Crystal structure and magnetic properties of the compound MnN

Article abstract of DOI:10.1016/S0925-8388(00)00794-5

The compound MnN was prepared as a single phase by DC reactive sputtering. Its crystal structure is determined to be face-centered tetragonal one with the NaCl type by X-ray diffraction measurements. The compound MnN is stable up to 753 K and decomposes to tetragonal Mn₃N₂ at 758 K. This compound exhibits a antiferromagnetism.

Full text of DOI:10.1016/S0925-8388(00)00794-5

Journal of Alloys and Compounds 306 (2000) 66–71
L
www.elsevier.com/locate/jallcom
Crystal structure and magnetic properties of the compound MnN
a ,
b
b
b
b
c
*
K. Suzuki , T. Kaneko , H. Yoshida , Y. Obi , H. Fujimori , H. Morita
a
Tsuruoka National College of Technology, Tsuruoka 997-8511 Japan
Institute for Materials Research, Tohoku, University, Sendai 980-8577, Japan
Faculty of Engineering, Yamagata University, Yonezawa 992-8510, Japan
b
c
Accepted 23 February 2000
Abstract
The compound MnN was prepared as a single phase by DC reactive sputtering. Its crystal structure is determined to be face-centered
tetragonal one with the NaCl type by X-ray diffraction measurements. The compound MnN is stable up to 753 K and decomposes to
tetragonal Mn N at 758 K. This compound exhibits a antiferromagnetism.
 2000 Published by Elsevier Science S.A. All rights
3
2
reserved.
Keywords: MnN; Crystal structure; Magnetic properties
˚
1
. Introduction
thickness of about 500 A by nitriding vacuum-evaporated
Mn films with NH gas at 3008C [9]. The nitride film has a
3
˚
It is known that there are four stable intermediate phases
´, z, h, u) in the Mn–N system. The ´ phase has a
f.c.t. structure with the lattice constants a54.214 A, c5
˚
(
4.144 A. The specimen composition is Mn N5.32. They
8
face-centered cubic structure (f.c.c.), the z phase a hexa-
gonal closed packed one (h.c.p.). The h and u phases have
reported that its crystal structure is of the NaCl type with a
random distribution of N atoms among the octahedral
interstices. Moreover, they found that its tetragonal struc-
ture turned to a cubic one at 683620 K. They suggested
that the phase transition may be related to the magnetic
transition, because other compounds in the Mn–N system
such as Mn N [5] and Mn N [10] are known to be
face-centered tetragonal structures (f.c.t.). Mn N [1–3]
4
belongs to the ´ phase. Mn N [1,4], Mn N [2,5] and
5
2
2
Mn N
[6] belong to the z phase.
2
0.86
Mn N [1,4,7] belongs to the h phase. It is considered
3
2
that MnN belongs to the u phase [1]. These compounds are
2
4
prepared by reacting N or NH with Mn powder at high
magnetic materials.
2
3
temperatures in most cases.
The NaCl and ZnS structures are considered so far as
possible crystal structures for the AB type compound of 3d
transition metal nitrides. The AB type nitrides of scan-
dium, titanium, vanadium and chromium have the NaCl
type f.c.c. structure at room temperature [11–13,16]. We
have recently reported that the FeN, CoN and CrN
compounds can be prepared as a single phase by DC
reactive sputtering [14–16]. The FeN and CoN compounds
have not the NaCl type structure but the ZnS type f.c.c.
structure [14,15]. We have also investigated the magnetic
properties of FeN [14] and CoN [15].
Nishiyama et al. prepared Mn nitrides by nitriding Mn
powder with ammonium [8]. Among the prepared samples,
they found the MnN compound which has f.c.c. structure
with lattice constant a54.435 A (651 at.%N).
Lihl et al. prepared a series of Mn–N compounds with
˚
2
0.9–47.9 at.% N by reacting N2 or NH3 with Mn
amalgams [1]. The most N-rich phase (with 45.7–47.9
at.% N) has a f.c.t. crystal structure with the lattice
˚
˚
constants a54.221 A, c54.113 or 4.115 A (45.8 at.% N)
˚
˚
and a54.214 A, c54.148 A (47.9 at.%N).
Otsuka et al. prepared polycrystalline Mn-N films with a
The physical properties of the u phase in the Mn–N
system have been little studied, probably because of the
difficulty of specimen preparation. In this paper, it is
reported that the manganese nitride MnN was prepared by
the same method described in Refs. [14,15] and [16]. Then
the crystal structure and the thermal stability of the
*
Corresponding author. Tel.: 181-235-25-9148; fax: 181-235-24-
840.
E-mail address: suzuki@tsuruoka-nct.ac.jp (K. Suzuki)
1
0
925-8388/00/$ – see front matter
 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0925-8388(00)00794-5

