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Ferromagnetic properties of CoGa alloys with B2 structure
Volume 32A. number 3
FERROMAGNETIC
PHYSICS LETTERS
PROPERTIES
OF
Co-Ga
ALLOYS
29 June 1970
WITH
B2
STRUCTURE
Jo G. BOOTH and J. D. MARSHALL
Deparlrnenl of Pure and Applied Physics, Unieersily of SalfoJ'd, Salford 5, Lancs.. UK Received 22 May 1970
Cobalt-rich CoGa alloys having the ordered bcc (B2) structure are reported to be ferromagnetic. The magnetization and Curie temperatures are proportional to the square of the excess Co concentration.
R e c e n t m a g n e t i z a t i o n m e a s u r e m e n t s [1] on the o r d e r e d bcc (B2) a l l o y s of the CoAl s y s t e m have shown that the a l l o y s r i c h e r in cobalt than 50% a r e f e r r o - m a g n e t i c , f e r r o m a g n e t i s m being a s s o c i a t e d with the s u b s t i t u t i o n of cobalt a t o m s into the g a l l i u m lattice, producing defect or "antistructure ~ atoms. We r e p o r t h e r e m a g n e t i z a t i o n and s u s c e p t i b i l i t y m e a s u r e m e n t s on the r e l a t e d CoGa s y s t e m in which the B2 s t r u c t u r e is s t a b l e o v e r a w i d e r c o m p o s i t i o n r a n g e (44 to 66 % Co a p p r o x i m a t e l y ) . T h e s e a l l o y s have not p r e v i o u s l y been r e p o r t e d to be f e r r o m a g n e t i c . The m e a s u r e m e n t s w e r e made o v e r the t e m p e r a t u r e r an g e 4,2 to 300°K in f i e l d s up to 17 kOe using a v i b r a t i o n m a g n e t o m e t e r ( P r i n c e t o n App l i e d R e s e a r c h Corp) in which s p e c i m e n t e m p e r a t u r e s w e r e i n d i ca t e d by a c a l i b r a t e d c o p p e r constantan t h e r m o c o u p l e p l a c e d in c l o s e p r o x i m ity to the s a m p l e . The a l l o y s w e r e f a b r i c a t e d f r o m 4N8 cobalt r o d s and 5N g a l l i u m ingots by r e p e a t e d m e l t i n g in an a r g o n - a r c f u r n a c e . A f t e r m e l t i n g the a l l o y s w e r e c r u s h e d , s e a l e d in q u a r t z unde r vacuum, and a n n e a l e d at 830°C f o r 24 h o u r s with s u b s e q u e n t quenching into w a t e r . C h e m i c a l a n a l y s i s was p e r f o r m e d f o r cobalt content° X - r a y e x a m i n a t i o n showed only the p r e s e n c e of B2 l i n es and m e t a l l o g r a p h s did not r e v e a l the p r e s e n c e of a s e c o n d phase. A l l o y s r i c h e r in cobalt than 51% w e r e found to be f e r r o m a g n e t i c and C u r i e t e m p e r a t u r e s T c w e r e d e t e r m i n e d by plotting ~ 2 T a g a i n s t H/CrHT [2] to d e t e r m i n e the i s o t h e r m a l p ~ s s in g through the o ri g i n . It was noted that a l l o y s within 2 o r 3 p e r c e n t of the e q u i a t o m i c c o m p o s i t i o n w e r e u n s a t u r a t e d at 4.2 OK and 17 kOe. Fig° 1 shows p l o t s of ~T c and 4-(~o o (the i n s t r i n s i c m a g n e t i z a t i o n ) a g a i n s t cobalt c o n c e n t r a t i o n . A l i n e a r r e l a t i o n s h i p is e v i d e n t as was found f o r CoAl in [1], and the i n t e r c e p t at 50.7% Co is c l o s e to the c o m p o s i t i o n at which Co a t o m s e n t e r
