EFFECT OF Mn ON THE MAGNETIC
A. S. SCHAAFSMA,
M. J. BESNUS*,
Solid State Physics Laboratory,
Miissbauer
compounds.
manganese
MOMENTS
Materials
OF Fe IN INTERMETALLIC
I. VINCZET
COMPOUNDS
and F. VAN DER WOUDE
Science Center, Unioersiiy of Groningen, Groningen, The NetherIan&
and magnetic measurements
are reported on the ferromagnetic
Assuming
proportionality
between the iron hyperfine
field
is nonmagnetic
in these systems.
Much research has been carried out in recent
years on the magnetic
properties
of intermetallic
compounds.
The magnetic moment associated with
the transition metal atoms is often extremely sensitive to the composition
in pseudobinary
compounds. Direct neutron determination
of the individual magnetic
moments
is difficult because of
large nuclear
scattering
and strong correlation
effects. The combination
of Mossbauer
experiments
with bulk
magnetization
measurements,
however, can be useful in the study of 3d magnetic
moments of pseudobinary
systems.
The aim of the present work is to investigate the
effect of Mn substitution
in the ferromagnetic
intermetallic compounds
Fe,Y and Fe,B. The crystal
structure and the local neighbourhood
of the transition metal atoms are quite different in these systems. The Fe,Y has a cubic Cl5 Laves phase
structure, and the Fe atoms are surrounded
by 6
Fe at 2.57 A. The Fe,B has a body-centered-tetragonal Cl6 structure
whereas an Fe atom has 4B
nearest neighbours
at 2.18 A and 11 metal near
neighbours
between 2.41 and 2.72 A. Both crystal
structures remain unchanged
for the Mn substitution. These compounds
are ferromagnetic,
the magnetic moment of iron is 1.91 ps in Fe,B [l] and 1.45
pLe in Fe,Y [2], the yttrium has no intrinsic magnetic moment. Both the Mn,B [l] and the Mn,Y [3]
are Pauli paramagnets.
The samples were prepared by induction melting
under argon atmosphere.
The phase homogeneity
was checked by X-ray powder diffraction.
The
magnetization
measurements
in the (Fe, _,Mn,),Y
series were made on powdered
samples by the
induction
method
in a superconducting
coil in
(Fe,_,Mn,)2Y
and (Fe, _xMn,)2B
intermetallic
and iron magnetic
moment
it is found that the
fields up to 60 kOe. Curie temperatures
were obtained from magnetization
measurements
in a low
field. In the case of (Fe,_,Mn,),B
the results of
Cadeville
[l] were used. The Mijssbauer
spectra
were recorded at 5 K with a conventional
constant
acceleration
spectrometer.
The results are shown in figs. 1 and 2. The Curie
temperature
of both systems decreases almost linearly with the Mn concentration
and the ferromag=
0.6
for
(Fe, _xMn,),B
[l]
netism disappears at x,
c
GZ
0.7
for
(Fe,_,Mn,),Y,
respectively.
In
and at x
the case of (Fe,_,Mn,),Y
our result agrees quite
well with the recent magnetic
measurement
of
Hilscher and Kirchmayr
[4]. The average magnetic
moment of transition
metals ,&, drops faster than
simple dilution in both systems, the initial slope is
d,G&/dx
= - 2.7 pn/Mn atom for (Fe,_,Mn,),B
and
d,&,/dx
= - 1.8 pa/Mn
atom
for
(Fe, _xMn,),Y.
The average iron hyperfine
field,
H,, decreases
alwaysless
rapidly than j&,
the
initial
slopes are dH,,/dx
= - 110 kOe/Mn
atom in (Fe,_,Mn,),B
and dgr,/dx
= - 60
4 TC [K]
1000 ‘L
.
(Fel_x
800 -
.
600 -
MnX12B
(Cadevllle
1965
1
.
.*.
400 -
7 .
l
2oo -iFe,-XMn~+?
.
.
lInstitut de Physique,
Universiti
Louis Pasteur,
France.
j-On leave from the Central
Research
Institute
Budapest.
