Magnetic study of FeSi_1−xGe_xacross the nonmagnetic-ferromagnetic transition

Abstract

Abstract. Magnetic properties of FeSi1−xGex have been investigated using polycrystalline samples. A transition from nonmagnetic state with an energy gap for x = 0 to a weak ferromagnetic state for x = 0.5 has been confirmed, which was previously reported by Yeo et al. using single crystalline samples. Pauli-paramagnetic contribution to the low temperature susceptibility, χspin(0), has been estimated for the samples with x ≤ 0.3 by fitting the observed data. It significantly increases with the increase of x, reaching the value χspin(0) = 0.75×10 −3 emu/mol, which is comparable to those of the nearly ferromagnetic metals YCo2 and Pd. Using the Arrot plot, the parameter F1 of the spin-fluctuation theory has been estimated. F1 shows a drastic decrease from the order of 10 6 K for x = 0 to 9.5×10 3 K for x = 0.5, which is very similar to the x dependence of F1 in Y(Co1−xAlx)2 across the nonmagnetic-ferromagnetic phase boundary. These results suggest that the evolution of the magnetism in FeSi1−xGex can be well understood in terms of the transition from nearly ferromagnetic to weak itinerant ferromagnetic metal.

Thermoelectricity in correlated narrow-gap semiconductors

“…Interestingly, spin excitations are moving notably quicker towards gapless behaviour with x than charge excitations, reminiscent of the above discussion on the non-equivalence of charge and spin gaps. Concomitantly, a Pauli-paramagnetic contribution appears in the magnetic susceptibility [195]. At low temperatures, the introduction of Ge drives a first order transition from a non-magnetic semiconductor to a ferromagnetic metal at x = 0.25.…”