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MAGNETIC AND ELECTRONIC PROPERTIES OF RARE EARTH-RICH METALLIC GLASSES
G. Hadjipanayis, S. Cornelison, D. Sellmyer
To cite this version:
G. Hadjipanayis, S. Cornelison, D. Sellmyer. MAGNETIC AND ELECTRONIC PROPERTIES OF
RARE EARTH-RICH METALLIC GLASSES. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-
642-C8-645. �10.1051/jphyscol:19808161�. �jpa-00220262�
JOURNAL DE PHYSIQUE CoZZoque C8, supplement au n08, Tome 41, a o c t 1980, pageC8-642
G. Hadjipanayis, S.G. Cornelison and D.J. Sellmyer
BehZen L a b o r a t o r y o f P h y s i c s , U n i v e r s i t y of Nebraska, LincoZn, Nebraska 68588, U.S.A.
Abstract.- The magnetic and electrical properties of erbium-rich metallic glasses are presented.
Magnetic ordering has been observed around 15 K. Below the ordering temperatures a strong local anisotropy develops causing high coercive fields and lack of saturation. The resistivity changes drastically at the ordering temperature and either increases or decreases. The negative temperature coefficients or resistivity at room temperature are explained with the extended Ziman theory. The relationship between the observed kinks in the resistivity curves and the low temperature spin correlations are discussed.
INTRODUCTION ( i i i ) Below t h e o r d e r i n g t e m p e r a t u r e a l a r g e mag- The magnetic p r o p e r t i e s o f t h e non S - s t a t e n e t i c a n i s o t r o p y develops c a u s i n g h i g h c o e r c i v i t y r a r e - e a r t h amorphous m a t e r i a l s can be d i s c u s s e d by and l a c k o f magnetic s a t u r a t i o n ( F i g . 1 ) . ( i v ) t h e l o c a l random a n i s o t r o p y model [I]. The balance S t r o n g t e m p e r a t u r e dependent magnetic a f t e r e f f e c t s between magnetic a n i s o t r o p y and exchange i n t e r a c - appear a t 1 i q u i d he1 ium temperatures, s u g g e s t i n g a t i o n s causes a d i s p e r s i o n o f t h e moments and p r o - thermal a c t i v a t i o n process.
duces t h e known "speromagnetic" (no n e t moment) o r
I
I I I I I I I I1
"asperomagnetic" ( n e t ,moment) s t a t e s [2].
I n t h i s s t u d y we p r e s e n t t h e magnetic and t r a n s p o r t p r o p e r t i e s o f s e v e r a l r a r e - e a r t h r i c h
m e t a l 1 i c g l a s s e s . I n p a r t i c u l a r we i n v e s t i g a t e t h e
2 E 100 H
e f f e c t o f t h e Fermi r a d i u s k F on t h e r e s i s t i v i t y measurements and on t h e " s p i n s t r u c t u r e . " V a r i a - t i o n o f k F was a c h i e v e d by a l l o y i n g erbium w i t h d i f f e r e n t t r a n s i t i o n , n o b l e , and p o l y v a l e n t m e t a l s . An a t t e m p t was a l s o made t o r e l a t e t h e s p i n c o r r e - l a t i o n s w i t h t h e observed r e s i s t i v i t y k i n k s t h a t appeared a t t h e magnetic o r d e r i n g temperatures.
RESULTS
Amorphous samples were p r e p a r e d by t h e s p l a t c o o l i n g t e c h n i q u e . The e x p e r i m e n t a l t e c h n i q u e s have been d e s c r i b e d e l sewhere [3]. t ? a g n e t i c mea- surements on a l a r g e number o f r a r e - e a r t h r i c h amor- phous a l l o y s [3,4,5] show t h e f o l l o w i n g f e a t u r e s : ( i ) Some k i n d o f magnetic o r d e r i n g appears a t l o w temperatures. (ii) The magnetization o f t h e S- s t a t e I o n s (Gd) appears t o s a t u r a t e f a i r l y easy as e x p e c t e d ( F i g . 1 ) . I n t h e c a s e o f non S - s t a t e ions,
Fig. 1. Magnetization curves for R-Fe-B glasses at 4.2 K R e s i s t i v i t y measurements i n Er-Au g l a s s e s showed s e v e r a l k i n k s a t 1 ow temperatures ( F i g . 2).