Journal of Magnetism
and Magnetic Materials
Strasbourg,
for
Physics,
0
i,i,lTl)
0.2
0.4
06
08
X
Fig. 1. Concentration
dependence
of the Curie temperature
in
(Fe, -xMnx)2Y (V, this work) and (Fe, _xMn,),B
(0, ref. 1).
15- 18 (1980) 1149- 1150 BNorth Holland
1149
A. S. Schaafsma et al./ Zero Mn moment in the intermetallic compounh
GF,[kOel
250
6
*
.
systems we find that the initial decrease in the
average
iron magnetic
moments
is d&,/dx
=
- 0.8 pa/Mn
atom and d,i&/dx
= - 0.4 &Mn
atom, respectively.
Since djXrM/dx = PMn - pre
+ d&/dx,
we find that manganese
atoms have
no magnetic
moments
in these compounds.
The
same conclusion
can be drawn for the whole concentration
range; the Mn magnetic moment is less
than 0.1 pa but above a critical number
of Mn
neighbours it affects strongly the magnetic moment
of Fe leading to the disappearance
of magnetism.
A more detailed analysis of the hyperfine field data
will be performed to obtain the nearest neighbourhood dependence
of the iron magnetic moments.
The absence of Mn magnetic moments is quite
surprising
and it is different
from the magnetic
behaviour of Co in the same systems [5, 71.
This work forms part of the research program of
the Foundation
for Fundamental
Research
on
Matter (FOM), with financial
support from the
Netherlands
Organization
for the Advancement
of
Pure Research (ZWO).
Fig. 2. Concentration
dependence
of the average transition
metal moment (black circles) and the average iron hyperfine
field (empty circles) at 0 K: (a) (Fe,_,Mn&B
(the ji-r,, data
are taken from [I]); @) (Fe, _xMn,),Y.
kOe/Mn
atom in (Fe,_,Mn,),Y.
No hyperfine
field splitting was observed in the (Fe0,2,,Mn,,s0)2Y
compound.
It has been shown [5] from combined NMR and
Mossbauer investigation
of the (Fe, _,Mn,),B
system that the average iron hyperfine
field and
average iron magnetic - moment is strictly proporThe proportionaltional to each other: H,, = apFe.
ity constant was a = 130 kOe/p,.
A similar proportionality
was observed [6] in Y-Fe compounds
between zr, and fire with a slightly different proportionality
constant:
a = 145 kOe/pa.
Extrapolating
this proportionality
of H,, and
,iiFe for the (Fe,_,Mn,),B
and (Fe,_,Mn,),Y
Note added in proof. The average hyperfine fields
of “Mn in (Fe,,,,Mn&
B and (Fe,,Mn,,),Y
are
about 190 and 125 kOe, respectively,
according to
preliminary
NMR measurements
(Le Dang Khoi;
Institut d’Electronique
Fondamentale,
Orsay). Also
recent polarized neutron measurements
(M. J. Besnus) indicate the existence of magnetic moments
at Mn in (Fe,Mn),Y.
References
[l] M. C. Cadeville, Ph.D. Thesis, Universitk
Louis Pasteur,
Strasbourg,
France (1965); M. C. Cadeville and A. J. P.
Meyer, C. R. Acad. Sci. (France) 255 (1962) 3391.
[2] D. Givord, F. Givord and R. Lemaire, J. de Phys. 32 (1971)
Cl-668; K. K. J. Buschow and R. P. van Stapele, J. de Phys.
32 (1971) Cl-672.
[3] K. H. J. Buschow and R. C. Sherwood,
J. Appl. Phys. 49
(1978) 1480.
[4] G. Hilscher and H. Kirchmayr,
J. de Phys. 40 (1979) C5- 196.
[5] M. C. Cadeville and I. Vincze, J. Phys. F. 5 (1975) 790.
[6] P. C. M. Gubbens, J. H. F. van Apeldoorn
A. M. van der
Kraan and K. H. J. Buschow, J. Phys. F 4 (1974) 921.
[7] M. G. Luijpen, P. C. M. Gubbens, A. M. van der Kraan and
K. H. J. Buschow, Physica 86-88B (1977) 141; E. BUIXO,
Solid State Commun. 25 (1978) 825.