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.

Anomalous metamagnetic-like transition in a FeRh/Fe3Pt interface occurring at T ≈ 120 K in the field-cooled-cooling curves for low magnetic fields

“…4 However, the later can not explain the fact that the fch curve of the film stack evolves continuously as T increases above 100 K, with values lying well below the fcc curve (this up to temperatures near 220 K). As mentioned, the fcc and fch curves for pure Fe 3 Pt are much closer when compared to the large separation of the same curves in the film stack, evidencing the effect of the FeRh layer in the fch curve in the temperature region 100 K-220 K. The same effect seems to explain the reduction in the magnetisation of the zfc curve of the film stack relatively to the zfc curve of Fe 3 Pt (for Fe 3 Pt, the reduction in magnetization observed in the zfc curve below 230 K is a consequence of a misalignment of the domains, since as the temperature (or field) is increased the domains become more aligned). The zfc curve of the film stack, which lies well below the correspondent fch curve, also evolves continuously from 1.8 K up to 220 K. To better exemplify this discussion, it is plotted in the inset of Fig.…”

“…The low angle diffraction curve was obtained about one year after 18 the diffraction curve presented in the inset of Fig. 1 was obtained and, besides the Fe 3 Pt peaks, it also shows a signal due to Fe 3 O 4 , which is absent in the diffraction curve show in the inset figure. This fact evidences that Fe 3 O 4 grew in the FeRh surface of the film.…”

“…[1][2][3] In this cubic phase, equiatomic FeRh is antiferromagnetic and exhibits a metamagnetic magnetostructural phase transition at ambient temperature. The transition temperature is however highly sensitive to small changes out of the equiatomic stoichiometry 4 and microstructural scale.…”

“…The Fe 1−x Rh x with x ≈ 0.5 thin film was obtained by electrodeposition on a 0.6 cm 2 of a thick ordered Fe 3 ). The final film thickness of FeRh falls in the range of 30-50 nm, depending on the applied current density, which was varied from 1 to 5 mAcm −2 , and the charge for preparing all deposits was kept to 10 C. [14][15][16] An EG-G PAR potentiostat-galvanostat, model 273, served as a constant current source.…”

Stress Induced Phase Transition of Iron-Rhodium Alloys

“…[l] The transition to fcc structure was found rather earlier than the other stress-induced phase transition: It was first reported in 1960's by Lommel and Kouvel, who reported that fcc single phase powder was produced from B2 ordered FeRh alloys by filing at room temperature, and the same phase transition could be induced by cold rolling. [4] They observed the change in the magnetization of the stress induced fcc phase with temperature. The fcc phase was paramagnetic at room temperature, and metastable under 510K.…”