Magnetoresistances observed by decomposition of the magnetic moment in La1-xCaxMnO3 films

TL;DR

This study investigates the magnetic and electronic phases of La$_{1-x}$Ca$_{x}$MnO$_3$ thin films, revealing distinct high and low temperature magnetoresistance behaviors linked to ferromagnetic and semiconducting states.

Contribution

It demonstrates the effectiveness of the van der Pauw method in measuring magnetoresistance and uncovers the polaronic conduction and carrier density variations near the Curie temperature.

Findings

High-temperature CMR depends on magnetic moment

Low-temperature CMR is more sensitive to magnetic fields

Van der Pauw method outperforms four-probe in magnetic measurements

Abstract

A ferromagnetic phase, characterized by electron carriers and a high temperature colossal magnetoresistance (HTCMR) dependent on the magnetic moment, and a semiconducting phase, characterized by hole carriers and a low temperature CMR (LTCMR), are observed in La$_{1-x}$Ca$_{x}$MnO$_3$ thin films by the van der Pauw method. The LTCMR is much more sensitive to the magnetic field than the HTCMR. In the ferromagnetic phase for films with anisotropic moments in two dimensions, a remnant resistivity of the order of 10$^{-8} \~{\Omega}m$ is observed up to 100 K and increases exponentially with both a temperature up to $T_c$ and a magnetic field above one Tesla (a positive magnetoresistivity). We found that the ferromagnetic phase below $T_c$ is in a polaronic state with a polaronic mobile conduction, and the carrier density dips near $T_c$. For resistances measured by the four-probe method with line electrodes, low temperature information of the HTCMR is not revealed. The van der Pauw method is more effective for the resistance measurement of a magnetic material than the four-probe method.