The Hall effect and thermoelectric power correlated with the giant magnetoresistance in modified FeRh compounds

Abstract

Simultaneous measurements of the magnetoresistance, magnetization, Hall effect, thermoelectric power and specific heat of a modified FeRh compound where 3.5 at.% Ni is doped at the Fe sites are investigated in order to elucidate the origin of the giant-magnetoresistance phenomena through the metamagnetic transition from the antiferromagnetic (AF) to the ferromagnetic (F) state. The Hall coefficient changes its sign through the metamagnetic transitions. The sign of the thermoelectric power also changes from positive to negative through the transition from the AF to the F state. The electronic specific heat coefficient increases remarkably through the metamagnetic transition from the AF to the F state. These results imply that the giant-magnetoresistance effect in FeRh compounds results from the reconstruction of the Fermi surface across the metamagnetic transition. At low temperatures, two-step metamagnetic transitions were found, suggesting an uncompensated AF or ferrimagnetic state in the intermediate-field region around 2-3 T, only in the process of increasing the field.

Temperature-dependent transport properties of FeRh

“…Suzuki et al [9] suggest that, for deposited thin FeRh films, the main mechanism stems from the spin-dependent scattering of conducting electrons on localized magnetic moments associated with partially occupied electronic dstates [10] at grain boundaries. Kobayashi et al [11] have also discussed the MR effect in the bulk ordered FeRh system attributing its origin to the modification of the Fermi surface across the metamagnetic transition. So far only one theoretical investigation of the MR effect in FeRh has been carried out on an ab-initio level [12].…”

“…In this case the GMR effect can be attributed to the spin dependent scattering of conduction electrons which leads to a dependence of the resistivities on the relative orientation of magnetic layers, parallel or antiparallel, assuming the electronic structure of non-magnetic spacer to be unchanged. These arguments, however, cannot be straightforwardly applied to CsCl-structured FeRh, even though it can be pictured as a layered system with one atom thick layers, since the electronic structure of FeRh shows strong modifications across the AFM-FM transition as discussed, for example, by Kobayashi et al [11] to explain the large MR effect in FeRh. We use the calculated density of states at the Fermi level as a measure of the concentration of the conducting electrons.…”

“…In Fig. 4(a) we show our calculations of the total anomalous Hall resistivity for FeRh in the FM state, represented by the off-diagonal term ρ xy of the resistivity tensor and compare it with experimental data [11]. As the FM state is unstable in pure FeRh at low temperatures, the measurements were performed for (Fe 0.965 Ni 0.035 )Rh, for which the FM state has been stabilized by Ni doping.…”

Finite-temperature magnetism of FeRh compounds

“…Transport measurements demonstrate a strong drop of the electrical resistivity during the metamagnetic phase transition [16,22] from the AFM to the FM state. As the metamagnetic transition can be manipulated by an external magnetic field, this feature of the resistivity leads to a giant magnetoresistance phenomena in the system around T m , that makes FeRh an appealing material for future data storage devices [13,23].…”

Magnetothermodynamic Properties and Anomalous Magnetic Phase Transition in FeRh Nanowires

“…In this section, S in the patterned wire is characterized through electrical transport measurements. Four-terminal resistance measurement was performed on a 270 nm wide wire with sweeping temperature or in-plane 3 magnetic field as shown in Fig. 2.…”