Structure and magnetostriction of Ho 1 -xPrx Fe 1.9 alloys

Article abstract of DOI:10.1016/j.jmmm.2011.12.023

Polycrystalline Ho1_-x^PrxFe1.9 (0≤x≤1) cubic Laves alloys were synthesized by arc-melting and subsequent annealing under high stress. Their structure, magnetic properties and magnetostriction are investigated using X-ray diffraction, vibrating sample magnetometer and standard strain gauge technique, respectively. It was found that Ho1_-x^PrxFe1.9 single cubic Laves phase cannot be obtained when x>0.2 by a traditional vacuum annealing method. In contrast, the cubic Laves phase can be stabilized over the whole studies range in the samples annealed under high stress. The saturation magnetization for Ho1_-x^PrxFe1.9 decreases with the increase of x and reaches a minimum at x=0.4, then increases with further increase of x, which indicates the antiparallel magnetic moment alignment between Ho and Pr sublattice. The magnetostriction of Ho1_-x^{Prx Fe1.9} does not linearly increase with increasing x, but presents a minimum at x=0.4.

Full text of DOI:10.1016/j.jmmm.2011.12.023

Journal of Magnetism and Magnetic Materials 324 (2012) 1627–1630
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Journal of Magnetism and Magnetic Materials
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Structure and magnetostriction of Ho1 Pr Fe alloys
ꢀx
a
x
1:9
a,n
b
b
a
b
b
Y.G. Shi , L. Zhai , Y. Wang , J.Y. Fan , D.N. Shi , S.L. Tang , Y.W. Du
a
Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
b
National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Polycrystalline Ho1 Pr Fe
1:9
ð0rxr1Þ cubic Laves alloys were synthesized by arc-melting and
ꢀx
x
Received 2 May 2011
Received in revised form
subsequent annealing under high stress. Their structure, magnetic properties and magnetostriction
are investigated using X-ray diffraction, vibrating sample magnetometer and standard strain gauge
3
0 November 2011
x
technique, respectively. It was found that Ho1ꢀxPr Fe1:9 single cubic Laves phase cannot be obtained
when x40:2 by a traditional vacuum annealing method. In contrast, the cubic Laves phase can be
Available online 19 December 2011
Keywords:
stabilized over the whole studies range in the samples annealed under high stress. The saturation
Cubic Laves phase
Magnetic property
Magnetostriction
magnetization for Ho1ꢀxPr
increases with further increase of x, which indicates the antiparallel magnetic moment alignment
x
Fe1:9 decreases with the increase of x and reaches a minimum at x¼0.4, then
between Ho and Pr sublattice. The magnetostriction of Ho1ꢀxPr
x
Fe1:9 does not linearly increase with
increasing x, but presents a minimum at x ¼ 0:4.
&
2011 Elsevier B.V. All rights reserved.
1
. Introduction
Laves phase. But the single cubic Laves could not be obtained in
0:1 alloys when the Pr concentration exceeds
40 at% in rare-earth sublattice [6]. A similar result was also
reported by Hari Babu et al. [7]. Up to present, Ho1ꢀxPr Fe cubic
x
Tb0:1Ho0:9ꢀxPr Fe0:9B
RFe
extensively investigated due to their giant magnetostriciton at
room temperature. Terfenol-D (Tb0.27Dy0.73Fe ), with low mag-
2
(R¼rare earths) C15 cubic Laves phase alloys were
x
2
2
Laves alloys have not yet been synthesized and their magnetic
netic anisotropy and large low-field magnetostriction, has been
widely applied in sonar transducer, sensors, actuators, etc. [1,2].
However, the raw materials of Terfenol-D are mainly expensive
heavy rare earths Tb and Dy. According to the single-ion model,
properties remain unknown. Recently, we reported that the
structure and magnetic properties of PrFe
x
ð1:5rxr3Þ alloys
synthesized by annealing as-cast ingots under 6 GPa and the
single cubic Laves phase was realized in PrFe1.9 [8]. In this paper,
PrFe
than TbFe
factor
2
possesses a larger calculated magnetostriction constant
polycrystalline alloys Ho1ꢀxPr Fe1:9 ð0rxr1Þ with cubic Laves
x
2
and DyFe at 0 K due to its large second-order Stevens’
2
phase have been successfully synthesized by the same method.
The crystal structure, magnetic properties and the magnetostric-
tion of the alloys are investigated.
a
J
, ground state angular momentum J and average radius
2
3þ
/
r
S of the 4f electron shell of the Pr
ion [1]. In addition, a
4f
magnetostrictive material with high-Pr content should have a
good practical prospect because it is much cheaper than the
heavy rare earths Tb or Dy. However, former studies showed that
2. Experiment
2
PrFe cubic Laves phase could not be synthesized by conventional
Ingots with Ho1ꢀxPr Fe1:9 (x ¼ 0:0, 0.2, 0.4, 0.6, 0.8 and 1.0)
x
annealing at ambient pressure [3]. The unwanted non-cubic
phase appears and the single phase materials cannot be synthe-
stoichiometry were prepared by melting the appropriate consti-
tuent metals in a magneto-controlled arc furnace under a high-
purity argon atmosphere. The as-cast ingots were pressed to
sized in (R,Pr)Fe
rare earth sublattice [4–7]. Therefore, much attention has been
paid to increase the concentration of Pr in (R,Pr)Fe cubic Laves
alloys. For example, Ren et al. recently reported the structure,
magnetic and magnetostrictive properties in Tb0:1Ho0:9ꢀxPr
0:1 compounds. They found that the introduction of a small
2
alloys when Pr is over a certain concentration in
6
3
GPa by a hexahedral anvil press and heated to 900 1C for
0 min. Conventional X-ray diffraction (XRD) analysis was carried
out using Cu Ka radiation with a Rigaku D/Max-gA diffractometer.
The lattice parameters were calculated using the Jade 5.0 XRD
analytical software (Materials Data, Inc., Livemore, CA). The
magnetization measurements were carried out using a vibration
sample magnetometer (7300, Lakeshore) under a magnetic field
up to 10 kOe. The shape of sample for magnetostriction measure-
ment was mainly disk-like with a diameter of 10 mm and a height
2
x
Fe0:9
B
amount of boron is beneficial to stabilize high-Pr content cubic
n
Corresponding author.
E-mail addresses: shiyangguang@gmail.com, shiyg@nuaa.edu.cn (Y.G. Shi).
0304-8853/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2011.12.023

