Neutron diffraction studies of the compounds MnN and FeN

Article abstract of DOI:10.1143/JPSJ.70.1084

The compounds MnN and FeN were prepared as single phase sample by DC reactive sputtering. The crystal structure of MnN is tetragonally distorted NaCl type and that of FeN is ZnS type. Temperature dependence of the neutron diffraction pattern on MnN was in

Full text of DOI:10.1143/JPSJ.70.1084

Journal of the Physical Society of Japan
Vol. 70, No. 4, April, 2001, pp. 1084–1089
Neutron Diffraction Studies of the Compounds MnN and FeN
Kenji Suzuki*, Yasuo Yamaguchi1, Takejiro Kaneko1, Hajime Yoshida1,
Yoshihisa Obi1, Hiroyasu Fujimori1 and Hiroaki Morita2
Tsuruoka National College of Technology, Inooka Sawada 104, Tsuruoka 997-8511
1Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577
2Faculty of Engineering, Yamagata University, Jonan 4-3-16, Yonezawa 992-8510
(Received September 5, 2000)
The compounds MnN and FeN were prepared as single phase sample by DC reactive sputter-
ing. The crystal structure of MnN is tetragonally distorted NaCl type and that of FeN is ZnS
type. Temperature dependence of the neutron diffraction pattern on MnN was investigated.
Analysis of the data shows that the magnetic structure of MnN consists of ferromagnetically
aligned c-planes coupled antiferromagnetically in the c-direction. The magnetic moment of
manganese atom extrapolated to 0 K was found to be 3.3μB and lie in c-plane. The neutron
diffraction measurements of the compound FeN were also carried out. The ZnS type FeN was
concluded to be non-magnetic down to 2.2 K.
KEYWORDS: MnN, FeN, crystal structure, neutron diffraction, magnetic structure
§1. Introduction
by chemical reaction. Hinomura and Nasu prepared two
kinds of Fe nitrides whose chemical compositions were re-
ported to be FeN0.63 and FeN0.65
17) which have the crys-
tal structure of NaCl type (a = 4.50 A) and that of ZnS
It is known that there are four stable intermediate
phases (ε, ζ, η, θ) in Mn–N binary alloy system. The
ε phase has a face-centered cubic structure (f.c.c.), the
ζ phase a hexagonal closed packed one (h.c.p.) and
the η and θ phases face-centered tetragonal structures
(f.c.t.). Mn4N belongs to the ε phase.1–3) Mn5N2, Mn2N
and Mn2N0.86 belong to the ζ phase.1, 2, 4–6) Mn3N2 be-
longs to the η phase.1, 4, 7) About the magnetic proper-
ties of Mn–N system, Mn4N exhibits ferrimagnetism,8)
,
˚
˚
one (a = 4.33 A), respectively. They also reported about
FeN0.91 of nearly single phase of the ZnS type compound.
They carried out the measurements of M¨ossbauer effect
on these compounds, and found that ZnS type Fe nitride
is a non-magnetic substance in which Fe atoms have no
local magnetic moments. And they reported that the
NaCl type Fe nitride exhibits an antiferromagnetism.
We also reported the preparation of FeN samples as
single phase compound by DC reactive sputtering.18)
The atomic ratio of iron to nitrogen in the sample was
almost 1 : 1, and the crystal structure was determined to
be ZnS type by X-ray diffraction measurements. We ob-
served a small asymmetric magnetic hysteresis loop after
field cooling. It looks like an evidence of micto-magnetic
state of FeN.18)
7)
and Mn5N2,9) Mn2N10) and Mn3N2 exhibits anti-
ferromagnetism. Recently, the neutron diffraction mea-
surement for Mn6N5.26 was carried out by Leineweber
and Niewa et al.11) The compound MnN was prepared
by reacting N2 or NH3 with Mn amalgams,1) or prepared
by nitriding vacuum-evaporated Mn films with NH3 gas
at 300◦C.12) MnN belongs to the θ phase. There is no
report on magnetic property of MnN.
In the previous paper we reported the production
process of the single phase compound of MnN of al-
most stoichiometry.13) The crystal structure determined
by X-ray diffraction measurements was tetragonally dis-
torted NaCl type. The lattice constants of the struc-
In the present investigation, we have prepared stoichio-
metric MnN and FeN compounds by DC reactive sput-
tering, and studied the crystal and magnetic structures
using neutron diffraction technique in order to clarify
origin of their magnetic property.
˚
˚
ture are a = 4.256 A and c = 4.189 A at room temper-
ature. According to the results of magnetic measure-
ments, the magnetic susceptibility of MnN shows a max-
imum around 650 K, and we concluded that MnN is an-
tiferromagnetic with the N´eel temperature of 650 K.
In the Fe–N system there are several types of stable
§2. Experimental Procedure
The MnN sample was prepared by high rate-type
triode DC reactive sputtering apparatus in Ar + N2
mixed gas.13) The sputtering conditions were as fol-
compounds. Among them, there are many reports on γꢀ- lows: target voltage, 0.22 kV; target current, 50 mA; to-
tal gas pressure, 3.0×10−2 Torr; N2 partial gas pressure,
Fe4N, which exhibits ferromagnetism.14, 15) In the quasi-
0.80 × 10−2 Torr; and target-substrate distance, 23 mm.
stable compound αꢀꢀ-Fe16N2 it is well known that Fe
atom has larger magnetic moment than in pure iron.16)
A manganese disk of 99.9% purity was used as a target,
On the other hand, there have been only a few reports and water-cooled Cu plate was used as a substrate. The
thickness of the deposited Mn–N film was about 120–
on FeN because of the difficulty of sample preparation
175 μm and it was mechanically stripped off from the
∗E-mail: suzuki@tsuruoka-nct.ac.jp
1084