•K½
,-J_,
..~ 52
54 56 Atomic Percent Cobolt
(¢rnu/glg
58
60
Fig. 1. Relationship between (a) ( T c and cobalt concentration and (b) ~/~oo and cobalt concentration for CoGa alloys. the Ga l a t t i c e [3]. The f e r r o m a g n e t i c p r o p e r t i e s can t h e r f o r e be a s s o c i a t e d with the f o r m a t i o n of cobalt a n t i s t r u c t u r e a t o m s in the g a l l i u m lattice. If we a s s u m e that only t h e s e a n t i s t r u c t u r e a t o m s have m a g n e t i c m o m e n t s a s s o c i a t e d with them in the CoGa B2 phase the r e s u l t s shown in table 1 c o l u m n s 5 and 6 a r e obtained. The m a g n e t i c m o m e n t p e r e x c e s s cobalt atom deduced f r o m the low t e m p e r a t u r e m a g n e t i z a t i o n m e a s u r e m e n t s ( f e r r o P x s Co ) and f r o m the slope of the inverse susceptibility versus temperature curve (para ~ x s Co ) a r e shown, The m o m e n t s obtained f r o m the f e r r o m a g n e t i c data a r e in a s i m i l a r r an g e to those o b s e r v e d f o r Co in CoAl a l l o y s [1]. Howe v e r those deduced f r o m the p a r a m a g n e t i c data a r e c o n s i d e r a b l y l a r g e r . Such a d i s p a r i t y m ay be o b s e r v e d f o r m a t e r i a l s which fall into the 149
Volume 32A. number
3
Saturation magnetization. netic moment per excess
At ~:,; Cobalt 52,5 53.9 54.4 56.6 58.2 60.6
Excess Ate,: Cobalt 1.8 3.2 3.7 5.3 7.5 9.9
PHYSICS
Table 1 Curie temperature, and magcobalt atom for CoGa alloys.
(~o o
Tc -I °K
e . m . u, g. 1.9 3.1 5.0 12.3 18.1 30,1
LETTERS
9 20 25 73 122 228
Para PXSCo (P'B) 1.2 1,1 I .5 2.7 2.8 3.5
Para PXSCo (~B) 7 6 6 6 6 8
29 June 1970
t i o n of t h e 59Co a n d 27A1 s i g n a l s f o r a Co50°5A149.5 a l l o y h a v e s u g g e s t e d t h a t s o m e l o c a l i z e d m o m e n t s e x i s t in t h a t a l l o y s y s t e m , a n d a l t h o u g h m e a s u r e m e n t s on Co r i c h a l l o y s h a v e not y e t b e e n m a d e i t i s p o s s i b l e t h a t s u c h a s i t u a t i o n o b t a i n s f o r the a l l o y s u n d e r d i s c u s s i o n here° References
c a t e g o r y of i n t i n e r a n t f e r r o m a g n e t s , e s p e c i a l l y if w e a k I41, but it s h o u l d b e m e n t i o n e d t h a t Van O s t e n b u r g e t al. [51 on t h e b a s i s of t h e o b s e r v a -
[1] S.R. Butler. J . E . H a n l o n a n d R . J . W a s i l e w s k i . J. Phys. Chem. Solids 30 (1969} 1929. [21 J . S . Kouvel and M . E . F i s h e r . Phys. Rev. 136A (1964) 1626. [31 K. Schubert. H,L. Lukas, H . - G . M e i s s n e r and S. Bhan, Z.Metallk. 50 (1959) 534. [41 E . P . Woh[farth. J. Appl. Phys.. 39 (1968) 1061. [5] D.O. Van Ostenburg. J . J . Spokas, C.H. Sowers and H.G. Hoeve. Phys. L e t t e r s 30A (1969) 130.
N O U V E L L E S R A I E S L A S E R I N F R A R O U G E S DANS LA V A P E U R DE B A R Y U M Ph. CAHUZAC Laboraloire
Airn~
Cotton
- C, N.R.S.
II -
91 O R S A Y - F r a n c e
Received 28 April 1970
New pulsed l a s e r actions have been obtained in barium vapor. Twenty infrared l a s e r lines have been observed in this vapor.
