# Freestanding and flexible composites of magnetocaloric Gd$_5$(Si,Ge)$_4$ microparticles embedded in thermoplastic poly(methyl methacrylate) matrix

## TL;DR

This study develops flexible, freestanding composites by embedding magnetocaloric Gd$_5$(Si,Ge)$_4$ microparticles into a transparent PMMA matrix, enabling practical applications of brittle magnetic materials with maintained magnetocaloric properties.

## Contribution

It introduces a simple solvent casting method to create flexible composites with homogeneous microparticle distribution and analyzes their structural and magnetocaloric properties.

## Key findings

- Achieved near-homogeneous distribution of microparticles in PMMA.
- Observed a 2.5×10^3 ppm reduction in unit cell volume at 70 wt.% loading.
- Secondary phase effects on magnetocaloric response are reduced due to matrix interactions.

## Abstract

The implementation of processed magnetic materials onto thermoplastics can be an approach for practical application of brittle intermetallic materials with the advantage of enlarging the range of applications. In the present work, we evaluate the effect of blending magnetocaloric Gd$_5$Si$_{2.4}$Ge$_{1.6}$ micrometric particles with 3.4 $\mu$m in different weight fractions onto a flexible, transparent and non-magnetic poly(methyl methacrylate) (PMMA). A close to homogeneous grain distribution along the polymer surface were achiever by using a simple solvent casting method for evaluation of their magnetocaloric properties. From XRD analysis, it was found a relative unit cell volume reduction of $\sim$2.5$\times$10$^3$ ppm for the composite with 70 wt.\% of powder as a result of interfacial interactions between the components. Although PMMA does not influence the magnetic nature of microparticles main phase, a reduction on the amount of secondary monoclinic phase occurs for all produced composite samples. As a consequence, a weakening on the effect of secondary phases on the micropowder magnetocaloric response is observed as a result of hydrostatic pressure from the difference between thermal expansions of matrix and filler.