Magnetoresistance tensor of ${\text{La}}_{0.8}{\text{Sr}}_{0.2}{\text{MnO}}_3$

We measure the temperature dependence of the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in $c$-axis-oriented epitaxial thin films of ${\text{La}}_{0.8}{\text{Sr}}_{0.2}{\text{MnO}}_3$ for different current directions relative to the crystal axes, and show that both AMR and PHE depend strongly on current orientation. We determine a magnetoresistance tensor, extracted to fourth order, which reflects the crystal symmetry and provides a comprehensive description of the data. We extend the applicability of the extracted tensor by determining the biaxial magnetocrystalline anisotropy in our samples.

Figure 1

(Color online) $\rho$ vs $T$ with (solid circles) and without (empty circles) an applied magnetic field of $H=4\text{T}$. Inset: Sketch of the relative orientations of the current density $\mathbf{J}$, magnetization $\mathbf{M}$, and the crystallographic axes. ${\rho }_{\text{long}}$ is measured between $A$ and $B$, ${\rho }_{\text{trans}}$ is measured between $B$ and $C$.

Figure 2

(Color online) Longitudinal resistivity ${\rho }_{\text{long}}$ (left) and transverse resistivity ${\rho }_{\text{trans}}$ (right) vs $\alpha$, the angle between the magnetization and [100], for different angles $\theta$ (the angle between the current direction and [100]) at different temperatures with an applied magnetic field of 4 T). The solid lines are fits to Eqs. (5, 6).

Figure 3

(Color online) The ratios of the coefficients from Eqs. (5, 6) ($B/A$ and $C/A$) (left axis) and the coefficient $K_1$ from Eq. (9) (right axis) as a function of temperature.

Figure 4

(Color online) Left: PHE signal as a function of $\beta$, the magnetic field direction relative to the [100] ($H=500\text{Oe}$ and $T=50\text{K}$). The line is a fit to Eq. (6) with $\alpha$ extracted using Eq. (9). Right: PHE as a function of magnetic field. The sample is prepared with $\mathbf{M}$ along [100], and the field is applied along $\left[1\overline{1}0\right]$. The line is a fit using Eq. (9).