Magnetization depinning transition, anisotropic magnetoresistance and inplane anisotropy in two polytypes of La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ epitaxial films

TL;DR

This study investigates the magnetization depinning transition, anisotropic magnetoresistance, and in-plane anisotropy in two polytypes of La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ epitaxial films, revealing phase transitions and anisotropic resistance behaviors.

Contribution

It provides the first detailed analysis of magnetization pinning, depinning, and anisotropic magnetoresistance in these specific epitaxial film polytypes, including phase boundary mapping.

Findings

Magnetization is pinned along specific crystallographic directions in both polytypes.

A magnetization orientation phase transition occurs with hysteresis and discontinuity in resistance.

Resistance anisotropy follows R$_ot$ > R$_ ho$ across all fields and temperatures.

Abstract

The isothermal magnetoresistance [R($\theta$)] of [001] and [110] epitaxial films of La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ measured as a function of the angle $\theta$ between current ($\vec{I}$) and magnetic field ($\vec{H}$), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn - O - Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ($\vec{M}$) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in $R(\psi)$ where $\psi$ is the angle between $\vec{H}$ and the easy axis for the $\vec{H}$ below a critical value $\vec{H}^*$ has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R$_\bot$ and R$_\|$ for $\vec{I} \bot \vec{H}$ and $\vec{I} \| \vec{H}$, respectively for both polytypes follows the inequality R$_\bot >$ R$_\|$ for all ranges of fields ($0 \leq H \leq 3500Oe$) and temperatures (10K - 300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of D\"oring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.