Dans la vapeur de baryun, nous avons observ~ en impulsions 20 nouvelles t a l e s l a s e r infrarougeso Cette ~tude fair suite ~t celle concernant les t e r r e s r a r e s [1,2]. La m~thode exp~rimentale utilis~e est celle d~j~t d4crite darts une lettre pr~c~dente [I]o Les impulsions ~lectriques excitant la vapeur ont une intensit~ de cr@te de l ' o r d r e de 250A. Le spectre a ~t~ explor~ dans une gamme de temperatures allant de 500oc (pression ~ 2.10-4 torr) ~ 850oc (pression 0°8 t o r r ) . L e t u b e l a s e r e s t e n a l u m i n e , d ' u n e l o n g u e u r de 1 m e t d ' u n d i a m ~ t r e de 5 ~t 10 mmo T o u t e s l e s r a i e s ont ~t~ o b s e r v ~ e s a v e c au m o i n s 2 d e s 4 g a z p o r t e u r s u t i l i s ~ s ( a r g o n , n~on, h ~ l i u m ou h y d r o g ~ n e ) , d o n t la p r e s s i o n e s t e n g 6 n ~ r a l n e t t e m e n t s u p ~ r i e u r e ~ c e l l e d e la v a p e u r m ~ t a l l i q u e : 1 ~ 3 m m s e l o n l a n a t u r e du g a z . L e s r 4 s u l t a t s o b t e n u s s o n t r ~ s u m ~ s d a n s le tableau ci-dessous. L'ensemble des transitions 150
int~ress4es couvre un domain spectral allant de iol ~ ~t 6.5 ~o La raie X = 1.50 /I est de beaucoup la plus intense° Elle a ~t~ pr~vue par W. To Walter et coll. [31. Ces auteurs ont ~nonc~, sous forme de 5 crit~res, les propri6t~s requises pour les niveaux entre lesquels est susceptible de s'~tablir une inversion de population dans une d~charge en impulsions° La raie X = 1.50 /i s a t i s f a r ~t ces 5 crit~res. A 760oc, 5 transitions peuvent ~tre obtenues en superradiance: X = 1.13 p, = 1.50 ~, k = 1¢90 ~, ~ = 2o15 ~ et X= 2.47 ~. A cette temperature, nous avons ~valu~ le gain ~t 65 dB/m pour ~ = 1°13 ~ et ~t 40 dB/m pour ~ = = 1.50/I. P a r m i les t a l e s non identifi~es, l'une d'elle (X = 6.45 ~) pourrait gtre attribu4e ~t la transition du strontium I: 5p IP 1 ~ 4d ID 2, En effet, la presence d'une tr~s faible quantit~ de cet ~l~ment dans le baryum pourrait expliquer l'oscillation de cette raie, pr~vue et observ4e avec une tr~s forte intensit~ par ailleurs [3,4 I.
FERROMAGNETIC
PHYSICS LETTERS
PROPERTIES
OF
Co-Ga
ALLOYS
29 June 1970
WITH
B2
STRUCTURE
Jo G. BOOTH and J. D. MARSHALL
Deparlrnenl of Pure and Applied Physics, Unieersily of SalfoJ'd, Salford 5, Lancs.. UK Received 22 May 1970
Cobalt-rich CoGa alloys having the ordered bcc (B2) structure are reported to be ferromagnetic. The magnetization and Curie temperatures are proportional to the square of the excess Co concentration.
R e c e n t m a g n e t i z a t i o n m e a s u r e m e n t s [1] on the o r d e r e d bcc (B2) a l l o y s of the CoAl s y s t e m have shown that the a l l o y s r i c h e r in cobalt than 50% a r e f e r r o - m a g n e t i c , f e r r o m a g n e t i s m being a s s o c i a t e d with the s u b s t i t u t i o n of cobalt a t o m s into the g a l l i u m lattice, producing defect or "antistructure ~ atoms. We r e p o r t h e r e m a g n e t i z a t i o n and s u s c e p t i b i l i t y m e a s u r e m e n t s on the r e l a t e d CoGa s y s t e m in which the B2 s t r u c t u r e is s t a b l e o v e r a w i d e r c o m p o s i t i o n r a n g e (44 to 66 % Co a p p r o x i m a t e l y ) . T h e s e a l l o y s have not p r e v i o u s l y been r e p o r t e d to be f e r r o m a g n e t i c . The m e a s u r e m