Supported by the National Science Foundation and Indiana Universit

Black, R.

Blue, James W.

DeMarco, Mike

ElFazani, Mohamed

Jha, S.

Julian, Glen M.

Scholten, P.D.

Snyder, John W.

Vaiude, Devendra

Ward, T.E.

English

IUScholarWorks

HYPERFINE INTERACTIONS 
HYPERFINE MAGNETIC FIELD MEASUREMENTS I N  FERROMAGNETIC CHALCOGENIDE SPINELS AND 
HEUSLER ALLOYS BY TDPAC TECHNIQUE 
S. Jha ,  Mohamed ElFazani, Mike DeMarco, and Devendra Vaiude 
University of Cincinnati, Cincinnati, Ohio 45222 
Glenn M. J u l i a n ,  P.D. Scholten,  John W. Snyder, and R.  Black 
M i d  University, Oxford, Ohio 45056 
James W .  Blue 
NASA-Leuis Research Center, CZeveZand, Ohio 441 35 
T.E. Ward 
Indiana University Cy cZotron Faci Zity , BZoomington, Indiana 4 7405 
I n  t he  year under review, we have s t a r t e d  super- t ransfer red  hyperf ine  i n t e r a c t i o n .  The TDPAC 
measurements of t h e  hyperf ine  magnetic f i e l d  i n  technique o f f e r s  a  very powerful and convenient tech- 
ferromagnetic s p i n e l s  XCr2Y4 where X can be Cu, Zn, Cd, nique of in t roducing  extremely d i l u t e  r ad ioac t ive  i m -  
and Hg and Y can be S, Se, and Te, The magnetic moment p u r i t i e s  and thus enabling t h e  measurements of t he  
is ca r r i ed  only by the  C r  ions  (p=3 Bohr Magneton). hyperfine f i e l d s  a t  a  v a r i e t y  of probes. We have thus 
The l a t t i c e  parameter is  about 10 g. The s p i n e l  f a r  measured the  temperature v a r i a t i o n  of t he  hyper- 
111 
s t r u c t u r e  is  shown i n  Fig.  1 where t h e  B s i t e s  a r e  f i n e  f i e l d s  a t  Cd i n  CdCr2S,, ( ~ ~ ' 8 4  .5OK) , 
exclus ive ly  occupied by cr3" ions ,  and the  A s i t e s  by CdCr2Seq (Tc=129 .~OK)  and Cue ggCd 01Cr2Te4 (~,=365OK) . 
Cd o r  Cu ions .  The cr3+ ion  moments a r e  a l igned The s t u d i e s  of t he  hyperf ine  magnetic f i e l d  i n  
p a r a l l e l  i n  ferromagnetic s p i n e l s  through t h e  i n t e r -  Heusler a l l o y s  have been continued. The s t u d i e s  have 
mediary of t he  chalcogen p e l ec t rons .  The hyperf ine  included the  Heusler a l l o y s  of t he  type X2MnY wi th  
f i e l d  a t  Cd and Cu a r e  brought about by t h e  excess L21 s t r u c t u r e  and of t h e  type XMnY wi th  C l b  s t r u c t u r e .  
sp in  po la r i za t ion  e l ec t ron  dens i ty  a s  a r e s u l t  of t h e  The s ign  of t he  hyperf ine  f i e l d  a t  t h e  probe s i t e  is 
B - SITES (Cr) 
A -  SITES (CU ,Cd) 
0 ANIONS (S,  Se,  Te) 
Figure 2. Positions of cations and anions i n  the 
spine 2 structure . 
a very i-mportant p iece  of da ta .  The s ign  of t he  f i e l d  
s i g n i f i e s  t he  e l e c t r o n  sp in  po la r i za t ion  d i r e c t i o n  a t  
t he  probe s i t e .  The magnetic f i e l d  a t  t he  probe s i t e  
is  p o s i t i v e  i f  t he  f i e l d  is p a r a l l e l  t o  t he  ex t e rna l ly  
appl ied  f i e l d ,  i t  i s  negative i f  i t  is  a n t i - p a r a l l e l .  
The s ign  of t he  hyperf ine  magnetic f i e l d  is 
determined a s  described below. The source i n  t he  
Heusler a l l o y  i s  placed i n  an ex t e rna l  magnetic f i e l d  
of about 4 KG, the  f i e l d  being perpendicular  t o  t he  
plane of t he  de t ec to r s  which a r e  placed a t  135O. The 
coincidence r a t e  a s  a funct ion  of the  angle between 
