Exchange anisotropy in the nanostructured MnAl system

In this letter, we report on the achievement of exchange anisotropy magnitude in a nanostructured Mn55Al45 alloy fabricated by rapid solidification with large exchange bias values (H-E approximate to 13 kOe at 10K) and a blocking temperature of T-B similar to 95 K. Field-cooled magnetization loops show a prominent exchange bias for T < T-B signaling the simultaneous presence of antiferromagnetic and ferromagnetic phases at these temperatures. Structural probes confirm a majority presence of the high-temperature metastable hexagonal epsilon-MnAl in the as-solidified state with an intriguing double-Bragg peak structure indicative of phase separation. The observed exchange bias is hypothesized to originate from an intimate mixture of antiferromagnetic and nanoscaled ferromagnetic phases or dual mictomagnetic phases, approximating a cluster glass with well-defined variations in the local Mn concentration of the composition and leading to Mn-rich and Mn-poor regions with antiferromagnetic and ferromagnetic characters, respectively. (C) 2012 American Institute of Physics. [http://dx.org/10.1063/1.3695153]