K. Suzuki et al. / Journal of Alloys and Compounds 306 (2000) 66–71
67
prepared MnN compound were examined. The magnetic
properties were also investigated.
diffraction. The mixing ratios of the sample powder to
quartz powder are from 1 to 0.6.
In order to examine the thermal stability of the Mn–N
compound, powder samples were annealed at successively
higher temperatures for 2 h. After each annealing, the
crystal structure was examined at room temperature. The
magnetic properties of the powder sample were measured
with a VSM magnetometer
2
. Experimental procedure
The Mn–N sample was prepared by a high rate-type
triode DC reactive sputtering [14–16] in a mixture gas of
Ar1N . The sputtering conditions were as follows: target
2
voltage, 0.22 kV; target current, 50 mA; total gas pressure,
3. Results and discussion
2
2
22
3
.0310 Torr; N partial gas pressure, 0.80310 Torr;
2
27
residual gas pressure, 2.0310 Torr; and target–substrate
distance, 23 mm. A manganese disk of 99.9 percent purity
was used as a target, and a water-cooled Cu plate was used
as a substrate. The thickness of the deposited Mn–N film
was about 130 mm and it was stripped off from the
substrate mechanically. This stripped film was powdered.
Finally, the powder sample was stress relieved by anneal-
ing in vacuum at 510 K for 4 h.
3.1. Chemical and X-ray diffraction analyses
According to the result of gas chromatography, the
nitrogen content was 46.6 at.% N, and according to that of
ICP emission spectroscopy, the manganese content 48.7
at.% Mn. From the result of gas chromatography, the
residue was found to be oxygen. Consequently the N
content of the prepared Mn–N compound is estimated to
be more than 48 at.% N. Therefore, the atomic ratio of
manganese to nitrogen is almost 1:1.
The nitrogen content in the prepared sample was ana-
lyzed by gas chromatography, and the manganese content
was analyzed by ICP emission spectroscopy. The crystal
structure was examined by powder X-ray diffraction using
CuKa radiation. In order to prevent preferred orientation
of the sample, a mixture of powdered Mn–N compound
and quartz powder was used as the sample for the X-ray
Fig. 1 shows the X-ray diffraction pattern for the stress
relieved powdered Mn–N compound. All the diffraction
lines were well indexed as the f.c.t. structure. The lattice
˚
constants of the f.c.t. structure are a54.256 A and c5
˚
4.189 A with c/a 0.9843. The values of lattice constants
Fig. 1. Diffraction pattern for the powdered MnN compound.

6
8
K. Suzuki et al. / Journal of Alloys and Compounds 306 (2000) 66–71
are a little larger than those obtained by Lihl et al. [1] and
Otsuka et al. [9]. The value of c/a is almost the same as
obtained by Lihl et al. and Otsuka et al.
In the case of the f.c.t. structure as well as the f.c.c. one,
it is considered that the AB compound has either the NaCl
type structure or the ZnS type one. The atom positions in
the NaCl type structure and the ZnS type one are written
respectively in summary form as:
For the NaCl type structure
2
2
uFu 5 16( f 1 fN) when (h 1 k 1 l) is even
Mn
2
2
uFu 5 16( f 2 fN) when (h 1 k 1 i) is odd
Mn
For the ZnS type structure
2
2
2
uFu 5 16( f 1 f ) when (h 1 k 1 l) is odd
Mn
N
2
2
uFu 5 16( f 2 fN) when (h 1 k 1 l) is an odd multiple
Mn
4
4
Mn at (0 0 0) 1 face centering translations.
N at (1/2, 1/2, 1/2) 1 face centering translations.
of 2
2
2
uFu 5 16( f 1 fN) when (h 1 k 1 l) is an even multiple
Mn
and
of 2
.
where (h k l) are the indices of the diffraction lines, and
4
4
Mn at (0 0 0) 1 face centering translations.
N at (1/4, 1/4, 1/4) 1 face centering translations.
fMn and f are the atomic scattering factors of the Mn and
N atoms, respectively.
N
The difference in the atom positions between the two
structures is reflected on the structure factors, and causes a
large difference in the ratio of the diffraction line inten-
sities.
In Fig. 2, the experimental diffraction line intensities
were compared with the values calculated for the MnN
f.c.t. structure of the NaCl type and the ZnS type. The
calculated and experimental intensities are normalized to
the (111) line intensity. Here, the Debye temperature of
The above formulas indicate that the difference in
intensities between two structures becomes distinct when
the values of (h1k1l) are 2 and 6. As can be seen in the
figure, the calculated values for the NaCl type structure
agree well with the experimental values. However, those of
the ZnS type structure are substantially smaller than the
experimental values, especially at the (200) (002), (222)
and (420) (402) (204) lines. The values of the reliability
factor for the NaCl type structure and the ZnS type one are
11.2% and 42.3% respectively. From these results, the
crystal structure of the MnN compound is considered to be
the f.c.t. structure with the NaCl type (Fig. 3). This result
5
30 K is used in the temperature factor for the calculations.
In the calculations of the structure factors, we used atomic
scattering factors of neutral atoms [17].
Fig. 2. Relative X-ray diffraction intensities normalized to the (111) line.

