magnetic entropy change ΔSm of Er6CoTe2 shows maximal
value of −14.6 J/kg K (RCP50 kOe ~ 370 J/kg) at 30 K for a field change
0–50 kOe and −27.4 J/kg K at 30–34 K for a field change 0–140 kOe
kg K at 2 K for a field change 0–140 kOe (Figs. 12c and 4s).
max
The maximal magnetic entropy change ΔSm
at corresponding
temperatures indicates linear behaviour vs magnetic field changes ΔH
for the ferromagnetic-like transitions at TC = 64 K and Tm1 = 28 K and
saturated behaviour at Tm2 = 15 K (insets in Fig. 12b and c). The low-
temperature positive magnetic entropy change indicates the antiferro-
magnetic transformation of Dy6RuTe2 whith metamagnetic transition
in field of 25 kOe and hysteresis at 2 K (see Fig. 6b).
(Figs. 10c and 3s).
max
The maximal magnetic entropy change ΔSm
at corresponding
temperatures vs magnetic field changes ΔH indicates linear behaviour
in field change 2.5–10 kOe and non-linear behaviour in field change
2.5–140 kOe (insets in Fig. 10b and c). It is due to field induced
transformation of initial ferro-antiferromagnet Er6FeTe2.
4.6.6. Ho6RuTe2
The tentative magnetic entropy change ΔSm* of Ho6RuTe2 calcu-
lated from magnetization vs temperature in a field of 100 Oe (see
Fig. 2c) shows ferromagnetic-like transition at 15 K followed by the
antiferromagnetic-like transition at 8 K (inset in Fig. 13a). The ΔSm* in
5 kOe exhibits ferromagnetic-like transformation of Ho6RuTe2 at 14 K
(ΔSm* = −0.36 J/kg K) with antiferromagnetic ordering and positive
magnetic entropy change below 6 K (ΔSm* = + 1.0 J/kg K) (Fig. 13a).
This indicates metamagnetic transformation of antiferromagnetic
ordering as the ab-flat spiral ordering suggested for Ho6RuTe2, like
4.6.4. Tb6RuTe2
The tentative magnetic entropy change ΔSm* calculated from
magnetization vs temperature in field of 100 Oe (see Fig. 2a) indicates
ferromagnetic ordering of Tb6RuTe2 at 134 K followed by transforma-
tion of magnetic ordering at 78 K, 30 K and 24 K (inset in Fig. 11a).
208

A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
Fig. 12. Dy6RuTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
Fig. 13. Ho6RuTe2: (a) tentative magnetic entropy change, -ΔSm* vs temperature in field
of 5 kOe and magnetic entropy change -ΔSm in field changes of (b) 0–10 kOe and (c) 0–
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
50 kOe. Tentative magnetic entropy change, -ΔSm* vs temperature in field of 100 Oe
max
inserted into figure (a). Maximal values of magnetic entropy change -ΔSm
corresponding temperatures vs field change ΔH inserted into figures (b) and (c).
at
high-temperature antiferromagnetic order of Ho6FeTe2 [4]. The tenta-
tive magnetic entropy change ΔSm* data are in full accordance with
magnetic entropy change ΔSm data in field change of 0–5 kOe with ΔSm
= −0.27 J/kg K at 14 K and ΔSm = + 0.5 J/kg K at 6 K (Fig. 13b).
The magnetic entropy change ΔSm shows the transformation from
initial antiferromagnet into ferromagnet with ΔSm of −10.0 J/kg K
(RCP50 kOe ~ 300 J/kg) at 10 K for a field change 0–50 kOe and
−22.8 J/kg K at 14–18 K for a field change 0–140 kOe (Figs. 13c and
4s), whereas low-temperature peaks with positive ΔSm is suppressed
(see insets in Fig. 13b and c with ΔSm vs field change ΔH).
tices as shown in Fig. 5s. These modifications of Fe2P-type lattice may
be observed in solid solution based on the R6TX2 compounds, which
may be obtained at various synthesis conditions or be due to structural
transformation of of Fe2P-type lattice at different temperatures.
Certainly, the types of transition metal and p-element permit to
modify magnetic ordering of initial Mg-type rare earth lattice in the
resulting magnetic ordering of R6TX2 compounds in width range,
including temperature and type of magnetic ordering as shown in Ref. [3].
In this work the magnetic properties of Ho6FeTe2, Ho6CoTe2,
Er6CoTe2, {Tb, Dy, Ho}6RuTe2 were investigated in details. As shown
in this work, the magnetic entropy change shows thermal and field
induced transformation of magnetic ordering of the R6TX2 compounds
that may be background for optimization of magnetic properties of rare
earth compounds.
The obtained magnetic data for Ho6FeTe2, Ho6CoTe2, Er6CoTe2,
{Tb, Dy, Ho}6RuTe2 are summarized in Table 2.
5. Discussion
The comparison between tentative magnetic entropy change and
magnetic entropy change measured by a standard method [23] are in
good agreement. Certainly, the tentative magnetic entropy change supple-
ments the standard magnetic entropy change, only. Meanwhile, it can be
used for tentative calculation of magnetocaloric effect at linear or local
linear dependence ΔSm maximal values vs magnetic field change.
As shown in Bilbao Crystallographic Server [20], P-62m space
group may be given in trigonal P31m, P321, hexagonal P-6 and
orthorhombic Amm2 maximal subgroups. The Fe2P-type R6TX2 unit
cell (type structure) may be given in term of these groups with
transformation of rare earth, transition metal and p-element sublat-
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Journal of Solid State Chemistry 258 (2018) 201–211
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A.V. Morozkin et al.
Journal of Solid State Chemistry 258 (2018) 201–211
00169; Ho6FeTe2 PDF#00-060-00172; Ho6CoTe2 PDF#00-059-90324; Er6CoTe2
PDF#00-061-10126.
6. Conclusion
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The parent Mg-type rare-earth metal could effectively be altered
and used to synthesize novel materials of Fe2P-type structure whith
varying magnetic properties over a broad range of temperatures. Those
magnetic transitions eventually could lead to interesting and functional
physical properties.
The tentative magnetic entropy change obtained from magnetiza-
tion vs temperature in different magnetic fields is useful instrument for
calculation of tentative magnetocaloric effect and understanding the
type of magnetic ordering in these compounds.
[9] A.V. Morozkin, J. Alloy. Compd. 358 (2003) L9–L10.
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[17] S.K. Malik, S. Quezado, A.V. Morozkin, R. Nirmala, Magnetocaloric Effect in
Ho6RuX2 (X = Te, Sb and Bi) Compounds (In press).
Acknowledgments
This work is supported by Russian Fund for Basic Research
through the project No. 16-03-00666-a and the National Natural
Science Foundation of China (Grant No. 51301116), the 333 Project,
the Six-Summit Project of Jiangsu (Grant No. 2013-XCL-038). SKM
acknowledges partial financial support from MEC-UFRN (Brazil). The
unit cell data of Ho6{Fe, Co}Te2, Er6CoTe2 and {Tb, Dy, Ho}6RuTe2
used with permission – ©JCPDS – International Centre for Diffraction
Data. A.V. Knotko acknowledge partial support from M.V. Lomonosov
Moscow State University Program of Development. Thanks to R.
Nirmala (Indian Institute of Technology Madras, Chennai 600036,
India) for useful comments.
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Institute of Physics Publishing, Bristol, Philadelphia, 2003, p. 480.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found in the
online version at doi:10.1016/j.jssc.2017.10.023.
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References
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211