Tuning the magnetostructural phase transition in FeRh nanocomposites

Effects of nanostructuring on the magnetostructural response of the near-equiatomic FeRh phase were investigated in nanocomposite materials synthesized by rapid solidification and subsequent annealing of an alloy of nominal atomic composition (FeRh)(5)Cu-95. Transmission electron microscopy studies confirm attainment of a phase-separated system of nanoscaled (similar to 10-15 nm diameter) precipitates, consistent with FeRh embedded in a Cu matrix. These nanoprecipitates are crystallographically aligned with the coarse-grained Cu matrix and possess an L1(0)-type (CuAu 1) structure, in contrast to the B2 (CsCl)-type structure of bulk FeRh. It is proposed that the face-centered cubic crystal structure of the Cu matrix serves as a template for the formation and stabilization of the L1(0) structure in the FeRh nanoprecipitates. Magnetic measurements highlight the existence of multiple magnetic phases in the material exhibiting spin-glass (T <= 15 K), ferromagnetic and paramagnetic (T > 20 K) behavior. A thermally hysteretic magnetic transition, remarkably similar to the magnetostructural transition of bulk CsCl-type FeRh reported at T-t = 370 K, is observed in the nanostructured material at 130 K. This result not only emphasizes the sensitivity of the magnetic and structural properties of FeRh to changes in microstructural scale, but also highlights the potential for tailoring magnetostructural transitions in functional materials systems via nanostructuring. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774282]