the  de t ec to r s ,  8 ,  t he  time i n t e r v a l  between the  
a r r i v a l  of the  s t a r t  and the  s top  gamma-ray pulses ,  
fine field has been determined for Ni2MnGa, Ni2MnIn, 
' 111 
-.I04 Cd(Rh,Mn Pb) 1 40 4 -1 
Figure 2. Perturbed angular correk t ion  ~ i t h  
L m o r  oscCZZations for 9 9 ~ h  i n  Rh2MnPb. 
t, and the magnetic field, B, is given by 
W(O ,t,B)=exp(-t/r) [l+a2 cos 2 (0w,t) ] 
where w,= Larmor angular frequency 
w, =-gp,~/K . 
For 0 = -135O, a2 = -0.2, and a negative g-factor for 
1 1 1  
Cd, ~(-135O,t,-~) = exp(-t/~)(l+0.2 sin 2 w, t) 
and W(-135O,t, +B) = exp (-t/-r) (1-0.2 sin 2 w,t) . 
The shape of the perturbed decay curve at t=O deter- 
mines the sign of the field. The sign of the hyper- 
Cu2MnIn and Cu CdO .01Cr2Te~. In Table I, the 0.99 
1 1 1  
hyperfine magnetic fields at Cd at different 
temperatures are given for Rh2MnGe, Rh2MnSn and 
Rh2MnPb. The field values for Rh2MnPb are derived 
from the data shown in Fig. 2. The hyperfine field 
normalized at T=77OK is plotted against TIT in Fig. 3. 
1 1 1  
Table I. Hyperfine fields measured at Cd sites in 
various alloys 
Alloy B CkG) T(OK) 
Rh2MnGe 188 + 6 7 7 
160 3 293 
Rh2MnSn 189 + 5 7 7 
113 + 5 293 
33 + 3 373 
Rh ,Mn~b 143 + 2 7 7 
114 5 2 200 
84 + 2 273 
53 + 1 293 
Figme 3. Hyperfine fields normaZized a t  T=77OK and 
plotted against T/Tc for 9 9 ~ h  i n  Rh,bhGe, Rh2MnSn 
and Rh2MnPb. 
Table 11. Hyperf ine fields measured at l 1  '~d sites 
in various alloys 
The experimental data deviate significantly from the 
Brillouin function for J=5/2. The hyperfine fields 
11 1 
at Cd in PtMnSb, NiMnSb and PdMnSb at various 
temperatures are given in Table 11. The comparison 
with the Brillouin function similar to that in Fig. 2 
is given in Fig. 4. The hyperfine field data for 
Ni2MnGa, Ni2MnIn, Cu2MnIn, and Au2MnIn are given 
in Table 111. The comparison with the Brillouin 
function is given in Fig. 5. The hyperfine field 
direction at lllcd in Ni2MnGa is shown to be negative. 
Our experimental data for '' l1n(cdcr2se4) at 
4 .  ~OK, 77OK, and 293'~ yielded the hyperfine field values 
given in Table TV and was also shown to be positive. 
These data confirm the results of NMR studies of these 
spinels. 
Alloy B (kc) T (OK) 
P tMnSb 166 + 4 7 7 
NiMnSb 
111 
Table 111. Hyperfine Magnetic Field at Cd sites 
in Heusler Alloys X2MnIn and X2MnGa 
PdMnSb 260.92 4.5 9 0 
Alloys Tc (OK) B (KG) T(OK) 
Figure 4.  BriZZouin function compared with the 
hyperfine fields measured for l l led i n  PtM*rSb md  
NiMnsb. 
B (TI 11 1 
- M U )  Table IV. Hyperfine Magnetic Field at Cd Probe 
B (771, , M(77) in Chalcogenide spinels 
Fi.gw?e 5. Comparison o f  the Brillouin function 
with the hyperfine fields measured for l l l ~ n  i n
%MnIn, Ni ,MnCa and Ni2MnIn. 
1.0 
.75 
.50  
.25 
0 
.25 .50 .75 1.0 
- -Ao+- - 
A 
,- 'o\ - 
O: 
- 
A Cu2MnIn 
- O Ni2MnGa '\ - 
+ Ni2 MnIn 
I I I 
1.0 Alloys Tc (OK) B (KG) T (OK) 
CdCr2S4 84.5 85.5+1 
.75 7 7 
168 22 4.2 
-.50 CdCr2Se4 129.5 104 *1 7 7 
132 +I 4.2 
2 5  cu 99~d. 01Cr2Te4 365 98.5 +I 7 7 
79 -+I 195 
- 0  44.5 +1 293 


Hyperfine Magnetic Field Measurements in Ferromagnetic Chalcogenide Spinels and Heusler Alloys by TDPAC Technique

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Hyperfine Magnetic Field Measurements in Ferromagnetic Chalcogenide Spinels and Heusler Alloys by TDPAC Technique

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