2001)
Neutron Diffraction Studies of the Compounds MnN and FeN
1085
Fig. 1. X-ray diffraction pattern of the powdered MnN compound at room temperature.
substrate. This stripped film was powdered, and then §3. Results and Discussion
annealed at 510 K for 4 hours in vacuum in order to re-
3.1 MnN
lieve stress. The FeN sample was also prepared in the
The neutron diffraction measurements were carried
out at 16 K, 295 K and 450 K, respectively. Figure 3
shows the neutron diffraction pattern at 16 K. Peaks
of the nuclear reflexions were indexed as (hkl) and peaks
of the magnetic reflexions as ∗(hkl) in the figure. All nu-
clear peaks were well indexed as an tetragonally distorted
NaCl-type structure in the neutron diffraction measure-
ment as well as in the X-ray diffraction one. Except for
the decreasing of magnetic reflexions compared with the
nuclear reflexions, the diffraction patterns at 295 K and
450 K were essentially same as the case at 16 K.
same way as described above from 99.9% Fe target.
Chemical analysis showed that the nitrogen concentra-
tion in these compounds was almost 50 atomic% within
the experimental error. Figures 1 and 2 show the X-
ray diffraction patterns using CuKα at room tempera-
ture for the annealed powder of the MnN and FeN com-
pounds, respectively. In the case of MnN, peak positions
are well indexed by face-centered-tetragonal lattice with
˚
˚
the lattice constants of a = 4.256 A and c = 4.189 A.
On the other hand, diffraction pattern is explained by
˚
face-centered cubic lattice with a = 4.307 A for FeN.
As shown in the figure, magnetic reflexions were in-
dexed as ∗(001), ∗(110), ∗(201)(021) and ∗(112). The
magnetic reflexion of ∗(100) is not observed, which in-
dicates that the magnetic moment of Mn atom cancel
out in a (100) plane. The magnetic reflexion of ∗(011)
is not observed, either. These results indicate that the
magnetic structure of MnN has an antiferromagnetic ar-
rangement as shown in Fig. 4, which is known as the
first kind antiferromagnetic ordering of f.c.c. lattice. The
magnetic moments of Mn atoms align ferromagnetically
in a c-plane and the ferromagnetic c-plane couples anti-
ferromagnetically with the adjacent c-plane each other.
The magnetic moments lie in the c-plane, and the direc-
tion in the c-plane cannot be determined by a powder
neutron diffraction measurement.19)
The weight of the samples used for neutron diffraction
experiment was about 1 g. A powder neutron diffraction
experiment was carried out using HERMES diffractome-
ter which is installed in the research reactor JRR-3M at
the Japan Atomic Energy Research Institute. The in-
cident neutron was monochromatized using a vent Ge
˚
crystal with neutron wave length of 1.8197 A. A He gas
closed cycle refrigerator was used for the experiment in
the temperature range between 2.2 K and 295 K. The
powder sample was put into a vanadium holder (10.0 mm
diameter) and was packed in a micro cylinder of alu-
minum with heat exchange He gas. An electric furnace
was used for measurements above room temperature.
The intensities of the nuclear reflexions and the mag-

