Strain Induced Anisotropic Magnetic Behaviour and Exchange Coupling Effect in Fe-SmCo$_{5}$ Permanent Magnets Generated by High Pressure Torsion

TL;DR

This study explores how high-pressure torsion induces nanostructure formation and modifies magnetic properties in Fe-SmCo$_{5}$ bulk magnets, revealing enhanced magnetization and coercivity linked to deformation-induced microstructural changes.

Contribution

It demonstrates the use of high-pressure torsion to produce bulk Fe-SmCo$_{5}$ nanocomposites with tunable magnetic properties through controlled deformation.

Findings

Increased saturation magnetization with higher strain.

Maximum coercive field at shear strain of 75.

Evidence of exchange coupling and phase decoupling at different temperatures.

Abstract

High-pressure torsion (HPT), a technique of severe plastic deformation (SPD), is shown as a promising processing method for exchange-spring magnetic materials in bulk form. Powder mixtures of Fe and SmCo$_{5}$ are consolidated and deformed by HPT exhibiting sample dimensions of several millimetres, being essential for bulky magnetic applications. The structural evolution during HPT deformation of Fe-SmCo$_{5}$ compounds at room- and elevated- temperatures of chemical compositions consisting of 87, 47, 24 and 10 wt.% Fe is studied and microstructurally analysed. Electron microscopy and synchrotron X-ray diffraction reveal a dual-phase nanostructured composite for the as-deformed samples with grain refinement after HPT deformation. SQUID magnetometry measurements show hysteresis curves of an exchange coupled nanocomposite at room temperature, while for low temperatures a decoupling of Fe and SmCo$_{5}$ is observed. Furthermore, exchange interactions between the hard- and soft-magnetic phase can explain a shift of the hysteresis curve. Strong emphasis is devoted to the correlation between the magnetic properties and the evolving nano-structure during HPT deformation, which is conducted for a 1:1 composition ratio of Fe to SmCo$_{5}$. SQUID magnetometry measurements show an increasing saturation magnetisation for increasing strain $\gamma$ and a maximum of the coercive field strength at a shear strain of $\gamma$ = 75.