Band metamagnetism and related phenomena in Er(Co1−xSix)2

Abstract

We report on magnetic, transport, and cohesive properties of Er(Co1−xSix)2 compounds in varying external conditions (T,H,p). The localized Er 4f magnetic moments in ErCo2 order ferromagnetically below TC=33 K. The Co 3d band states form no moment above TC, but below TC the majority and minority 3d sub-bands split due to strong 4f−3d exchange interaction. Consequently, Co moments of ∼1 μB appear coupled antiparallel to the Er moments. This is accompanied by a ∼50% resistivity drop and an abrupt lattice expansion. The sharp magnetization, resistivity, and volume anomalies in the critical temperature region indicate a first order magnetic phase transition. Detailed comparative studies reveal that the onset of Co magnetizm appears at T0∼(TC−1) K. Si substitution for Co enhances both, TC (up to 66 K for x=0.1) and ΔT=TC−T0, but the lattice parameter remains unchanged. In opposite, both the magnetovolume and resistivity anomaly at T0 become reduced. Pressure effect on TC(T0) is large and negative, ∂ ln TC/∂p∼−28 Mbar−1 for all x⩽0.1. Also the resistivity drop at T0 and the magnetovolume effect (ωs=3 ΔL/L=4.2×10−3 in ErCo2) below T0 become reduced with increasing pressure. The latter is reflecting reduction of the Co moment gained below T0.