K. Suzuki et al. / Journal of Alloys and Compounds 306 (2000) 66–71
69
z-phase appears at 848 K. The h-phase and z-phase
coexist between 848 K and 893 K.
4
5
6
. The h-phase decomposes wholly to the z-phase at 898
K. Only the z-phase exists as a single phase between
8
98 K and 978 K.
. A part of the z-phase begins to decompose and Mn N
4
appears at 983 K. The Mn N compound and the z-
4
phase coexist between 983 K and 1063 K.
. Only Mn N exists above 1068 K.
4
The results are summarized in Table 1
In Fig. 4 the lattice constants of the MnN and h-Mn N
3
2
compound are plotted against the annealing temperatures
Tan) in the range from 643 K to 843 K. Here, the lattice
constants a are derived from the (200) lines, c from the
002) lines in the X-ray diffraction patterns. In the figure,
(
(
the lattice constant a and c of MnN are shown with the
open and closed circles and a9 and (1/3)c9 of Mn N with
3
2
the open and closed triangles.
As seen in the figure, the a and c of the MnN compound
decrease gradually between about 670 K and 750 K. This
is attributed to a statistical absence of N atoms from the
compound. As shown in the figure, the MnN compound
decomposed abruptly to the h-Mn N compound between
Fig. 3. Crystal structure of the MnN compound.
3
2
7
53 K and 758 K. In the process of decomposing, the
is consistent with that reported by Otsuka et al. The MnN
compound prepared in this experiment belongs to the u
phase.
values of the lattice constant c decrease remarkably in
comparison with those of a. This indicates that a rapid loss
of N atoms in the c-plane occurs around 755 K.
In order to examine the real ratio of nitrogen to
manganese, chemical analysis was carried out for the
samples annealed at 738 K and 800 K. According to the
results of the analysis for the sample annealed at 738 K,
the nitrogen content was 39.7 at.% N, the manganese
content 52.7 at.% Mn. The residue was found to be
3
.2. Thermal stability
In order to investigate the thermal stability and the
decomposition process of MnN, X-ray diffraction measure-
ments were carried out at room temperature for the
samples annealed in vacuum for 2 h at successively higher
temperatures between 673 K and 1183 K. The results show
that
Table 1
Results of the X-ray diffraction measurements for the MnN compound
annealed in vacuum for 2 h at various temperatures
Annealing temperature
Phase analysis
1
2
. The MnN phase is stable up to 753 K.
(
K)
. At 758 K an extra line appears in addition to those for
the f.c.t. MnN compound. This line is well indexed as a
super lattice line on the basis of the crystal structure of
h-Mn N with ordered vacancies on the N sites of
6
7
73
13
u (MnN)
u (MnN)
u (MnN)
u (MnN)
h (Mn N )
738
753
3
2
7
8
8
8
58
00
43
48
MnN. The unit cell of the h-Mn N compound is
3
2
3
2
h (Mn N )
3
2
formed by removing N atoms from three unit cells of
the f.c.t. MnN compound stacked along the direction of
the c-axis. The c-planes of the f.c.t. MnN compound
have no N atoms every three layers. The lattice
constants of a sample annealed at about 800 K are
h (Mn N )
3
2
h (Mn N )1z
3
2
893
898
h (Mn N )1z
3 2
z
z
z
9
9
9
33
78
83
˚
˚
obtained to be a954.205 A, c9512.126 A at room
temperature. These values are in good agreement with
the values obtained for h-Mn N by Kreiner et a1. [7].
z1´ (Mn N)
4
1
033
´ (Mn N)1z
4
3
2
1063
1068
´ (Mn N)1z
4
Only the h-phase exists as a single phase between 758
K and 843 K.
. A part of the h-phase begins to decompose and the
´ (Mn N)
4
1
1
133
183
´ (Mn N)
4
´ (Mn N)
4
3

