The enhancement of Fe hyperfine field with Mn addition in a
Fe(80−x−y)NiyMnxB12Si8 alloys
Nirupama Sharma, A. K. Nigam, Shiva Prasad, S. N. Shringi, Girish Chandra et al.
Citation: J. Appl. Phys. 69, 5364 (1991); doi: 10.1063/1.348030
View online: http://dx.doi.org/10.1063/1.348030
View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v69/i8
Published by the American Institute of Physics.
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The enhancement of Fe hyperfine
in a-Fe(~o--x-~~NiyMn,B,,Si, alloys
field with Mn addition
Nirupama Sharma
Department of Physics, Indian Institute of Technology, Powai, Bombay, (400076) India
A. K. Nigam
Tata Institute of Fundamental
Research, Homi Bhabha Road, Bombay, (400005) India
Shiva Prasad and S. N. Shringi
Department of Physics, Indian Institute of Technology, Powai, Bombay, (400076) India
Girish Chandra
Tata Institute of Fundamental Research, Homi Bhabha Road, Bornboy, (400005) India
R. Krishnan
Laboratoire de Magnetisme, C. N. RS., 9219.5 Meudon Cedex, France
Amorphous Fecgo- x -u) Ni ,M n,BlaSis alloys with O<x<l and 2O<y<50, have been studied
using Mijssbauer spectroscopy at 77 K. It has been found that the sharp rise in the
alloy magnetic moment for certain specific values of x and y can be best explained if both pi+
for those particular samples. However, the increase in PNi ( -80%) is
and PNi increase
much larger than that in &e ( - 5%).
Ii. EXPERIMENTAL
I. INTRODUCTION
The presence of Mn in amorphous ferromagnetic alloys gives rise to many interesting features as far as magnetic properties are concerned. For example, in a-Fe-M
alloys (Mmetalloid),
the addition of Mn gives rise to a
large decrease in the magnetic moment, an effect which is
invariably found when early 3d transition metals (TM) are
included in Fe-based amorphous alloys.’ However, in Cobased alloys the addition of Mn does not cause any decrease in the magnetic moment and shows a rather small
increase.L This behavior is contrary to the addition of other
early 3d transition metals like Cr, in the same Co-based
alloys. In an Fe-N&M system containing about 50% Ni
also, the presence of Mn does not show any significant
decrease in the magnetic moment. On the other hand, it is
found that in a-Fe!~o_x_y~NiSMnxB1ZSi8, for y=40 and
45, the presence of around 0.2%-0.5% of Mn becomes
responsible for a sharp increase (-20%)
of the magnetic
moment.3 This phenomenon is not clearly understood.
Since the concentration of Mn is very small in these alloys,
the increase in the alloy magnetic moment has to be attributed to an increase in magnetic moment of either or both
Fe and Ni. But it is not clear which of these moments is
actually increasing.
On the basis of a room-temperature Miissbauer study,4
Krishnan et aL3 predicted that the sharp increase in the
magnetic moment of a-Fe(sa _ L _ ,+Ni,MnXBr2Si8 for a certain small concentration of Mn, could be caused by an
increase of both the Ni magnetic moment (PNi) and the Fe
magnetic moment (pi+). In this paper, we report
the low-temperature
(77 K) Mossbauer study on
Ni
n,B&Sis
(with O<x<l and 2Oc;y<50,
a-F%0 - x-y)
yM
expressed in at. % ) . An attempt has been made to combine
this data with the magnetic-moment results in order to
yield information about pFe and pNi*
5364
J. Appl. Phys. 69 (8), 15 April 1991
DETAILS
The alloys were prepared by the melt-spinning technique. The samples were in the form of ribbons about 3
mm wide and nearly 35 pm thick. Miissbauer measurements were carried out in the standard transmission geometry, at 77 K. The source used was 57Co (in Rh matrix). A
natural Fe absorber was used for calibration.
The analysis of the spectra was done using Window’s
Fourier series method.5 An H,,,,, of 400 kG was used. The
intensity ratio of the second to the third line, linewidth of
the subspectra, quadrupole splitting, and the isomer shift
gradient were the parameters optimized to give minimum
x2. The details of the fitting procedure are similar to those
in our earlier publication.’