e n t s w e r e made o v e r the t e m p e r a t u r e r an g e 4,2 to 300°K in f i e l d s up to 17 kOe using a v i b r a t i o n m a g n e t o m e t e r ( P r i n c e t o n App l i e d R e s e a r c h Corp) in which s p e c i m e n t e m p e r a t u r e s w e r e i n d i ca t e d by a c a l i b r a t e d c o p p e r constantan t h e r m o c o u p l e p l a c e d in c l o s e p r o x i m ity to the s a m p l e . The a l l o y s w e r e f a b r i c a t e d f r o m 4N8 cobalt r o d s and 5N g a l l i u m ingots by r e p e a t e d m e l t i n g in an a r g o n - a r c f u r n a c e . A f t e r m e l t i n g the a l l o y s w e r e c r u s h e d , s e a l e d in q u a r t z unde r vacuum, and a n n e a l e d at 830°C f o r 24 h o u r s with s u b s e q u e n t quenching into w a t e r . C h e m i c a l a n a l y s i s was p e r f o r m e d f o r cobalt content° X - r a y e x a m i n a t i o n showed only the p r e s e n c e of B2 l i n es and m e t a l l o g r a p h s did not r e v e a l the p r e s e n c e of a s e c o n d phase. A l l o y s r i c h e r in cobalt than 51% w e r e found to be f e r r o m a g n e t i c and C u r i e t e m p e r a t u r e s T c w e r e d e t e r m i n e d by plotting ~ 2 T a g a i n s t H/CrHT [2] to d e t e r m i n e the i s o t h e r m a l p ~ s s in g through the o ri g i n . It was noted that a l l o y s within 2 o r 3 p e r c e n t of the e q u i a t o m i c c o m p o s i t i o n w e r e u n s a t u r a t e d at 4.2 OK and 17 kOe. Fig° 1 shows p l o t s of ~T c and 4-(~o o (the i n s t r i n s i c m a g n e t i z a t i o n ) a g a i n s t cobalt c o n c e n t r a t i o n . A l i n e a r r e l a t i o n s h i p is e v i d e n t as was found f o r CoAl in [1], and the i n t e r c e p t at 50.7% Co is c l o s e to the c o m p o s i t i o n at which Co a t o m s e n t e r
•K½
,-J_,
..~ 52
54 56 Atomic Percent Cobolt
(¢rnu/glg
58
60
Fig. 1. Relationship between (a) ( T c and cobalt concentration and (b) ~/~oo and cobalt concentration for CoGa alloys. the Ga l a t t i c e [3]. The f e r r o m a g n e t i c p r o p e r t i e s can t h e r f o r e be a s s o c i a t e d with the f o r m a t i o n of cobalt a n t i s t r u c t u r e a t o m s in the g a l l i u m lattice. If we a s s u m e that only t h e s e a n t i s t r u c t u r e a t o m s have m a g n e t i c m o m e n t s a s s o c i a t e d with them in the CoGa B2 phase the r e s u l t s shown in table 1 c o l u m n s 5 and 6 a r e obtained. The m a g n e t i c m o m e n t p e r e x c e s s cobalt atom deduced f r o m the low t e m p e r a t u r e m a g n e t i z a t i o n m e a s u r e m e n t s ( f e r r o P x s Co ) and f r o m the slope of the inverse susceptibility versus temperature curve (para ~ x s Co ) a r e shown, The m o m e n t s obtained f r o m the f e r r o m a g n e t i c data a r e in a s i m i l a r r an g e to those o b s e r v e d f o r Co in CoAl a l l o y s [1]. Howe v e r those deduced f r o m the p a r a m a g n e t i c data a r e c o n s i d e r a b l y l a r g e r . Such a d i s p a r i t y m ay be o b s e r v e d f o r m a t e r i a l s which fall into the 149
Volume 32A. number
3
Saturation magnetization. netic moment per excess
At ~:,; Cobalt 52,5 53.9 54.4 56.6 58.2 60.6
Excess Ate,: Cobalt 1.8 3.2 3.7 5.3 7.5 9.9
PHYSICS
Table 1 Curie temperature, and magcobalt atom for CoGa alloys.