7
0
K. Suzuki et al. / Journal of Alloys and Compounds 306 (2000) 66–71
Fig. 4. The lattice constants of the MnN and h-Mn N compound plotted against the annealing temperatures (Tan). where s is a, d is c of the MnN and
3
2
n is a9, m is (1/3)c9 of the h-Mn N .
3
2
oxygen. The nitrogen content of MnN at 738 K is
estimated to be 37.7 at.% N. The same analysis was
performed for the sample annealed at 800 K. The nitrogen
content was 34.0 at.% N and the manganese content 57.1
at.% Mn. The residue was found to be oxygen. The
nitrogen content of h-Mn N at 800 K is estimated to be
4. Conclusion
The compound MnN was prepared as a single phase by
the DC reactive sputtering method. From the powder X-ray
diffraction experiments its crystal structure is determined
to be of the face-centered tetragonal one of the NaCl type.
3
2
2
9.8 at.% N. It is known that the h-phase has some
nitrogen concentration range (38.2|41.0 at.% N) [1]. The
present result shows that the h-phase has a broader range
than that found by Lihl et al. [1].
3
.3. Magnetic properties
Fig. 5 shows the temperature dependence of magneti-
zation at 10 kOe in the temperature range from 300 K to
00 K. The magnetization increases gradually with in-
creasing temperature in the range from 300 K up to about
40 K and has a broad maximum around 650 K. With
8
6
further increase of temperature the magnetization de-
creases, but its temperature dependence does not follow the
Curie–Weiss law.
Fig. 6 shows the magnetization curves at room tempera-
ture. The magnetization increases linearly with the field.
2
5
The susceptibility x is obtained to be 2.15310
g
2
1
emu g
.
The result suggests that the compound MnN is anti-
ferromagnetic with a N e´ el temperature around 650 K and
the tetragonal distortion is ascribed to an exchange stric-
tion by onset of magnetic order. In order to make clear the
magnetic properties and the origin of the tetragonal lattice
distortion, neutron diffraction and measurements of the
temperature variation of lattice constants and heat capacity
are now in progress.
Fig. 5. Temperature dependences of the magnetization for the MnN
compound at 10 kOe.

K. Suzuki et al. / Journal of Alloys and Compounds 306 (2000) 66–71
71
Acknowledgements
This work was performed under the inter-university
cooperative research program of the Institute for Materials,
Tohoku University.
References
[
[
[
[
[
[
[
[
1] F. Lihl, P. Ettmayer, A. Kutzelnigg, Z. Metallk. 53 (1962) 715.
2] G. H a¨ gg, Z. physik. Chem. B4 (1929) 346.
3] U. Zwicker, Z. Metallk. 42 (1951) 274.
4] O. Prelinger, Monatsh. Chem. 15 (1894) 391.
5] M. Mekata, J. Haruna, H. Takei, J. Phys. Soc. Jpn. 25 (1968) 234.
6] M. Eddine, Acta Cryst. B33 (1911) 2696.
7] G. Kreiner, H. Jacobs, J. Alloys Comp. 183 (1992) 345.
8] Z. Nishiyama, R. Iwanaga, Nippon Kinzoku Gakkai-Shi 9 (9)
(
1945) 1.
9] N. Otsuka, Y. Hanawa, S. Nagakura, Phys. Stat. Sol. (a) 43 (1977)
27.
[
1
[10] W.J. Takei, G. Shirane, B.C. Frazer, Phys. Rev. 119 (1960) 112.
[11] K. Kume, H. Yamagishi, J. Phys. Soc. Jpn. 19 (1964) 414.
[12] W. Wong-Ng, H.F. McMurdie, B. Paretzkin, Y. Zhang, K.L. Davis,
C.R. Hubbard, A.L. Dragoo, J.M. Stewart, Powder Diffr. 2 (1987)
2
00.
[
[
13] R. Blix, Z. physik. Chem. B3 (1929) 229.
14] K. Suzuki, H. Morita, T. Kaneko, H. Yoshida, H. Fujimori, J. Alloys
Comp. 201 (1993) 11.
[
15] K. Suzuki, T. Kaneko, H. Yoshida, H. Morita, H. Fujimori, J. Alloys
Comp. 224 (1995) 232.
Fig. 6. Magnetization curves for the MnN compound at room tempera-
ture. d: increasing magnetic field. s: decreasing magnetic field.
[16] K. Suzuki, T. Kaneko, H. Yoshida, Y. Obi, H. Fujimori, J. Alloys
Comp. 280 (1998) 294.
˚
[17] J.A. Ibers, W.C. Hamilton, in: International tables for X-ray crys-
tallography, Vol. IV, Kynoch Press, Birmingham, UK, 1974, p. 73,
also page 77.
The lattice constants are obtained to be a54.256 A and
˚
c54.189 A. The MnN compound is stable up to 753 K,
and decomposes into the Mn N compound with tetragon-
3
2
al structure at 758 K. From the magnetic measurements the
compound MnN was found to be antiferromagnetic.