Ill. RESULTS
AND DISCUSSION
The Mijssbauer spectra and the corresponding P(H)
for some of our samples, viz., y=45 and x=0, 0.2,0.5, and
1.0, are shown in Fig. 1. The linewidth at half-maximum of
the hyperfine field distribution P(H) ranges between 35-45
kG. These values are comparable to the values obtained by
Whittle and Stewart,7 for a-Fess -,Ni,B,,
alloys. We do
not observe any bimodality in the P(H) curves which is
usually found in early 3d TM-containing alloys. However
the small Mn concentration in these alloys may not be
enough to give rise to this effect.
Figure 2 shows the hyperfine field values, obtained
from P(H), as a function of Ni concentration for x=0.
From the figure one finds that the average hypertine field
H,, shows a broad maximum as a function of Ni concentration. This result is somewhat surprising noting the fact
that the addition of Ni always caused reduction in the
magnetic moment of the alloy;3’8 for example, the alloy
magnetic moment drops by -25% as Ni concentration
increases from 20 to 40 at. %.8 Mossbauer studies in FeNi-M alloys, on the other hand, do not indicate such a
0021-8979/91/085364-03$03.00
@ 1991 American
Institute
of Physics
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5364
[FeBO-x-y
bilk* b:-xj
E:2
S:a
-
77~
0
0
0
0.06
0 y=3!
0.02
e
- 0.02
e
,my=4(
0.06
0.02
A
^-
- 0.02 b
A
A
Ay=4!
A
A
, , c
A
I,,
-20 KG
0.0
0.2
Mn
Fe 80-x-y
FIG. 1. Mksbauer spectra and hyperfine field distributions
Fe~s0-r-ylNi~nnB12Si8
alloys at 77 K.
AyY=5l
0.6
-----ik
CONCENTRATION, x
Niy Mn,‘12 si8
of a-
FIG. 3. Average hyperfme field, H,, vs Mn concentration.
rapid fall in Fe hyperfine field. In fact, Ha, is found to be
reasonably constant within 5% over a large concentration
range of Ni on the Fe-rich side.8 Whittle and Stewart, on
the other hand, have found a broad maximum in H,,, similar to that observed by us, in FegS-xNixBIS alloys and
have discussed this effect in detail7 The presence of such a
maximum with Ni concentration may be dependent on the
system studied; yet, it is clear that the hyperfine field drops
x = 0.0
27oi-----
1
260
Y
0
0
0
0
0250
2201
15
I
I
,
I
I
I
I
20
25
30
35
40
45
50
Ni
Fe8()-x-y
CONCENTRATION,
Niy
Mn,
812
55
y
SC3
FIG. 2. Average hyperfine field, H,, vs Ni concentration, for x = 0.
5365
J. Appl. Phys., Vol. 69, No. 8,15
April 1991
much more slowly as compared to the magnetic moment of
the alloy. The hyperfine field is usually given by
&=AcLF~
(1)
+ BIA
where ,u is the average magnetic moment of the alloy. In
our alloys, for y=35-45, the hyperiine field is constant
within the experimental accuracy (Fig. 2), while ,u is
found to decrease by 30%.3 fi values have been measured
at 4.2 K; Hay is, however, at 77 K. But at T=77 K,
T/T, is very small, i.e., less than 0.12, so we can assume
that the departure from the saturation H,, value will be
nearly identical for all the samples, such that it can be
taken care of by a slightly reduced value of A. Hence Eq.
( I) would indicate that if A and B are nearly constant over
this concentration range, the Bp term is expected to have a
smaller effect on the Ha, than A/Q+. This would indicate
that in the present series, the presence of Ni up to -45
at. % does not cause any decrease in ,&i+.
Figure 3 shows the variation of Ha, as a function of X.
We observe that H,, goes through a maximum around
x=0.2-0.5, for y=35, 40, and 45. For y=40 and 45, the
rise in the Ha, values is observed for the same samples that
showed an enhancement in the alloy magnetic moment.
But this increase is only 4%-5% as against the 20% increase observed in p. For the present system, p per formula
unit can be expressed as
Y= I(80 --x --Y)PF~
+ YpNi +
~~~n1/100-
(2)
Thus, the increase in J.Lcould be because of an increase in
any of the three moments, viz., PM,,, ,++, and PNi. Krishnan et aL3s9 have used the nuclear-magnetic-resonance
(NMR) spin-echo technique to estimate ,u~ They found
Sharma
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et a/.
