Seebeck coefficient of Cr100−zOsz alloy system

Abstract

The magnetic phase diagram of the Cr100−zOsz alloy system exhibits possible quantum critical behavior (QCB), with commensurate spin-density-wave to paramagnetic (CSDW-PM) phase line terminating at z ≈ 14, in a superconducting dome at z ≈ 12. Also indicated is the co-existence of SDW antiferromagnetism (AFM) and superconductivity (SC) for the z = 12.2 sample with a bcc structure. Considering the unique behaviour in the Cr100−zOsz system, this study reports on an investigation into the temperature dependence of the thermoelectric power or Seebeck coefficient, ST. With S(T) sensitive to the electronic structure and scattering mechanisms it is used here in order to investigate the unique magnetic behaviour observed in this alloy. ST measurements were performed on polycrystalline Cr100−zOsz (2.1 ≤ z ≤ 14.1) samples, as confirmed by XRD to be in a single bcc phase. The low-temperature S(T) behaviour is expressed in the form S = aT + bT3, where a and b are constants that were determined to discuss the possible contributions of phonon and/or magnon drag to S. Resulting a(z) and b(z) behaviour indicate anomalies that can be associated with three crucial points in the Cr100−zOsz magnetic phase diagram: (i) at z ≈ 8 is associated with the destabilization of the CSDW phase with the continual addition of Os into the system, (ii) at z ≈ 12 where the SC properties manifest and (iii) at z ≈ 13 associated with quantum critical behaviour this the system. Considering dS/dT where T approaches 0 K, as function of z, clear anomalies are observed at z ≈ 12 and 13, which, are associated with the onset of SC and QCB in this system. The present results suggest that S is a decisive experimental parameter in characterizing anomalous behaviour reflected in the magnetic phase diagram of Cr100−zOsz.