Physical properties of FeRh alloys: The antiferromagnetic to ferromagnetic transition

Abstract

The electronic, magnetic, thermodynamical, and transport properties of FeRh alloys are studied from first principles. We present a unified approach to the phase stability, an estimate of exchange interactions in various magnetic phases, and transport properties including the effect of temperature which are all based on the same electronic-structure model. Emphasis is put on the transition between the ferromagnetic (FM) and antiferromagnetic (AFM) phases. Such a study is motivated by a recent suggestion of FeRh as a room-temperature antiferromagnetic memory resistor. The theory predicts the order-disorder transformation from the hypothetical disordered bcc phase into ordered B2 phase. Comparison of exchange interactions in the magnetically ordered FM and AFM phases with corresponding spin-disordered counterparts allows us to identify relevant interactions which are precursors of magnetically ordered phases. The most important result is the explanation of a dramatic decrease of the resistivity accompanying the AFM to FM phase transition which is due to the spin disorder present in the system. The study of the anisotropic magnetoresistance in the AFM phase found recently experimentally is extended also to finite temperatures.

Magnetocaloric and barocaloric responses in magnetovolumic systems

“…4(c)] whereas points correspond to experimental data taken from different authors indicated in the inset. The fitting to the experimental data renders the following estimations zJ = 5.66 meV and = 36 (Å) 3 , comparable to recently reported values for the exchange constant [61] and the lattice parameter [53], respectively. The misfit between theory and experiments (∼10% around the tricritical point) is partially due to the more attention given in the fitting procedure at the behavior close to P = 0.…”

Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

“…The overall gain in energy is very small and it is impossible to clearly separate the competing contributions. But we may speculate that the strong hybridization of rhodium and iron states in both the AF and the FM phase, responsible for both the implicit splitting of Rh in the AF phase and the evolution of a net magnetic moment in the FM phase [51,52], is also decisive for the structural stability of B2 FeRh. This could explain why rather different mechanisms such as increasing the local exchange splitting of Fe via constrained magnetic moments, or decreasing the band width by increasing the volume, or shifting the relative position of the elemental orbitals using the GGA+U approach, have the same consequence, i. e., stabilizing the B2(AF) phase.…”

Modeling the thickness dependence of the magnetic phase transition temperature in thin FeRh films

“…There are a number of theoretical/computational models that can describe the ferromagnetic (FM) or antiferromagnetic (AFM) phase [25][26][27][28] and first-principles models can be used to understand the effects of interfaces and atomic termination [29]. The present approach allows for the simultaneous description of both the FM and the AFM phases using a single set of parameters, based on the atomistic spin dynamics formalism [30].…”