5365
that this moment is quite large ( -3.3 ,LL~),for all values of
x in the present series. But since the concentration of Mn is
quite small in these alloys, this alone cannot be responsible
for the sharp increase in p. Hence, it becomes necessary to
postulate that either or both ,+e and I-LNiincrease with the
addition of Mn. If we assume that it is only PNi that is
increasing with x, keeping &Q constant, we can fit Eq. ( 1)
to the Ha, vs p data. This would be a straight line under the
present assumption. In this way we can obtain the values
for B and A,L+~. If we take a value of p&-2.1
PB and
pMn = 3.3 PLg,we Can CalCUlate PNi, from Eq. (2) which iS
found to vary from 0.39 to 0.91 pB as x goes from 0 to 0.5,
for y=40 while A and B are found to be almost 80 and 96
kG/p,, respectively. This shows a rather high value of
PNi when compared to crystalline alloys. On the other
hand, if we try to assume that it is only pFe that increases
with x, then using the procedure similar to the one adopted
by Prasad et uZ.,‘~ one can calculate j+j, A, and B, which
all turn out to be unrealistic.
In our earlier discussion on Ha, as a function of y, we
noted that the Bp term could be much smaller than A,LLF~in
Eq. ( 1). Hence .we tend to make an assumption that
H,, = A,LL~,.Such an assumption has been used quite commonly in the literature. ‘,* The value of A was taken to be
120 kG/pB, which is similar to the value usually found in
a large number of amorphous crystalline alloys.” Using
this value of A and the experimental value of H,,, one can
determine ,!+ and using this in Eq. (2), YNi can be obtained. These values are given in Table I. From this table
we find that both &+ and PNi show an increase for the
samples that exhibit enhanced magnetic moment. Also the
increase in PNi is much larger than that in ,+e. These values, specially /‘Ni, appear to be more realistic than the case
when pFe was assumed to be constant. We therefore feel
that the increase in the moment of the alloy is also partly
because of an increase in pFe.
As can be seen from Fig. 3, for y=50, no increase in
H,, was obtained. The present assumption would indicate
that ,$+ continuously decreases with x, for this value of y.
Hence it appears that the increase in pFe is caused only
5366
J. Appl. Phys., Vol. 69, No. 8, 15 April 1991
TABLE I. Mijssbauer and magnetic-moment data along with the calculated values of /+ and pm, for the a-Fe,,, _ I _ ,.,Ni@n,BlzSis alloys.
x at. %
y=40
0.0
0.5
1.0
y=45
0.0
0.2
0.5
1.0
f&v(=)
PW
~Fehd
pNi(pB)
255
265
25s
0.994
1.190
0.990
2.13
2.21
2.13
0.36
0.75
0.32
2.12
2.23
2.12
2.07
0.35
0.64
0.39
0.46
254
0.90
268
1.06
254
248
0.89
0.88
when a certain critical amount of Ni and Mn are present
together. The reason for this is, however, not clear.
ACKNOWLEDGMENT
The electron probe microanalysis of the samples by
Mme. Kommeluere is gratefully acknowledged.
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97, 199 (1986).
‘R. C. O’Handley and M. 0. Sullivan, J. Appl. Phys. 52, 1841 (1981).
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Proceedings of ICPMM, Poland, edited by W. Gorzkowski, H. Szymczak, and H. Lachowicz (World Scientific, Singapore, 1989).
‘A. Lagu, S. N. Shringi, A. K. Nigam, Girish Chandra, Shiva Prasad,
and R. Krishnan, Hyperfine Interactions 51, 1025 (1989).
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Krishnan, Solid State Commun. 54, 313 ( 1985).
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sM. Sostarich, S. Dey, P. Deppe, M. Rosenberg, G. Czjzek, V. Oestriech,
H. Schmidt, and F. E. Luborsky, IEEE Trans. Magn. MAG-17, 2612
(1981).
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ICPMM, Sendai, edited by M. Takahashi, S. Mackawa, Y. Gondo, and
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‘OS. Prasad, V. Srinivas, S. N. Shringi, A. K. Nigam, G. Chandra, and R.
Krishnan, J. Magn. Magn. Mater. (to be published).
” P. Panissod, J. Durand, and J. I. Budnick, Nucl. Instrum. Methods 199,
99 (1982).
Sharma
#al.
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5366