Investigation of the magnetic-non-magnetic crossover region in the Kondo lattice system CeSi_x

Abstract

AbstraeL Measurements of resistivity, susceptibility and magnetization b r polycrystalline samples of the alloys CeSi, (1.6 6 z 6 2.W) in the temperature range Q-UX) K show that samples with t < 1.85 order fetromagnetically while t h o x with 1: > 1.90 do not. This correlates well with previous studies of these samples. However, samples with z = 1.70 and 1.75 show the presence of an anomalous second peak at a slightly higher temperature than the ferromagnetic ordering temperature. CeSi, with z = 1.90 show interesting resistive behaviour with characteristics of both magnetic and non-magnetic samples It exhibits a broad low lemperature peak, a Kondo minimum at higher temperatures and the onset of Feimi liquid behaviour below the maximum. The magnitude of the r w m temperature resistivity is substantially larger than that of the other members of the series, indirating that this sample is very close lo .the critical conanlration for the magneticnon-magnetic transition in this series. High temperature anomalies are seen in the resistivities of samples with 2: > 1.90: nonetheless, no magnetic correlation is observed.Negative magnetoresistance is obsewed for samples CeSil,ro and CeSil.go over all fields and temperatures investigated.

Low-density approach to the Kondo-lattice model

“…CeCu 6 (x = 0) is non-magnetic because of perfect Kondo screening, while for x > 0.1 the RKKY component dominates taking care for an antiferromagnetic ordering up to x = 1 (CeCu 5 Au) with increasing Neel-temperature T N for increasing x. J < 0 does not necessarily lead to antiferromagnetism. The compound CeSi x is ferromagnetic for 1.6 ≤ x ≤ 1.85 [26] with a strongly reduced magnetic moment. The Curie temperature of the ferromagnetic Kondo system (J < 0) CeN i x P t 1−x first increases in between x = 0 and x = 0.5 from 5.8K (x = 0) to about 8.6K (x = 0.5) in order to decrease then rapidly and disappearing eventually at x = 0.55 [27].…”

“…We want to construct an approximate expression for the electronic selfenergy of the low-density KLM, which fulfills the zero-bandwidth limit (26) for all temperatures T and arbitrary coupling strengths J, as well as the exact T = 0-result (27) and (28) for arbitrary bandwidths and couplings. Furthermore, it should reproduce the correct high-energy (strong coupling) behaviour (39) and in addition also the weak-coupling result (33).…”

Ferromagnetism within the Periodic Anderson Model: A New Approximation Scheme

“…Ferromagnetism is found in several Kondo lattice and HF materials. For instance, in CeSi x phase transitions as functions of the Si concentration were observed [2], or in the heavy fermion compound CeP d 2 Ga 3 , ferromagnetic ordering breaks down as function of external pressure [3]. For CeSi x , the magnetic phase diagram with † corresponding author: Dietrich.Meyer@physik.hu-berlin.de respect to the Si concentration x seems quite clear, but some effects accompaying the magnetic ordering, like the irregular resistivity behaviour, are not yet understood.…”