Ferromagnetic-Alloy Phases Near the Compositions Ni 2 MnIn , Ni 2 MnGa , Co 2
MnGa , Pd 2 MnSb , and PdMnSb
F. A. Hames
Citation: Journal of Applied Physics 31, S370 (1960); doi: 10.1063/1.1984753
View online: http://dx.doi.org/10.1063/1.1984753
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JOUR~AL
OF
APPLIED
SUPPLEME:'<T
PHYSICS
TO
VOL.
31,
NO.5
MAY,
1960
Ferromagnetic-Alloy Phases Near the Compositions NizMnln
Ni 2 MnGa, Co 2 MnGa, Pd 2MnSb, and PdMnSb*
'
F. A. HA>!ES
Department oj Jletallurgical i,.'ilgineering, Queen's Unic'ersity, Kingston, Ontario
. In a .search for .further examples of Heusler-type alloys, ferromagnetic alloys were found near the composition N:,YlnIn, NlzMnGa, Co,MnGa, Pd 2MnSb, and PdYlnSb. The first four alloys are tentatively identified
as havmg the L2 1(Heusler)-type structure; PdMnSb, the Cl,-type structure. Previous work has indicated
that ferromagnetism in these types of alloys is associated with Mn-Mn distances in the range 4.17-4.37 A.
The present work indicates that ferromagnetism persists with Mn-Mn distances as small as 4.08 A
(C0 2MnGa) and as large as 4.42 A (PdMnSb); and that ferromagnetism disappears if the Mn-Mn distances
become too large. Pd 2MnSb, with Mn-Mn distance 4.55 A, is only feebly magnetic at room temperature.
INTRODUCTION
T
HE Heusler alloys form an interesting group for
magnetic study because they offer a possible
means of investigating the effects of interatomic distances, atomic arrangement and atomic environment of
the magnetic atoms on the occurrence of ferromagnetism on the one hand, and of deducing alloying valences
of the metals from measured magnetic moments on the
other hand.
The classical Heusler alloys are the ferromagnetic
copper-manganese-aluminum alloys based on the beta
phase (body-centered cubic structure) of the binary
copper-aluminum system. They have a rather wide
composition range, which includes. the composition
CU2MnAl. They have an ordered cubic structure under
suitable conditions of heat treatment. Maximum degree
of order is obtained at composition CU2MnAI and the
atomic arrangement in this alloy is usually assumed to
be that proposed by Bradley and Rogers. 1 The structure
may be described in terms of the atoms occupying four
types of atom sites, herein designated A, B, C, and D,
whose coordinates are
A
0 0 0
1
1
"2 "2 0
1
1
0
"2
"2
0 t "21
4
3
'4
3
'4
1
4"
!3
'4
1
'4
.1.
4
i3 i;!
4"
D
C
B
.1.
4
1
"2
1
"2
"2
1
;!
4
;!
1
.1.
;!
4
1
i
0 0 "2
0 "21 0
t 0 0
4
'4
3
'4
;I
.1.
4
;!
4
;!
;I
1
'4
1-
4'
In CU2MnAI, A and C are occupied by eu; B by Mn;
and D by Al atoms. This arrangement corresponds with
space group Oh"-Fm3m and is the prototype of the
"Strukturbericht" L21 structure.
Other examples of this structure are found in ferromagnetic manganese alloys having the ideal composition JVhMnX, where M is Cu, Ni, or Co, and X is a B
sub-group metal. Pearson2 lists the following examples
(lattice constant, a, in parentheses).
Cu 2MnAI (5.937); CU2MnGa (?); CU2MnIn (6.1865);
* The research for this paper was supported in part by the
Defence Research Board of Canada.
1 A. J. Bradley and J. W. Rodgers, Proc. Roy. Soc. (London)
A144, 340 (1934).
'
2 W. B. Pearson, A Handbook oj Lattice Spacings and Structures
of jilek/is and Alloys (Pergamon Press, New York, 1958).
CU2.:\InSn (6.1608); NhMnSb (6.001); Ni 2MnSn
(6.036); C02~InSn (5.977).
CI I s.t~uctures (space group Ti- F43m) of ideal
compOSItIOn :;vIMnX are obtained in some instances by
lea:ing half of the M atoms out of the Heusler alloy,
ThIS leaves one set of sites (the C sites, for example)
unoccupied. Nil'.fnSb (5.903) and ColHnSn (5.956) are
in this category.
Co::vJ:nSb (5.888) is described as having a Cll-fluorite
structure with Co ordered in the A sites, but Mn and
Sb occupying the Band D sites randomly.
It is not certain that all of the Heusler alloys listed
above have an atomic arrangement analogous to that
describe.d for CU22'.'lnAI, i.e., M in A -and C; lIn in B;
and X III D; space group Oh"-Fm3m. An alternative
arrangement is: M in
- A and B', Mn in C', and X in D',
space group T}- F43m. Determination of the correct
arrangement by x-ray diffraction alone is difficult if
differences between atomic scattering factors of the
atoms are not favorable. Castelliz3 has discussed this
problem and has suggested a method of distinguishing
between the two arrangements, making use of measured
magnetic moments.
