Effects of Mechanical and Thermal Treatment on the Structure and Magnetic Transitions in FeRh

Abstract

Well‐annealed bulk samples of the intermetallic compound FeRh exhibit a first‐order transition from antiferromagnetic to ferromagnetic order on heating near 330°K. Plastic deformation has been found to convert the normal CsCl‐type ordered structure of FeRh to a disordered fcc structure, which is only weakly magnetic and does not exhibit the first‐order transition. On annealing the disordered material at T_a=510°K, three stages of effects have been observed. In the first, the fcc phase converts to a highly ordered CsCl‐type structure, the magnetization at T_a increasing with a time constant of ∼10 min; the material is strongly ferromagnetic down to low temperatures. In the second stage, there is a much slower (τ≈400 min) increase in magnetization at T_a with a gradual return of the first‐order transition at lower temperatures. In the third stage, there is no further increase in magnetization at T_a, but the first‐order transition continues to increase in completeness and sharpness. The slow return of the first‐order transition is attributed to the gradual attainment of perfect long‐range order or, alternatively, to the annealing out of defects produced by plastic deformation.