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HIGH PRESSURE STUDIES WITH THE
237Np(60)-RESONANCE : MAGNETIC PROPERTIES IN NpCo2Si2
J. Gal, J. Moser, G. Wortmann, C. de Novion, J. Spirlet, G. Kalvius
To cite this version:
J. Gal, J. Moser, G. Wortmann, C. de Novion, J. Spirlet, et al.. HIGH PRESSURE STUDIES WITH
THE 237Np(60)-RESONANCE : MAGNETIC PROPERTIES IN NpCo2Si2. Journal de Physique
Colloques, 1980, 41 (C1), pp.C1-129-C1-130. �10.1051/jphyscol:1980129�. �jpa-00219697�
JOURNAL DE PHYSIQUE Colloque C1, suppl&ment au no 1 , Tome 41, janvier 1980, page C1-129
HIGH PRESSURE STUDIES WITH THE 2 3 7 b ( 6 0 ) - R ~ ~ ~ ~ : MAGNETIC PROPERTIES
IN
NpCo2Si2+
XJ. Gal
,
J. Moser, G. Wortmann, C. de Novion,
J.C. spirletU and G.M. Kalvius Physik Department, Technische Universitat MUnchen, W. Germany.+
Nuclear Research Center, Negev, Israel.x CENFAR, B.P. 6 , Fontenay aux Roses, France.
r
l n s t i t u t Europe'en des Transuraniens, Karlsruhe, W . G e m y .High p r e s s u r e e x p e r i m e n t s on t h e a c t i n i d e s a r e e x p e c t e d t o r e v e a l i m p o r t a n t i n f o r m a - t i o n on t h e p r o p e r t i e s o r i g i n a t i n g from the 5 f - e l e c t r o n s . For some i n t e r m e t a l l i c nep- tunium compounds t h e l a t t i c e c o n s t a n t s and t h e Np-Np s e p a r a t i o n w e r e f o u n d t o s t r o n g l y i n f l u e n c e t h e m a g n e t i c c h a r a c t e r of t h e 5f- s h e l l ( l o c a l i z e d v e r s u s i t i n e r a n t moment / I / ) .
B e c a u s e o f t h e i r a - r a d i o a c t i v i t y a n d t o x i - t y , most of t h e a c t i n i d e s c a n be h a n d l e d o n l y i n s p e c i a l l y e q u i p p e d l a b o r a t o r i e s .
Fig. 1 : High pressure c e l l : 1 ,anvils; 2,8 support- ing rings; 3,binding rings; 4,teflon washers; 5, s t e e l cylinder; 6,backing block; 7,9,gasket; 10, aluminum container; 11,sample; 12,part of aluminum enclosure; 13,drive rod; 14,source; 15,r-rays
The b a s i c f e a t u r e s of t h e h i g h - p r e s s u r e t e c h n i q u e used i n o u r l a b o r a t o r y h a v e been o u t l i n e d e l s e w h e r e / 3 , 4 / . B e c a u s e o f t h e a - r a d i a t i o n o f 2 3 7 ~ p a d d i t i o n a l p r e c a u t i o n s
had t o be made. The h i g h - p r e s s u r e c e l l
i s
d i s p l a y e d i n F i g . 1 . The a c t i v e s a m p l e ( 1 1 ) i s e n c a p s u l a t e d i n a s m a l l aluminum c o n - t a i n e r ( 1 0 ) . T h i s was done i n t h e g - l a b o r a - t o r y , which p r o v i d e d t h e s a m p l e . The h i g h - p r e s s u r e c e l l d i f f e r s f r o m t h a t u s e d w i t h n o n - a c t i v e a b s o r b e r s / 3 , 4 / m a i n l y by an o u t e r s t e e l c y l i n d e r ( 5 ) , which s e a l s t h e i n n e r p a r t s o f t h e c e l l f r o m t h e o u t s i d e by two t e f l o n w a s h e r s ( 4 ) . The newly d e - s i g n e d g a s k e t ( 7 , 9 ) w i t h t h e s u p p o r t i n g r i n g s ( 2 , 8 ) , which p r e v e n t s a r a d i a l f l o w - i n g o f t h e p r e s s u r i z e d m a t e r i a l / 3 / , c o n - s i d e r a b l y r e d u c e s t h e r i s k of a b l o w - o u t . The l o c a t i o n o f t h e h i g h - p r e s s u r e c e l l i n - s i d e t h e h i g h - p r e s s u r e c l a m p i s i d e n t i c a l t o t h a t s h o w n . p r e v i o u s l y / 3 , 4 / . However, two a d d i t i o n a l s a f e t y p r e c a u t i o n s w e r e t a k e n : ( i ) D u r i n g t h e a p p l i c a t i o n of p r e s - s u r e , t h e clamp was p l a c e d i n s i d e a s e a l e d c o n t a i n e r and ( i i ) i n s i d e t h e c r y o s t a t , t h e clamp was a g a i n p r o t e c t e d by a c l o s e d a l u - minum c o n t a i n e r .VELOCITY (mmls 1
