Structure and magnetic properties of Co2(Cr1−xFex)Al, (0 ≤ x ≤ 1) Heusler alloys prepared by mechanical alloying

Abstract

In the present study, a series of nanocrystalline Co2(Cr1−xFex)Al Heusler alloy powders were successfully prepared by high energy ball milling and the effect of substitution of Fe for Cr on the microstructure and magnetic properties was investigated in detail. The Co2CrAl alloy powder consisted of only A2 type disordered structure whereas the substitution of Cr by Fe led to the appearance of increasing amounts of B2 type disordered structure along with A2 type structure. All the Co2(Cr1−xFex)Al Heusler alloy powders demonstrated high spontaneous magnetization together with a very small hysteresis losses. The saturation magnetization, remanence, coercivity, and Curie temperature increased with increasing Fe content. The increasing magnetization with increasing Fe content was attributed to the replacement of antiferromagnetic Cr by strongly ferromagnetic Fe and an increasing amounts of relatively more ordered, atomically as well as ferromagnetically, B2 structure as compared to that of A2 phase. The increment in remanence and coercivity with increasing Fe content were associated with the variation in microstructural characteristics, such as grain size, lattice defects, and the presence of small amounts of magnetic/nonmagnetic secondary phases. The increment in Curie temperature with increasing Fe content was attributed to the enhancement of d-d exchange interaction due to the possible occupancy of vacant sites by Fe atoms. All the Heusler alloys indicated extremely low magnetic anisotropy and the relative anisotropy decreased with increasing Fe content.