VoLume 38A, number 7
PHYSICS LETTERS
GIANT
27 March 1972
HYPERFINE
FIELD AT THE ANTIMONY
IN T H E H E U S L E R - A L L O Y
Pd2MnSb
SITE
L. J. SWARTZENDRUBER
Institute for Materials Research, National Bureau of Standards, Gaithersburg, Md. 20760, USA
and
B. J. EVANS
Department of Geology and Mineralogy, University of Michigan, Ann Arbor, Michigan 48102, USA
Received 28 January 1972
The magnetic hyperfine field at 121Sb in Pd2MnSb has the anomalously large value (at 100 K)
of ±579 ±5kG. In the closely related compound PdMnSb we find ±302 ±5kG, similar to other
ferromagnetic intermetallics containing Mn and Sb.
The f e r r o m a g n e t i c (T c = 247 K) H e u s l e r c o m pound Pd2MnSb has the L21 s t r u c t u r e , with a
magnetic m o m e n t of 4.4 g B p e r f o r m u l a unit,
confined to the Mn atom [1-3]. We find that the
121Sb hyperfine field in Pd2MnSb is much l a r g e r
in magnitude than any Sb hyperfine field reported
to date. This giant hyperfine field is much l a r g e r
than expected on the b a s i s of p r e v i o u s m e a s u r e m e n t s of Sb and Sn hyperfine fields in H e u s l e r and
other alloys. The Sb hyperfine field in the closely
r e l a t e d alloy PdMnSb ( f e r r o m a g n e t i c , T c = 500 K,
C1 b s t r u c t u r e [4]) i s found to be within the n o r m a l
r a n g e of e x p e r i e n c e .
Hyperfine fields and i s o m e r shifts were m e a s u r e d at 100 K u s i n g the 121Sb M~ssbauer effect.
The s p e c t r o m e t e r was c a l i b r a t e d u s i n g the h y p e r fine field value [5,6] of +291 kG for Sb in NiMnSb
at 100 K. I s o m e r shifts were m e a s u r e d with r e spect to an InSb a b s o r b e r at 100 K. The compounds were p r e p a r e d by a r c m e l t i n g in a T i gettered a r g o n a t m o s p h e r e , followed by a 48 hr
anneal at 1070 K and slow cooling. Metallo-
graphic a n a l y s i s showed each s a m p l e to be p r e dominantly single phase, with l e s s than about 5%
of an u n d e t e r m i n e d second phase detected at
g r a i n boundaries. X - r a y a n a l y s i s showed that
both alloys were cubic, with the a p p r o p r i a t e
s u p e r l a t t i c e l i n e s expected for the L21 (Heusler)
and C1 b s t r u c t u r e s . The m e a s u r e d lattice constants (table 1) a r e in good a g r e e m e n t with p r e viously reported values [1,4].
The MSssbauer s p e c t r a of Pd2MnSb, PdMnSb
and NiMnSb are shown in fig. 1. The solid l i n e s
a r e least s q u a r e s fits to the s p e c t r a a s s u m i n g a
single value of magnetic hyperfine field. The
m e a s u r e d hyperfine fields, linewidths and i s o m e r
shifts a r e given in table 1. The value of H n for
Pd2MnSb , extrapolated to 0 K by using the magn e t i z a t i o n c u r v e [2], is 609 kG, much l a r g e r than
the highest Sb magnetic hyperfine field found to
date [7] of 352.5 kG in MmSb.
The c o n s i d e r a b l e P d - S b d i s o r d e r reported [2]
for Pd2MnSb is c o n s i s t e n t with the single valued
hyperfine field found here if it is postulated that
Table 1
Comparison of Pd2MnSb, P d M n S b and NiMnSb. MSssbauer effect data were obtained at 100 K. Isomer shifts are
t
given with respect to an InSb absorber at 100 K. Lattice constants, ao, were measured at 300 K.
Compound
aO
(nm)
Tc
(K)
Hn
(kG)
r
(mm/sec)
Isomer shift
(mm/sec)
(± 5)
(± 0.2)
(± 0.2)
247 [2]
500 [4]
720 [11]
±579
±302
+291 [5]
(~-0.001)
Pd2MnSb
PdMnSb
NiMnSo
0.6419
0.6235
0.5913
4.8
3.5
3.1
1.1
0.7
1.4
511
Volume 38A, number 7
PHYSICS
27 March 1972
Table 2
Comparison of the antimony site hyperfine field coupling constants in Heusler-type alloys and in MnSb, derived from the saturation moments and 0 K Sb hyperfine field.