(~o o
Tc -I °K
e . m . u, g. 1.9 3.1 5.0 12.3 18.1 30,1
LETTERS
9 20 25 73 122 228
Para PXSCo (P'B) 1.2 1,1 I .5 2.7 2.8 3.5
Para PXSCo (~B) 7 6 6 6 6 8
29 June 1970
t i o n of t h e 59Co a n d 27A1 s i g n a l s f o r a Co50°5A149.5 a l l o y h a v e s u g g e s t e d t h a t s o m e l o c a l i z e d m o m e n t s e x i s t in t h a t a l l o y s y s t e m , a n d a l t h o u g h m e a s u r e m e n t s on Co r i c h a l l o y s h a v e not y e t b e e n m a d e i t i s p o s s i b l e t h a t s u c h a s i t u a t i o n o b t a i n s f o r the a l l o y s u n d e r d i s c u s s i o n here° References
c a t e g o r y of i n t i n e r a n t f e r r o m a g n e t s , e s p e c i a l l y if w e a k I41, but it s h o u l d b e m e n t i o n e d t h a t Van O s t e n b u r g e t al. [51 on t h e b a s i s of t h e o b s e r v a -
[1] S.R. Butler. J . E . H a n l o n a n d R . J . W a s i l e w s k i . J. Phys. Chem. Solids 30 (1969} 1929. [21 J . S . Kouvel and M . E . F i s h e r . Phys. Rev. 136A (1964) 1626. [31 K. Schubert. H,L. Lukas, H . - G . M e i s s n e r and S. Bhan, Z.Metallk. 50 (1959) 534. [41 E . P . Woh[farth. J. Appl. Phys.. 39 (1968) 1061. [5] D.O. Van Ostenburg. J . J . Spokas, C.H. Sowers and H.G. Hoeve. Phys. L e t t e r s 30A (1969) 130.
N O U V E L L E S R A I E S L A S E R I N F R A R O U G E S DANS LA V A P E U R DE B A R Y U M Ph. CAHUZAC Laboraloire
Airn~
Cotton
- C, N.R.S.
II -
91 O R S A Y - F r a n c e
Received 28 April 1970
New pulsed l a s e r actions have been obtained in barium vapor. Twenty infrared l a s e r lines have been observed in this vapor.
Dans la vapeur de baryun, nous avons observ~ en impulsions 20 nouvelles t a l e s l a s e r infrarougeso Cette ~tude fair suite ~t celle concernant les t e r r e s r a r e s [1,2]. La m~thode exp~rimentale utilis~e est celle d~j~t d4crite darts une lettre pr~c~dente [I]o Les impulsions ~lectriques excitant la vapeur ont une intensit~ de cr@te de l ' o r d r e de 250A. Le spectre a ~t~ explor~ dans une gamme de temperatures allant de 500oc (pression ~ 2.10-4 torr) ~ 850oc (pression 0°8 t o r r ) . L e t u b e l a s e r e s t e n a l u m i n e , d ' u n e l o n g u e u r de 1 m e t d ' u n d i a m ~ t r e de 5 ~t 10 mmo T o u t e s l e s r a i e s ont ~t~ o b s e r v ~ e s a v e c au m o i n s 2 d e s 4 g a z p o r t e u r s u t i l i s ~ s ( a r g o n , n~on, h ~ l i u m ou h y d r o g ~ n e ) , d o n t la p r e s s i o n e s t e n g 6 n ~ r a l n e t t e m e n t s u p ~ r i e u r e ~ c e l l e d e la v a p e u r m ~ t a l l i q u e : 1 ~ 3 m m s e l o n l a n a t u r e du g a z . L e s r 4 s u l t a t s o b t e n u s s o n t r ~ s u m ~ s d a n s le tableau ci-dessous. L'ensemble des transitions 150
int~ress4es couvre un domain spectral allant de iol ~ ~t 6.5 ~o La raie X = 1.50 /I est de beaucoup la plus intense° Elle a ~t~ pr~vue par W. To Walter et coll. [31. Ces auteurs ont ~nonc~, sous forme de 5 crit~res, les propri6t~s requises pour les niveaux entre lesquels est susceptible de s'~tablir une inversion de population dans une d~charge en impulsions° La raie X = 1.50 /i s a t i s f a r ~t ces 5 crit~res. A 760oc, 5 transitions peuvent ~tre obtenues en superradiance: X = 1.13 p, = 1.50 ~, k = 1¢90 ~, ~ = 2o15 ~ et X= 2.47 ~. A cette temperature, nous avons ~valu~ le gain ~t 65 dB/m pour ~ = 1°13 ~ et ~t 40 dB/m pour ~ = = 1.50/I. P a r m i les t a l e s non identifi~es, l'une d'elle (X = 6.45 ~) pourrait gtre attribu4e ~t la transition du strontium I: 5p IP 1 ~ 4d ID 2, En effet, la presence d'une tr~s faible quantit~ de cet ~l~ment dans le baryum pourrait expliquer l'oscillation de cette raie, pr~vue et observ4e avec une tr~s forte intensit~ par ailleurs [3,4 I.