Cyclic structural ordering induced by high energy ball milling in a Fe2.1Cr0.9Al magnetocaloric alloy

Current research on magnetocaloric materials (MCM) aims at developing low cost, environmentally friendly materials which can be manufactured by simple processes. We report the effect of high energy ball milling on the structural, magnetic and magnetocaloric properties of low cost Fe_2.1Cr_0.9Al alloys. The degree of structural order in the Fe-Cr sublattice was found to vary with milling time in a cyclic fashion at a milling speed of 600 rpm. This phenomenon was analyzed by a reaction rate model based on the stored energy during high energy milling. The sample possessed a B2 crystal structure before milling. Milling for 15 min. at 600 rpm induced structural changes to produce a L2₁ structure. Interestingly, the 15 min. milled sample exhibited ∼50% higher saturation magnetization (M_S) compared to the value before milling. The relative cooling power (RCP) also increased to 300 Jkg⁻¹ at 5 T, compared to a value of 244 Jkg⁻¹ before milling. Extended X-ray absorption fine structure (EXAFS) studies revealed the emergence of short range order in the milled samples.