Temperature evolution of magnetic phases near the thickness-dependent metal-insulator transition in La$_{1-x}$Sr$_x$MnO$_3$ thin films observed by XMCD

TL;DR

This study investigates how magnetic phases in La$_{1-x}$Sr$_x$MnO$_3$ thin films evolve near the metal-insulator transition using temperature-dependent XMCD, revealing phase separation behavior at the nanoscale.

Contribution

It provides the first quantitative analysis of magnetic phase fractions in ultrathin LSMO films near the phase boundary using element-specific XMCD.

Findings

Identified coexistence of PM, SPM, and FM phases as temperature varies.

Quantified phase fractions using XMCD and microscopic modeling.

Supported phase separation as key to magnetic behavior in thin films.

Abstract

Perovskite-type manganites, which are well-known for their intriguing physical properties such as colossal magnetoresistance (CMR) and half metalicity, have been considered as candidate materials for spintronics. However, their ferromagnetic (FM) properties are often suppressed in thin films when the thickness is reduced down to several monolayers (MLs). In order to investigate how the magnetic phases evolve near the paramagnetic (PM)-to-FM phase transition boundary, we have performed temperature-dependent x-ray magnetic circular dichroism (XMCD) experiments on a La$_{1-x}$Sr$_{x}$MnO$_3$ (LSMO, $x=0.4$) thin film, whose thickness (8 ML) is close to the boundary between the FM-metallic and the PM-insulating phases. By utilizing the element-selectiveness of XMCD, we have quantitatively estimated the fractions of the PM and superparamagnetic (SPM) phases as well as the FM one as a function of temperature. The results can be reasonably described based on a microscopic phase-separation model.