1
628
Y.G. Shi et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1627–1630
x
Fig. 2. XRD patterns of Ho1ꢀxPr Fe1:9 alloys prepared by annealing under 6 GPa at
900 1C for 30 min.
Fig. 1. XRD patterns of Ho1ꢀxPr
00 1C for 30 min.
x
Fe1:9 alloys prepared by vacuum annealing at
9
of 2 mm. The linear magnetostriction was measured using stan-
dard strain-gauge technique in directions parallel ð Þ and per-
pendicular ð Þ to applied magnetic fields at room temperature.
l
J
l
?
3
. Results and discussion
In order to study the structure of Ho1ꢀxPr
x
Fe1:9 alloys prepared
by traditional high-temperature annealing method, the as-cast
samples were vacuum annealed at 900 1C for 30 min. The XRD
patterns for the samples with x ¼ 0:0, 0.2 and 0.4 are shown in
Fig. 1. It can be observed that the single cubic Laves phase with
MgCu
multiphase structure appears when the Pr concentration further
increases. For the sample with x ¼ 0:4, (Ho,Pr)Fe with PuNi -type
structure becomes the main phase and (Ho,Pr)Fe with MgCu
2
-type structure can only be stabilized with xr0:2. A
3
3
2
2
-
type is the secondary phase, coexisting with a small amount rare
earth phases. This is consistent with the structure of Tb0:1Ho0:9ꢀx
Pr
x
Fe0:9
B0:1 alloys, in which the single cubic Laves phase cannot be
x
Fig. 3. The lattice parameter a of Ho1ꢀxPr Fe1:9 Laves phase synthesized by
annealing under 6 GPa at 900 1C for 30 min.
stabilized when the Pr concentration is higher than 40 at% in rare-
earth sublattice even with the help of Tb and B [6,7].
In contrast with Fig. 1, the samples prepared by annealing
under high stress (Fig. 2) exhibit almost single cubic Laves phase
x
Laves phase with high-Pr content in Ho1ꢀxPr Fe1:9 should be
attributed to the effects of high stress.
with MgCu
rare earth phases. Generally, the atomic size plays an important
role in the formation of RFe cubic Laves alloys. It was estimated
2
-type structure, coexisting with minor impurities, i.e.
x
The lattice parameter (a) of Ho1ꢀxPr Fe1:9 Laves phase synthe-
sized under high stress is shown in Fig. 3. An approximate linear
2
increase with Pr-concentration from 0.0 to 1.0 is found, as
that the ideal radius ratio between R and Fe for a cubic Laves
phase is 1.225 [9]. As a result, it is difficult to obtain high-Pr
content cubic Laves phases under normal pressure due to the
large radius ratio between Pr and Fe. By the method of annealing
at ambient pressure, the element of Ho with its smaller radius can
expected from Vegard’s law: a ¼ xa
1
þð1ꢀxÞa
2 1 2
, where a and a
are the lattice parameters of PrFe1.9 and HoFe1.9, respectively. The
increase of lattice parameter with increasing Pr concentration is
3
þ
3þ
due to the larger ionic radius Pr
Magnetic field dependence of magnetization at 300 K for the
Fe1:9 is shown in Fig. 4(a). We can note that each sample
than that of Ho
.
stabilize Ho1ꢀxPr
x
Fe1:9 cubic Laves phase with Pr up to 20 at% in
Ho1ꢀxPr
x
rare-earth sublattice, but cannot hold when the Pr concentration
goes much higher. Therefore, the obtained stabilization of cubic
shows a tendency to saturation at the field of 10 kOe. For clarity,
the magnetization at the maximum available 10 kOe, denoted as