Pd z MnSb
l,-.
LETTERS
Derived
hype rfine field
coupling constant
(kG/~t B)
(per formula unit)
Pd MnSb
Ferromagnetic
saturation
Compound Structure
moment, (~tB)
(per formula unit)
Pd2MnSb
L21
4.4 [2]
138
(c)
Ni2MnSb
L21
3.6 [12]
56
NiMnSb
PdMnSb
C1b
4.0 [13]
77
NiMnSb
C1 b
3.8 [12]
7~
MnSb
B81
3.3 [14]
107
(b)
t,-
tt-
Ao-
o
;o io
VELOCITY
io
(mrn/sec)
Fig. 1. 121Sb MSssbauer effect absorption s p e c t r a at
100 K. In each case the solid line r e p r e s e n t s a least
squares fit to a single magnetic hyperfine field. The
zero of velocity r e p r e s e n t s the center of an InSb abs o r b e r at 100 K.
t h e Sb f i e l d i s n e a r l y the s a m e f o r an Sb on a P d
s i t e a s f o r an Sb on an Sb s i t e . A s i m i l a r b e h a v i o r h a s b e e n r e p o r t e d [8] f o r the Ni h y p e r f i n e
f i e l d in N i 2 M s S n , w h e r e the Ni f i e l d i s r e l a t i v e l y
unchanged by Ni-Sn disorder. The excess linewidth for Pd2MnSb (table i) could be attributed to
the disorder and allows a distribution in hyperfine fields of approximately ±20 kG centered
around the nominal value of 579 kG.
The great difference in the Sb magnetic hyperfine field between Pd2MnSband PdMnSbis in
contrast to previous results [5] for the isoelectronic L21 and C1b structures Ni2MnSband
NiMnSb, which both have nearly the same magnitude (and the same positive sign, ~ +300 kG)
for the Sb field. It is further interesting to note
that the field of Sn in Pd2MnSn(+48kG[9]) is
lower in magnitudethan that of Sn in Ni2MnSn
(+ 93 kG[10]), whereas the field found here for
Sb in Pd2MnSb (+ 579 kG) is much higher in magnitude than that for Sb in Ni2MnSb (+302 kG[5]).
Since most of the signs have not yet been determined, the direction of these changes in field
values cannot be compared.
In table 2 derived antimonysite hyperfine
field couplingconstants for a number of intermetallic compounds are compared. An explanation of the enhanced couplingin Pd2MnSbbased
on differences in the local charge density at Sb
does not appear tenable since the 121Sb isomer
shift in Pd2MnSbis well within the range of
values observed for other Sb Heusler alloys.
512
A p o s s i b l e e x p l a n a t i o n m i g h t be t h a t the P d a t o m s
in P d 2 M n S b a t t a i n a s m a l l m o m e n t . T h i s s m a l l
P d m o m e n t m i g h t s e r v e to e n h a n c e the h y p e r f i n e
f i e l d t r a n s f e r to t h e Sb a t o m s . H o w e v e r , in
Co2MnSn , w h e r e t h e Co i s k n o w n to c a r r y a m a g n e t i c m o m e n t , t h e r e i s no s u c h e n h a n c e m e n t .
T h e Sn h y p e r f i n e f i e l d i s + 1 0 7 k G [ 1 5 ] , w h i c h i s
only s l i g h t l y g r e a t e r t h a n the 93 kG [10] f o r Sn
in Ni2MnSn. A f i r m e x p l a n a t i o n f o r the g i a n t
h y p e r f i n e f i e l d in P d 2 M n S b i s not r e a d i l y a p p a r ent (but m i g h t b e r e l a t e d to the u n u s u a l p r e s s u r e
d e p e n d e n c e of T c [ 16]).
T h e a u t h o r s t h a n k D r . R. E. W a t s o n and D r .
L. H. B e n n e t t f o r u s e f u l c o m m e n t s .
RCfC~'CnCCS
[]l P - J . Webster and R. S. Tebb[e, J. Appl. Phys. 39
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