Influence of Co-doping on the Crystal Structure, Magnetocaloric Properties and Elastic Moduli of the La(Fe, Si)₁₃ Compound

The La(Fe, Si)₁₃ compound shows a large magnetocaloric effect near room temperature. Partial substitution of Co for Fe can raise its Curie temperature and reduce the thermal hysteresis of its ferromagnetic transition. However, the influence of Co substitution on the crystal structure and magnetocaloric properties of La(Fe, Si)₁₃ is not well understood yet. In this work, we report a comparative study of the crystal structure, magnetocaloric effects and elastic moduli of polycrystalline LaFe_11.5Si_1.5 and LaCoFe_10.5Si_1.5 samples using synchrotron radiation X-ray diffraction, magnetic measurements and resonant ultrasound spectroscopy. Compared to the Co-free sample, the Co-doped sample shows a sluggish ferromagnetic transition and reduced volumetric expansion as well as softer elastic moduli at room temperature. The Co-doped sample also shows stronger temperature dependence of Fe-Fe distances in its ferromagnetic state. Such differences between the samples are explained by considering the influence of Co doping on ferromagnetic interactions and lattice entropy.