Exchange anisotropy in the nanostructured MnAl system

Abstract

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 (HE ≈ 13 kOe at 10 K) and a blocking temperature of TB ∼ 95 K. Field-cooled magnetization loops show a prominent exchange bias for T < TB signaling the simultaneous presence of antiferromagnetic and ferromagnetic phases at these temperatures. Structural probes confirm a majority presence of the high-temperature metastable hexagonal ɛ-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.

Maximizing Exchange Bias in Co/CoO Core/Shell Nanoparticles by Lattice Matching between the Shell and the Embedding Matrix

“…1,2,4,5 In this respect, although archetypical exchange bias systems, e.g., AFM/FM bilayers or FM-AFM core/shell nanoparticles, typically exhibit HE values in the range of tens to hundreds of Oe; 1,2,4,5 HE values in excess of 10 kOe have also been occasionally reported. [14][15][16][17][18][19] However, apart from some possible minor-loop issues, 20,21 many of these systems are based on phase-separation. 14,16,17 This leads to illdefined FM and AFM counterparts often with FM phases of very small dimensions.…”

“…[14][15][16][17][18][19] However, apart from some possible minor-loop issues, 20,21 many of these systems are based on phase-separation. 14,16,17 This leads to illdefined FM and AFM counterparts often with FM phases of very small dimensions. Another strategy to obtain very large values for H E is using FM materials with very low magnetization.…”

Crystal structure, homogeneity range and electronic structure of rhombohedral γ-Mn5Al8

“…For temperature above 70 K, the straight line behavior in χ -1 (T) suggests that Mn 4.92 Al 8.08 (2) follows Curie-Weiss behavior with an estimated Curie-Weiss temperature of −190 K arrives from extrapolation of the linear portion of the χ -1 (T) curve. The corresponding effective moment of the Mn atom in the sample, as estimated from the relation μ eff =(8C/x) 1/2 with Curie constant C and molar fraction Mn x is 2.88μ B /Mn [57]. Below 70 K the susceptibility deviates from a simple Curie Weiss law and near 27 K manifests a broad feature with very clear zero-field-cooled and field-cooled hysteresis.…”

Appreciable Magnetic Moment and Energy Density in Single-Step Normal Route Synthesized MnBi

“…This is due to the fragile supply chain, responsible for providing adequate amounts of rare earth materials, making rare earth based magnets rare and expensive [5]. In this regard Mn-based inter-metallic materials such as MnBi [6] and MnAl [7] are attracting a lot of attention of materials scientist around the globe. These compounds also show good magneto-optical properties and hence could be used as permanent magnetic materials for new thermal writing media [8][9].…”