Effect of Si substitution in ferromagnetic Pr2Fe17: a magnetocaloric material with zero thermal expansion operative at high temperature

Abstract

This article deals with the magnetic and thermal expansion properties of Pr₂Fe₁₆Si. This compound has been well characterized from the structural point of view by analysing X-ray diffraction (XRD) patterns. The temperature dependent behaviour of magnetization (M) and the structural parameters (lattice parameters, unit cell volume) suggest that the compound undergoes a second order phase transition from a paramagnetic to a ferromagnetic state at T_C = 390 K, driven by an increase in bond length between iron atoms at 6c sites. The field-dependent behaviour of M below T_C, and comparatively lower value of coercivity (H_c) have been explained by the role of Si atoms as pinning centres. In the ferromagnetic phase, the system is found to behave like an inhomogenous mean field system. The study of thermal expansion properties establishes that the compound is a zero thermal expansion material (α_v = 5.3 × 10⁻⁶ K⁻¹) operative in the temperature range T = 200–340 K. As a magnetocaloric material, Pr₂Fe₁₆Si possesses high RCP (87 J kg⁻¹ at μ₀H = 1.5 T), high operating temperature (390 K) and moderate |ΔS_M|^max.