1086
Kenji Suzuki et al.
(Vol. 70,
Fig. 2. X-ray diffraction pattern of the powdered FeN compound at room temperature.
3.3μB at 16 K, 3.2μB at 295 K and 2.1μB at 450 K, and
the magnetic form factor of Mn2+ is used.20) Here, the
temperature factor is taken into consideration for the
calculations. In the table, the calculated and observed
relative intensities are normalized to the value of (111)
line, and values of scattering amplitudes of Mn and N
are −0.373 and 0.936 in 10−12 cm unit, respectively.21)
As shown in the table, the calculated values are consis-
tent with the observed values with the reliability factor of
6.4% at 16 K, 7.8% at 295 K and 12.5% at 450 K. We also
took diffraction pattern at 550 K, but the sample decom-
posed in vacuum. So, we cannot say anything more, but
temperature dependence of the magnetic intensity shown
in Table I is not inconsistent to the fact of TN = 650 K.
In the magnetic structure shown in Fig. 4, a Mn-ion
have six neighboring Mn-ions coupled by 180◦ superex-
change interaction via N-ion. Four of them are on the
same c-plane, and two of them are in the c-direction. All
of these neighbors couple ferromagnetically with the cen-
tral Mn-ion. Also a Mn-ion have twelve neighboring Mn-
ions coupled by 90◦ superexchange interaction. Four are
on the same c-plane, and couple ferromagnetically with
the central Mn-ion. And eight are on the adjacent c-
planes, and couple antiferromagnetically with the central
Mn-ion. These results seems to indicate that 180◦ su-
perexchange interaction of Mn–N–Mn is ferromagnetic,
and 90◦ superexchange interaction is antiferromagnetic
in MnN. This is very interesting as the signs of the ex-
change interactions are perfectly reversed compared with
Table I. Calculated and observed neutron diffraction intensities
for the MnN compound at 16 K, 295 K and 450 K. The intensi-
ties are normalized to the (111) line. Asterisk in front of index
indicates magnetic reflexion.
16 K
Icalc.
295 K
450 K
hkl
Iobs.
Iobs.
Icalc.
Iobs.
Icalc.
∗001
∗110
0.25
0.11
1.00
0.09
0.05
0.04
0.09
0.93
0.05
0.01
0.96
0.25
0.10
1.00
0.11
0.05
0.04
0.12
1.05
0.06
0.03
1.17
0.23
0.09
1.00
0.08
0.04
0.04
0.09
0.89
0.04
0.01
0.84
0.23
0.10
1.00
0.11
0.05
0.04
0.12
0.99
0.06
0.03
1.06
0.10
0.04
1.00
0.10
0.01
0.02
0.08
0.74
0.03
0.02
0.51
0.10
0.04
1.00
0.11
0.02
0.02
0.11
0.96
0.06
0.03
0.98
111
200, 002
∗201, ∗021
∗112
220, 202
311, 113
222
400
331, 313
R factor
6.4%
7.8%
12.5%
Magnetic
moment for
Mn
3.3μB
3.2μB
2.1μB
netic reflexions based on the model shown in Fig. 4 are
calculated. The results are shown together with the ob-
served intensities at 16 K, 295 K and 450 K in Table I,
where the magnetic moment of Mn atom is taken as

