# Substrate Charge Transfer Induced Ferromagnetism in MnSe/SrTiO3 Ultrathin Films

## TL;DR

This paper explores how strain and charge transfer from a substrate can induce ferromagnetism and enhance conductivity in MnSe ultrathin films.

## Contribution

The study reveals that substrate-induced charge transfer leads to ferromagnetism and superparamagnetism in MnSe ultrathin films.

## Key findings

- Tetragonal MnSe ultrathin films show enhanced conductivity and superparamagnetism.
- Charge transfer from the SrTiO3 substrate increases unoccupied valence bands in MnSe.
- Optical absorption indicates enhanced electron transitions in tetragonal MnSe.

## Abstract

The observation of superconductivity in MnSe at 12 GPa motivated us to investigate whether superconductivity could be induced in MnSe at ambient conditions. A strain-induced structural change in the ultrathin film could be one route to the emergence of superconductivity. In this report, we present the physical property of MnSe ultrathin films, which become tetragonal (stretched ab-plane and shortened c-axis) on a (001) SrTiO3 (STO) substrate, prepared by the pulsed laser deposition (PLD) method. The physical properties of the tetragonal MnSe ultrathin films exhibit very different characteristics from those of the thick films and polycrystalline samples. The tetragonal MnSe films show substantial conductivity enhancement, which could be associated with the presence of superparamagnetism. The optical absorption data indicate that the electron transition through the indirect bandgap to the conduction band is significantly enhanced in tetragonal MnSe. Furthermore, the X-ray Mn L-edge absorption results also reveal an increase in unoccupied state valance bands. This theoretical study suggests that charge transfer from the substrate plays an important role in conductivity enhancement and the emergence of a ferromagnetic order that leads to superparamagnetism.