Elastic Anomalies of the Half-metallic Itinerant Ferromagnet CoS₂ Associated with Magnetic Phase Transition

Abstract

Elastic properties of the half-metallic itinerant ferromagnet CoS 2 have been investigated by means of ultrasonic measurement. A pronounced precursor elastic anomaly towards T C was observed in the temperature dependence of elastic modes, probably associated with the ferromagnetic long-range order. The precursor elastic anomaly, however shifts to upper temperatures and becomes smeared upon increasing a magnetic field, in good agreement with the previously determined phase diagram of CoS 2. Results for the longitudinal elastic mode C L show a particular behavior at low temperatures. For further cooling, another slight elastic anomaly can be recognized around 100 K, far below T C. Data analysis of deformation potential approximation suggests that a coupling constant between a strain tensor and relevant quasiparticle bands with heavy masses near the Fermi level would be fairly large. We discuss the elastic property, and also the nature of the novel elastic anomaly observed in the magnetically ordered state of CoS 2 .