Theory of record thermopower near a finite temperature magnetic phase transition in IrMn

Abstract

The effect of scattering of conduction electrons by dynamical spin fluctuations on the thermopower in metals near a thermal phase transition into an antiferromagnetic phase is considered. We are interested in a transition at room temperature, as has been studied in a heterostructure involving layers of IrMn. We show that the electrical resistivity exhibits a narrow but low peak at the transition, which may be ddifficult to detect on top of the main contributions induced by phonons and impurities. By contrast, the thermopower is found to exhibit a prominent peak both as a function of temperature T for fixed layer thickness tAF M and as a function of tAF M for fixed T. We conjecture that the transition temperature Tc is a function of both tAF M and the Fermi energy F . Both dependencies give rise to a sharp peak of the thermopower as a function of T or tAF M near the transition. The estimated magnitude of the peak for the case of three-dimensional longitudinal spin fluctuations is in good agreement with experiment.

Large Thermopower Enhanced by Spin Entropy in Antiferromagnet EuMnSb2

“…Although the involved mechanism can be potentially more subtle, we propose that the simplest origin of the anisotropic coupling stems from the number of available itinerant electrons that are determined by the anisotropic gap closing effect under magnetic fields. [ 14 ] Finally, we mention that the scattering between charge carriers and dynamical spin fluctuations has been identified, both experimentally [ 38 ] and theoretically, [ 39 ] as an effective source for the boosted thermopower in antiferromagnets in the vicinity of T N . The role of such spin‐fluctuation‐related scattering in EuMnSb 2 deserves further explorations.…”

Observation of the Fluctuation Spin Hall Effect in a Low-Resistivity Antiferromagnet

“…Okamoto et al derived spin Hall conductivity σ SH sj and σ SH ss , which predict the nontrivial SHA enhancement around the ferromagnetic quantum critical point due to the critical spin fluctuations. For the AFM spin fluctuation, while the individual scattering processes scriptF 0,1 , scriptF 2 , and scriptF 3 (defined in ref and schematically shown in Figure a) remain the same as those in the ferromagnetic case, the microscopic mechanisms of the side-jump and skew-scattering contributions (Figure a) to the FSHE require further development (section IV of the Supporting Information). Schematically, the microscopic details of the two mechanisms consist of three scattering processes.…”