Fig.2: Velocity spectrum of NpCo2Si2 a t 35 kbar.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980129
C1-130 JOURNAL DE PHYSIQUE
35 kbar
:I-
100
80
I ) & I . I . I J
30 40 50 60 70 TEMPERATURE [K]
-
NpCo2 Si2
-
0 kbarFig.3: Thermal scan spectra
Tab.1: Hyperfine parameters and ordering tempera- tures o f NpCo2i2 a t various pressures (S i s given r e l a t i v e t o the 241Am(Az) source)
0 46.5(1.) 12.86(3) 273.6(5) 2.14(6)
5.5(5) 47.0(1.) 12.67(3) 272.7(4) 2.23(5) 17.0(1.) 47.5(1.) 12.21(2) 274.1(4) 2.14(3) 26.5(1.) 48.0(1.) 12.18(3) 273.9(5) 2.16(6) 35.0(: .) 50.0(t.) 11.93(3) 273.8(4) 2.20(5) U s i n g a 200mCi 2 4 1 ~ m ( ~ m ) s o u r c e , t w o d i f f e r - e n t k i n d s o f 2 3 7 ~ p ( 5 9 . 6 keV) MBssbauer e x - p e r i m e n t s w e r e p e r f o r m e d : ( i ) t h e h y p e r f i n e p a r a m e t e r s o f NpCo2Si2 a t v a r i o u s p r e s s u - r e s were o b t a i n e d b y t a k i n g v e l o c i t y s p e c - t r a a t c o n s t a n t t e m p e r a t u r e s b e t w e e n 4.2 K and 77 K ( s e e F i g . 2 ) . ( i i ) t h e p r e s s u r e de- pendence o f TN was d e t e r m i n e d b y means o f t h e " t h e r m a l s c a n " t e c h n i q u e , where t h e t r a n s m i s s i o n o f t h e 59.6 keV r a d i a t i o n t h r o u g h t h e a b s o r b e r was measured as a f u n c t i o n o f t e m p e r a t u r e w i t h t h e s o u r c e b e i n g moved a l t e r n a t e l y ' a t v=S and v=-S, w h e r e S i s t h e i s o m e r s h i f t ( s e e F i g . 3 ) . The r e l a t i v e change o f TN w i t h p r e s s u r e i s c l e a r l y v i s i b l e i n F i g . 3 . A l l d a t a o b t a i n -
e d i n NpCo2Si2 a r e c o m p i l e d i n T a b l e 1.
T h r e e p r o m i n e n t r e s u l t s can be e x t r a c t e d f r o m T a b l e 1: (i) t h e ( a n t i f e r r o m a g n e t i c /2/) o r d e r i n g t e m p e r a t u r e TN i n c r e a s e s w i t h a s l o p e o f dTN/dP=0.10(2) K / k b a r ; i n c o n - t r a s t t o t h i s , ( i i ) t h e h p y e r f i n e f i e l d B e f f r e m a i n s c o n s t a n t u n d e r p r e s s u r e and ( i i i ) S d e c r e a s e s 1 i n e a r l y w i t h p r e s s u r e : ( ~ S / J P ) ~ = - Z . ~ ( Z ) . l ~ - ~ r n m / s . k b a r , w h i c h means an i n c r e a s e o f s - e l e c t r o n d e n s i t y a t t h e 2 3 7 ~ p n u c l e u s w i t h p r e s s u r e . I n t e r m s of a model s u g g e s t i n g a l i n e a r p r o p o r t i o n a l i t y b e t w e e n t h e Np m a g n e t i c moment and B e f f / 5 / , o u r p r e s s u r e d a t a i n d i c a t e a c o n s t a n t
( a n d t h e r e f o r e r a t h e r l o c a l i z e d ) moment i n NpCo2Si2. T h i s c o n t r a s t s t h e b e h a v i o u r o f t h e c u b i c L a v e s phase compound NpOs2, which i s supposed t o be an i t i n e r a n t moment f e r r o m a g n e t / 5 / and w h e r e a d e c r e a s e o f B e f f and TC w i t h p r e s s u r e was r e c e n t l y ob- s e r v e d / 6 / . A d e t a i l e d d i s c u s s i o n o f t e t r a - g o n a l NpCo2Si2 needs a d d i t i o n a l p r e s s u r e s t u d i e s o f o t h e r i s o s t r u c t u r a l Np compounds as w e l l as a d e t e r m i n a t i o n o f t h e compres- s i b i l i t i e s .
R e f e r e n c e s
/I/ e.g. B.D. D u n l a p a n d G.M. K a l v i u s , i n : The A c t i n i d e s : E l e c t r o n i c S t r u c t u r e and R e l a t e d P r o p e r t i e s (ed. b y A.J.
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