A c o m p l e t e i n v e s t i g a t i o n o f t h e s e e f f e c t s has been undertaken i n t h i s s t u d y where we focus on erbium- based amorphous a l l o y s . The r e s i s t i v i t y c u r v e s o f s e v e r a l o f t h e s e a l l o y s a r e shown on F i g . 2. A d r a s t i c change i n r e s i s t i v i t y has been observed a t v e r y l o w temperatures (15 K ) . However t h e tempera- t u r e c o e f f i c i e n t s o f r e s i s t i v i t y a t 4.2 K and a t
Poom t e m p e r a t u r e change s i g n i n t h e sequence f r s m Er-Fe to Er-A1.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808161
I
I I I I100 200
T ( K )
F i g . 2 . E l e c t r i c a l r e s i s t i v i t y f o r e r b i u m - r i c h g l a s s e s .
The s u s c e p t i b i l i t y measurements a r e shown i n F i g . 3. A broad maximum has been observed i n a l l samples a t v e r y l o w temperatures. I n Er-Ga and Er- A1 glasses, t h e s u s c e p t i b i l i t y drops r a p i d l y below
t h e maximum and " f i e l d c o o l i n g " e f f e c t s a r e n o t i c e a b l e.
H i g h - f i e l d m a g n e t i z a t i o n measurements a r e shown i n F i g . 4 f o r Er-Ga. Flagnetic s a t u r a t i o n has n o t o c c u r r e d even a t f i e l d s up t o 8 0 kOe. A r o u g h e x t r a p o l a t i o n o f t h e h i g h - f i e l d p o r t i o n o f t h e mag- n e t i z a t i o n c u r v e a t 4.2 K r e s u l t e d i n a v a l u e o f t h e spontaneous moment F.lo = 122 emu/g.
F i g u r e 5 shows t h e l a r g e c o e r c i v e f i e l d s w h i c h develop below t h e o r d e r i n g t e m p e r a t u r e s . I n Er-Au
20
406
0T ( K )
F i g . 3. M a g n e t i c s u s c e p t i b i l i t y f o r e r b i u m - r i c h g l a s s e s (H= 700 Oe)
F i g . 4. 1 4 a g n e t i z a t i o n c u r v e s f o r (ErgOGa20) g l a s s
and Er-Ga t h e c o e r c i v i t y remains f a i r l y c o n s t a n t between 1 0 and 20 K s u g g e s t i n g a quantum mechanical t u n n e l i n g i n t h i s range [6]. For t h e o t h e r two a1
-
l o y s t h e s u b s t a n t i a l i n c r e a s e i n c o e r c i v i t y which i s observed below 1 0 K i s a s s o c i a t e d w i t h thermal processes.
Metamagnetic b e h a v i o r has been observed i n
C8-644 JOURNAL DE PHYSIQUE
Er-Au and Er-Ga i n t h e temperature range o f 30-60K.
This i s shown on Fig. 6 by t h e c o n s t r i c t e d hystere- s i s l o o p . I t suggests t h e presence o f a n t i f e r r o - magnetic i n t e r a c t i o n s which c o u l d be broken up by t h e a p p l i e d f i e l d .
F i g . 5. Temperature dependence of c o e r c i v i t y i n e r b i u m - r i c h glasses
H (kOe)
F i g . 6. H y s t e r e s i s loops i n (ErgOAu20) 90B1u glass DISCUSSION
I t i s e v i d e n t from t h e s u s c e p t i b i l i t y curves t h a t magnetic o r d e r i n g takes p l a c e around 15 K f o r a l l Er-based a l l o y s . The high-temperature suscep-
t i b i ' l i t y data were f i t t o a Curie-Ueiss l a w and M e f f per Er atom was found t o be 11 -0, 10 and 8 pB f o r t h e Er-Au, Er-Ga and Er-A1 glasses r e s p e c t i v e l y . The corresponding Curie temperatures were estimated t o be 6, 4 and 15 K r e s p e c t i v e l y , i n d i c a t i n g f e r r o - magnetic i n t e r a c t i o n s . The values o f peff d e t e r - mined appear t o be s l i g h t l y d i f f e r e n t than t h e ex- pected 9.5 pB.
