Ferromagnetism in the Kondo lattice cerium nickel antimonide and cerium zinc(x) antimonide (x = 0.64, 0.66).

摘要

Ferromagnetic Kondo lattice systems CeNiSb3 and CeZn xSb2 (where x = 0.64, 0.66) have been studied with magnetic, thermal, transport properties. The additional experiments like magnetic field dependent physical properties and pressure dependent electrical resistivity measurements have been performed in order to widen the understanding on these compounds and also to study quantum criticality near ferromagnetic to non-magnetic/antiferromagnetic borders.; Extensive experiments (specific heat, resistivity, and pressure experiment) displayed in this thesis show that CeNiSb3(TC = 6K) is a ferromagnetic Kondo lattice system in local (or stable) magnet regime of the Doniach phase diagram with moderate Kondo energy scale. The localized f-moments form a helical array with ferromagnetic moment lying in the ac-plane and an antiferromagnetic component along the b-axis due to the spiral spin configuration. The polymorph beta-CeNiSb3, however, follows close to a simple ferromagnetic behavior with reduced energy gap. CeNiSb3 displays canonical Kondo lattice behavior like CeAl2 in antiferromagnetic case. Pressure experiment suggests the quantum critical point at around 60kbar. However, the electronic structure seems to be changed under pressure which causes two magnetic phases to coexist above 35kbar, displaying a complex phase diagram near the quantum critical point.; CeZnxSb2 orders ferromagnetically at 2.5K and 3.5K for x = 0.64 and 0.66 respectively. Although they are observed as good metals with small size of the Kondo effects and large crystal electric field gaps, they show unusual ferromagnetic behavior. Specific heat divided by temperature of CeZn.64Sb2 follows linearly in temperature with finite y-intercept of ∼ 80mJ/mol-K2. The resistivity, on the other hand, can be fit well with T2, indicating a simple ferromagnet/Fermi liquid in metallic system. Moreover, the fact that the gamma and T2 coefficient satisfies Kadowaki-Woods ratio suggests a dominant Fermi liquid contribution to the ferromagnetic spin-wave excitation to thermal and transport properties. TC increases in x = 0.66 probably due to the enhanced hybridization caused by increased carrier density. There emerges, however, another magnetic transition below 1K, which has anti ferromagnetic characteristic from the magnetic field dependent specific heat and resistivity experiment. Both transition temperatures increases as pressure increases, indicating small Kondo effect to the system.