It is of interest to inquire as to the roles of various
atoms in the Heusler alloy as regards contribution to
magnetic moment. The B sub-group metal appears to
be unimportant, except possibly for its size and valence.
These might be important in determining the structure
of the alloy and whether or not there is a superiattice,
according to the alloying concepts of Hume-Rothery.
It is generally assumed that the magnetic moment
is due entirely to manganese, although Slater4 has suggested that copper may also be contributing to the magnetization in the copper-manganese-aluminum Heusler
alloy. Mn-Mn distances appear to be significant. Coles,
Hume-Rothery, and Myers," comparing CU2MnAI with
Cu 2MnIn, note a decreasing Curie point with increasing
interatomic distance and suggest that in CU2MnIn the
critical ratio of interatomic distance to 3d electron shell
L. Castelliz, Z. Metallk. 46, 198 (1955).
(1930).
5 B. R. Coles, W. Hume-Rothery, and H. P. Myers, Proc. Roy,
Soc. (London) A196, 125 (1949).
3
4
J. Slater, Phys. Rev. 36, 57
370S
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Ki~Mnln,
:\izl\lnGa,
Cod,fuGa,
PdzlVlnSb,
AKD
PdMnSb
ALLOYS
371S
TABLE I. Structure of the alloys (tentative). Q and Fe indicate
quenching and cooling in the furnace, respectively, after 24 hrs at
the temperature indicated.
examples of Heusler alloys has been undertaken. Some
preliminary results are summarized in Table 1.
-==========================
RESULTS AND DISCUSSION
Ideal
composition
a,A
:vfn-Mn
distance,A
L21 (Heusler) Structures
6.07
~i2~ln][n
6.08
5.86
~hMnGa
5.83
5.77
C02MnGa
5.78
6.38
PdzMnSb
6.43
4.29
4.30
4.14
4.12
4.08
4.09
4.51
4.55
Ch Structure
PdMnSb
4.42
6.25
Treatment
Q8WC
FC
Q 940°C
FC
Q 940°C
FC
Q 590°C
FC
diameter is being approached at which ferromagnetism
will disappear.
When transition metals such as nickel and cobalt are
substituted for copper, the problem of the interpretation
of measured magnetic moments is complicated because
of the presence of two kinds of potentially magnetic
atoms. There is then the question of the relative importance of ~I-J\I, J\1-lIn, and l\fn-i\ln interactions in
determining ferromagnetism; and the associated question of the relative importance of M-M, ::V1-Mn, and
Mn-Mn distances.
The question of the correct atomic arrangement
(Oh 5 vs Ti) in the various Heusler alloys is perhaps not
significant if it is only the :\In-J\In distances that are
important; in both arrangements the shortest IVln-l\In
distance is [(2N2]a. On the other hand, if ::\1-::\ln or
i\I-M distances are significant, knowledge of the correct
arrangement is desirable. In 0,," }1-i\I=a/2; i\I-i\In
= [(3)t/4]a, In Ti, :\1-i\1= [(3)t/4]a, i\1-=\In=a/2.
This question has been discussed by Castelliz3 in the
same reference noted above.
As an aid to resolving questions of the relative importance of atomic arrangement, interatomic distances,
and the environment of the magnetic atoms on the
occurrence of ferromagnetism, a search for further
All of the alloys were magnetic in all conditions of
heat treatment examined, as indicated by attraction to
a magnet; attraction was strong, excepting Pd 2MnSb.
The structures indicated are tentative. The X-ray
patterns were not inconsistent with the structures indicated, but other structures would give similar patterns,
in view of the unfavorable differences in atomic scattering factors.
It is noted that the Mn-Mn distances in the strongly
magnetic alloys range from 4.08 A (C0 2MnGa) to 4.42 A
(Pdl\fnSb), the distances for previously reported alloys
of these types range from 4.17 A (NiMnSb) to 4.37 A
(Cu2MnIn). In Pd 2MnSb, which is weakly magnetic,
the corresponding distance is 4.55 A.
CONCLUSIONS
1. Ki 2i\InIn, Ni 2l\InGa, C0 2MnGa, and Pd2l\InSb
are tentatively identified as having the L2 1 (Heusler)
structure; PdMnSb the Ch structure.
2. Ferromagnetism is strong in the alloys with
i\In-Mn distances in the range 4.08 to 4.42 A.
3. Ferromagnetism is weak (at room temperature,
at least) in Pd 2MnSb, Mn-Mn 4.55 A.
4. Although it appears that ferromagnetism might be
associated with a critical range of Mn-Mn distances, it
is not possible at present to separate this effect from the
possible ferromagnetism of Ni or Co interactions.
ACKNOWLEDGMENTS
The writer wishes to acknowledge assistance received
from the International Nickel Company. The indium
was donated by the Consolidated Mining and Smelting
Company of Canada, Limited; and the nickel and cobalt
by Sherritt Gordon Mines Limited. Donald Lea and
Brian Stevens assisted with the experiments.
The permission of the Defence Research Board of
Canada to publish this paper is gratefully acknowledged.
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