臺灣博碩士論文加值系統

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。