2001)
Neutron Diffraction Studies of the Compounds MnN and FeN
1087
Fig. 3. Neutron diffraction pattern of the MnN compound at 16 K. Nuclear reflexions are denoted by (hkl) and magnetic reflexions by
∗(hkl).
Therefore, in the present paper, the exchange interaction
J1 between the 1st nearest neighboring Mn atoms and
J2 between the 2nd nearest neighboring Mn atoms are
estimated on the basis of the molecular field calculation
for the 1st kind antiferromagnetic ordering in the f.c.c.
structure by Smart using TN and S obtained experimen-
tally.22) If we use values of TN = 650 K and S = 3/2, J1
and J2 are obtained to be −29 K and 24 K, respectively.
3.2 FeN
For the compound FeN, the neutron diffraction mea-
surements were carried out at 2.2 K and 290 K. Figure 5
shows the neutron diffraction pattern at 2.2 K. As shown
in the figure, the nuclear reflexions (111), (220), (311),
(400) and (331) were well indexed as an f.c.c. struc-
ture. The nuclear reflexions (200), (222) and (420) were
not observed. The reason is as follows: When the val-
ues of h + k + l are an odd multiple of 2 in the ZnS-
type structure, the structure factor |F| = 4(bFe − bN)
per unit cell, where bFe and bN are scattering ampli-
Fig. 4. Antiferromagnetic structure of the MnN compound. Mag-
netic moments lie in c-plane.
tude of Fe and N atom, respectively. In this case the
value of bFe (= 0.960 × 10−12 cm) is very close to that
of bN (= 0.936 × 10−12 cm).21) Therefore, (200), (222)
and (420) peaks were not observed in this experiment
the Mn–O–Mn case in MnO.
because of their extremely weak intensities.
As shown in the previous report, χg does not follow the
Curie-Weiss law above TN .13) Thus paramagnetic Curie
temperature θP and Curie constant C can not be esti-
mated. It is considered to be due to coming out of ni-
trogen atoms from the compound at high temperatures.
The neutron diffraction pattern at 290 K is almost the
same as one at 2.2 K. The results of the intensity calcu-
lations are shown together with the observed intensities
at 2.2 K in Table II. The calculated and observed inten-
sities are normalized to the (220) line. As shown in the

1088
Kenji Suzuki et al.
(Vol. 70,
Fig. 5. Neutron diffraction pattern for the FeN compound at 2.2 K.
al.23) They calculated the total energy of non-magnetic
state of the ZnS type FeN compound, and they predict
FeN to be non-magnetic from simple estimation of ferro-
magnetic and antiferromagnetic condition.
Table II. Calculated and observed neutron diffraction intensities
for the FeN compound at 2.2 K. The intensities are normalized
to the (220) line.
hkl
Iobs.
Icalc.
111
200
220
311
222
400
331
420
0.83
0.00
1.00
0.77
0.00
0.33
0.76
0.00
0.77
0.00
1.00
0.82
0.00
0.37
0.87
0.00
§4. Conclusion
We made the compound MnN as a single phase sam-
ple by the DC reactive sputtering method, and studied
the crystal and magnetic structures by means of neu-
tron diffraction measurements at 16 K, 295 K and 450 K.
The crystal structure of MnN is tetragonally distorted
NaCl type. From the powder neutron diffraction exper-
iments, the magnetic structure of MnN was determined
to have the 1st kind antiferromagnetic structure of the
f.c.t. lattice. The magnetic moment of manganese atom
was found to be 3.3μB at 16 K, 3.2μB at 295 K and 2.1μB
at 450 K, respectively.
R factor: 3.64%.
table, the calculated values are in good agreement with
the observed values with the reliability factor of 3.64%.
There was observed a small asymmetric magnetic hys-
teresis loop after field cooling,18) but there is no sign
of magnetic ordering in the present neutron diffraction
result as shown in Fig. 5. Therefore, above-mentioned
small asymmetric hysteresis loop may be attributed to
small amount of impurity which cannot be detected by
X-ray and neutron diffraction measurements.
This is consistent with the result of M¨ossbauer effect of
the ZnS type FeN0.91 compound.17) The lattice constant
of FeN prepared by us is in good agreement with the
equilibrium lattice constant of the ZnS type FeN com-
pound in the band calculation by Shimizu and Shirai et
We also made single phase sample of FeN by the same
method, and studied by neutron diffraction. The crystal
structure is the ZnS type, and there is no magnetic order
in FeN down to 2.2 K.
Acknowledgement
This work was performed under the inter-university
cooperative research program of the Institute for Mate-
rials Research, Tohoku University. We are grateful to
Dr. H. Shimizu for providing us with the results of band
calculations and useful discussions.
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