Magnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn$_x$Si$_{1-x}$ ($x\approx0.5$) alloy films

TL;DR

This study investigates the magnetic anisotropy of polycrystalline Mn$_x$Si$_{1-x}$ alloy films with varying manganese content, revealing complex anisotropic behavior linked to strain and structure, with high Curie temperatures near 300 K.

Contribution

It provides a detailed phenomenological analysis of magnetic anisotropy in polycrystalline MnSi films, highlighting the effects of strain and mosaic structure on magnetic properties.

Findings

High Curie temperature (~300 K) for x=0.52-0.55

Complex magnetic anisotropy with second and fourth order contributions

Inhomogeneous anisotropy due to strain at crystallite boundaries

Abstract

A set of thin film Mn$_x$Si$_{1-x}$ alloy samples with different manganese concentration x = 0.44 - 0.63 grown by the pulsed laser deposition (PLD) method onto the Al$_2$O$_3$(0001) substrate was investigated in the temperature range 4 - 300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies (f = 7 - 60 GHz) and magnetic fields (H = 0 - 30 kOe). For samples with x = 0.52 - 0.55, FMR data show clear evidence of ferromagnetism with high Curie temperatures T$_\text{C}$ ~ 300 K. These samples demonstrate complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second order easy plane anisotropy contribution and the additional forth order uniaxial anisotropy contribution with easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch. The existence of extra strains at the crystallite boundaries leads to an essential inhomogeneous magnetic anisotropy in the film plane.