Anomalous Hall effect in the high-temperature ferrimagnetic semiconductorsBaFe2±xRu4∓xO11

Abstract

Field and temperature dependences of the magnetic and transport properties of single crystals of ${\text{BaFe}}_{2+x}{\text{Ru}}_{4\ensuremath{-}x}{\text{O}}_{11}$ $(x=0.5,0.9,1.4)$ R-type ferrites are reported. A wide homogeneity range of Ru/Fe compositions allows to tune the strength of the anomalous Hall effect (AHE), the width of the semiconducting gap $(\ensuremath{\Delta})$, and the temperature of magnetic ordering $({T}_{C})$ within one structural family. These parameters are enhanced for higher Fe content. A large Hall resistivity ${\ensuremath{\rho}}_{xy}=77\text{ }\ensuremath{\mu}\ensuremath{\Omega}\text{ }\text{cm}$ observed in single-crystal ${\text{BaFe}}_{3.4}{\text{Ru}}_{2.6}{\text{O}}_{11}$ at 300 K is several orders of magnitude large than that observed for bulk magnetic materials, and comparable to the Hall resistivity of thin films of magnetite. The anomalous Hall coefficient ${R}_{s}$ changes sign at a characteristic temperature ${T}^{\ensuremath{\ast}}$ that depends on the Fe/Ru ratio, which we attribute to variations in the electronic band structure. The ${R}_{s}$ vs longitudinal resistivity $({\ensuremath{\rho}}_{xx})$ dependence of ${\text{BaFe}}_{3.4}{\text{Ru}}_{2.6}{\text{O}}_{11}$ can be described in terms of negative skew and positive side-jump scattering contributions that differ above and below ${T}^{\ensuremath{\ast}}$. The very small side jump $\ensuremath{\Delta}y$ estimated from the contribution to the AHE that is quadratic in ${\ensuremath{\rho}}_{xx}$ suggests that the AHE is caused by a Karplus-Luttinger (Berry phase) mechanism.