Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb

TL;DR

This study uses point contact Andreev reflection to measure nanoscale spin polarization in (In,Mn)Sb, revealing persistent local magnetization above the Curie temperature and exploring interface effects.

Contribution

It provides new insights into nanoscale magnetic behavior and charge conversion at superconductor-ferromagnet interfaces in dilute magnetic semiconductors.

Findings

Local spin polarization persists above Curie temperature.

Surface transparency affects charge conversion models.

Nanoscale clusters maintain magnetization above phase transition.

Abstract

Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb are presented and analyzed in terms of current models of charge conversion at a superconductor-ferromagnet interface. We investigate the influence of surface transparency, and study the crossover from ballistic to diffusive transport regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample with Curie temperature Tc of 5.4 K allowed the determination of spin-polarization when the ferromagnetic phase transition temperature is crossed. We find a striking difference between the temperature dependence of the local spin polarization and of the macroscopic magnetization, and demonstrate that nanoscale clusters with magnetization close to the saturated value are present even well above the magnetic phase transition temperature.