Below t h e o r d e r i n g temperatures h y s t e r e s i s e f - f e c t s appear. The l a c k o f magnetic s a t u r a t i o n sug- gests t h e presence o f a h i g h magnetic a n i s o t r o p y . The zero f i e l d e x t r a p o l a t e d values o f t h e moment a r e about 1
T
gJpB i n d i c a t i n g an "asperomagnetic" o r - d e r i n g w i t h t h e moments spread o u t i n t o a hemi- s p h e r i c a l "fan".The Ziman t h e o r y and i t s extensions
171
a r e employed t o e x p l a i n the r e s i s t i v i t y measurements o f amorphous m a t e r i a l s . I n these t h e o r i e s t h e r e s i s t i v i t y i s given bywhere S(q) i s t h e s t r u c t u r e f a c t o r , v ( q ) i s t h e F o u r i e r t r a n s f o r m o f t h e pseudopotential o f a s i n g l e i o n o r t h e s i n g l e t - m a t r i x f o r t h e t r a n s i t i o n met- a l s and 2kF i s t h e diameter o f t h e Fermi sphere.
Because o f t h e q 3 f a c t o r , t h e i n t e g r a l i n Eq. (1) h e a v i l y weights those values o f t h e i n t e g r a n d near q = 2kF. Therefore t h e temperature dependence o f p f o l l o w s t h e temperature dependence o f S(q) near 2kF The f i r s t peak o f S(q), a t t h e p o s i t i o n q becomes
P'
l o w e r and broader as temperature increases. There- fore, t h e p o s i t i o n o f 2kF w i t h respect t o q w i l l
P determine t h e s i g n o f t h e h i g h temperature c o e f f i - c i e n t o f r e s i s t i v i t y Bh. I n Er-Fe, Er-Co and Er-Ni glasses
Bh
i s negative. Thus according t o t h e Ziman t h e o r y[71
q = 2kF f o r these t h r e e glasses.P
This suggests t h a t t h e number o f conduction e l e c -
t r o n s i s t h e same f o r t h e t h r e e t r a n s i t i o n metals, s u p p o r t i n g t h e assumption o f Esposito e t a l . [8!.
However i n going from N i t o Ga, kF increases s i n c e t h e number o f conduction e l e c t r o n s increase. This suggests t h a t 2 k F > q which would be c o n s i s t e n t
P
w i t h a p o s i t i v e Bh as i s observed. These assump- t i o n s a r e confirmed e x p e r i m e n t a l l y . I n Er-Fe, 2 k F = 2.27
i
and q = 2.27i-'.
However i n Er-A1P
2kF = 2.44 i - l a n d q ~ 2 . 2 7
i-' .
P
Magnetic o r d e r i n g c o n t r i b u t e s an a d d i t i o n a l term t o r e s i s t i v i t y . Asomoza e t a l . [9] obtained t h e f o l l o w i n g expression f o r t h e r e s i s t i v i t y i n t h e ordered magnetic s t a t e :
p = a + bm(2kF) (2)
where t h e f i r s t term i s due t o independent s c a t t e r - i n g by each magnetic i o n , t h e second term i s due t o coherent exchange s c a t t e r i n g and m(2k ) i s t h e s p i n
F
c o r r e l a t i o n f u n c t i o n a t 2kF. T h i s f u n c t i o n i s given by
I f however an asperomagnetic o r d e r i n g i s assumed,
then
where p1 i s a parameter o f l o c a l magnetic o r d e r and Sll (q) i s t h e s t r u c t u r e f a c t o r o f t h e magnetic ions. As k F increases, Sll ( q ) and t h e r e f o r e p de- creases (Eq. 2 ) . T h i s was observed on Fig. 2 where t h e 1 iq u i d he1 ium temperature c o e f f i c i e n t o f r e s i s - t i v i t y B1 changes from n e g a t i v e t o p o s i t i v e i n going from Er-Fe t o Er-A1 glasses.
The anomaly i n p(T) a t 80 K observed i n Er-Au and Er-Ga may be due t o l o c a l a n t i f e r r o m a g n e t i c s p i n c o r r e l a t i o n s as expressed i n t h e magnetiza- t i o n o f Fig. 6. The antiferromagnetic i n t e r a c - t i o n s may a r i s e from s u b t l e l o c a l s t r u c t u r a l ef- f e c t s . T h i s a l s o c o u l d g i v e r i s e t o t h e c o e r -
c i v i t y anomalies observed i n Er-Au and Er-Ga i n t h e temperature range o f 30 t o 60 K.
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