High resolution photoemission on UPdSn and UNiA1

High-resolution UV photoelectron spectroscopy on heavy-fermion antiferromagnet UNiA1 displays a broad triangular 5f emission spread from E F dowIl to at least 1 eV. The presence of 5f states at EF, in contrast to the low T value of 5 mJ mol1 K-2, is observed also in local-moment antiferromagnet UPdSn. The considerable degree of itinerancy is demonstrated in both cases by 4f core-level spectra. 1. I n t r o d u c t i o n Varia t ions in the 5f e lec t ron local izat ion of ac t in ide in te rmeta l l i cs can lead to di f ferent t y p e s of g r o u n d state. P h o t o e l e c t r o n s p e c t r o s c o p y is in p r inc ip le a power fu l m e t h o d for fol lowing detai ls of the local iza t ion p r o c e s s on a m i c r o s c o p i c scale. However , it is no t ye t c lear the e x t e n t to which the p h o t o e m i s s i o n s p e c t r a a re a f fec ted by f inal-s tate effects in the case o f ma te r i a l s wi th s t rong e l e c t r o n e l e c t r o n cor re la t ions , or the ex t en t to which they ref lect the under ly ing s ingle-par t ic le e lec t ron ic s t ruc ture . The a i m o f the p r e s e n t inves t iga t ion is to con t r ibu te to the unde r s t and ing of the bas ic cha rac t e r i s t i c s o f the e lec t ron ic s t ruc tu re o f u r a n i u m in termeta l l ics . W e have c o n c e n t r a t e d on p h o t o e m i s s i o n s p e c t r o s c o p y s tudies on t e rna ry u r an ium c o m p o u n d s o f the t y p e UTX. Sys t ema t i c r e s e a r c h of the i r bulk p r o p e r t i e s has p rov ided a g o o d b a c k g r o u n d for s tudies us ing m i c r o s c o p i c me thods . Var ia t ion in the T and X c o m p o n e n t s p rov ides a wide s p e c t r u m of phys ica l behav iour . F o r an i n t r o d u c t o r y s tudy, two o f t hem, UNiA1 and UPdSn, w e r e se lec ted as repr e sen t a t i ves o f different c l a s ses o f c o m p o u n d s . UNiA1 is a n t i f e r r o m a g n e t i c be low TN= 19 K, bu t the s low m a g n e t i c sa tu ra t ion in fields a b o v e the m e t a m a g n e t i c t rans i t ion (Be = 11.3 T) and the low m a g n e t i c m o m e n t s ( abou t 0.6 ~B p e r u r a n i u m a t o m ) indica te an i t inerant c h a r a c t e r o f the m a g n e t i s m . Also the h igh T value o f 164 m J tool -1 K -2 indica tes the p r e s e n c e of i t inerant 0925-8388/92/$5.00 © 1992Elsevier Sequoia. All fights reserved