The magneuic study of rare-earth compounds CeRu2(Si1-xGex)2

• Main Authors: Feng, Shih-Weng, 馮世維
• Other Authors: C.Tien
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/17268305261308243139

碩士 === 國立成功大學 === 物理學系 === 86 === It is interesting to study rare-earth compounds containing Ce which oftenexhibit Kondo Effect 、RKKY Interaction and sometimes mixed valence 、Heavy Fermion Phenomena。For studying the properties in rare-earth compounds CeRu2(Si1-x Gex)2，we do the following experiments：X-ray powder diffraction、 susceptibility measurement、magnetization measurement、L3 X-ray absorption spectroscopy，specific heat measurement、and resistivity measurement。 The L3 X-ray absorption spectroscopy probes that the valence of CeRu2Si2 is3.03。 Therefore the 4f band is sufficiently close to but below the Fermi surface。From the small mixed-valence，we prove that when Kondo effect exists，the 4f electrons possess both localized and itinerant characters。CeRu2Si2 isone of the few cases of heavy- Fermion compound in which no evidence of long-range magnetic ordering has been found down to ~20mK。However CeRu2Ge2 orders ferromagnetically at 7.9K。The valence of CeRu2Ge2 is 3.000 so the 4f electron is well localized。 Both compounds have attracted considerable interests。Based on the twocompounds，we use alloying method to study the properties in the rare- earthcompounds CeRu2(Si1-xGex)2。CeRu2(Si1-xGex)2 can be considered a good exampleof studying competition between Kondo effect and RKKY Interaction。For x=、0.1， Kondo effect is stronger than RKKY Interaction so the long-rangemagnetic ordering fails to develop。For x = or >0.2，RKKY Interaction isstronger than Kondo effect so the magnetic ordering restores。 With increasingGe concentration，the antiferromagnetic order is depressed and the ferromagne-tic order is enhanced。In CeRu2Ge2 ，the antiferromagnetic transition disappearsand the ferromagnetic order is stronger。 In rare-earth compounds CeRu2(Si1-xGex)2，The correlation of magnetic moments on the same layer is ferromagnetic ordering。 The coupling between layer and layer is antiferromagnetic coupling。Replacing Si by Ge，the distancebetween layer and layer is larger。Thus the antiferromagnetic coupling betweenlayer and layer is decreased。 Therefore the ferromagnetic ordering is enhanced。