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 Ta=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 Ta 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 Ta with a gradual return of the first-order transition at lower temperatures. In the third stage, there is no further increase in magnetization at Ta, 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.