Y.G. Shi et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1627–1630
1629
decrease and following increase in the total net magnetization.
This behavior could also be found in Tb1ꢀxPr Fe1:9 and
Tb1ꢀxNd Fe1:9 alloy systems [10,11]. From the analysis the mag-
x
x
netization of the present alloy system, we can also get a conclu-
sion that the magnetic moment compensation point between Ho
and Pr should be in the range of 0:4rxr0:6 at room
temperature.
The linear magnetostriction of all the samples was measured
J
using standard strain-gauge technique in directions parallel ðl Þ
Fig. 4. (a) Magnetization curves of Ho1ꢀxPr
x
Fe1:9 cubic Laves alloys at 300 K and
Fe1:9 cubic Laves alloys at 300 K.
(
b) the magnetization 10k at 10 kOe of Ho1ꢀxPr
s
x
s10k, as a function of Pr concentration is plotted in Fig. 4(b). It can
be seen that s10k decreases with increasing Pr concentration to a
minimum at x ¼ 0:4, which is consistent with the variation of
x
saturation magnetization for Tb0:1Ho0:9ꢀxPr Fe0:9B0:1 alloys [6,7].
With further increasing x from 0.4 to 1.0, s10k increases mono-
tonously. This can be understood by the compensation of sub-
lattice magnetization: the moment of heavy rare earth Ho is
unparallel that of Fe, whereas the moment of light rare earth Pr is
Fig. 5. (a) The magnetostrictions
l
ꢀ
J
and
l
?
of Ho0:2Pr0:8Fe1:9 versus the applied
Fe1:9 cubic Laves alloys versus
as function of Pr
x
parallel to. The magnetic moment of Ho1ꢀxPr Fe1:9 can be
field, (b) the magnetostriction ð
l
J
l
?
Þ of Ho1ꢀxPr
x
described as: ms ¼ ð1ꢀxÞmHoꢀ1:9mFeꢀxmPr. As a result, the compe-
the applied field and (c) the magnetostriction
ðl
J
ꢀ
l
?
Þ
a
tition between these two sublattice moments leads to first
concentration.

1
630
Y.G. Shi et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 1627–1630
and perpendicular ð
temperature. As a typical representative, the magnetostrictions
and of Ho0.2Pr0.8Fe1.9 versus the applied field are presented
in Fig. 5(a). Fig. 5(b) shows the magnetostriction ð Þ of
l
?
Þ to applied magnetic fields at room
4. Conclusion
l
J
l
?
x
High-Pr content Ho1ꢀxPr Fe1:9 cubic Laves alloys which cannot
l
J
ꢀl
?
be synthesized at ambient pressure were successfully fabricated
by annealing under high stress. The structure, magnetic proper-
ties, and the magnetostriction of the alloys have been investi-
gated. The variation of saturation magnetization for Ho1ꢀxPr
is ascribed to the antiparallel moments between Ho and Pr.
PrFe1.9 possesses a much larger magnetostriction than HoFe1.9
Ho1ꢀxPr Fe1:9 ð0rxr1Þ versus the applied field. It is obvious
x
that HoFe1.9 possesses a much lower magnetostriction than
PrFe1.9. Besides, we can see that the magnetostriction of the
sample with high-Ho content ðxr0:4Þ is much harder to get
saturation than that of high-Pr content. This indicates that HoFe1.9
x
Fe1:9
.
should have a larger anisotropy than PrFe1.9
.
The magnetostriction does not linearly increase with increasing x,
but presents a minimum at x ¼ 0:4, which could be understood on
the basis of single-ion model.
In order to investigate the variation of magnetostriction with
J ?
different Pr concentrations, the magnetostriction ðl ꢀl Þ as a
function of x is plotted in Fig. 5(c). The magnetostriction increases
with the addition of Pr and shows a peak around x ¼ 0:2. This
tendency is very similar to that of Tb0:1Ho0:9ꢀxPr
x
Fe0:9
B
0:1 alloy
Acknowledgments
system, in which the sample with x ¼ 0:2 [6] or x ¼ 0:25 [7]
exhibits the largest magnetostriction. This is due to the
sample with x ¼ 0:2 or x ¼ 0:25 is very close to the anisotropy
This work was supported by Natural Science Foundation of
China (Grant nos. 51001061 and 50831006) and Natural Science
Foundation of Jiangsu (Grant no. BK2010499).
3
þ
3þ
and Pr . Consequently, the
compensation point between Ho
peak around x ¼ 0:2 in the present studied alloys could be
understood. With further increasing x to 0.4, the magnetostric-
tion exhibits a minimum value in the whole range of magnetic
fields, which is quite different from the magnetostriction
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0
.4 to 1.0, the magnetostriction of the system increases mono-
tonically, which could be ascribed to the larger magnetostriction
of PrFe1.9 than that of HoFe1.9
[
(
.