Tuning exchange anisotropy in nanocomposite AgMn alloys

Abstract

Silver manganese alloys of composition Ag100−xMnx (25 ≤ x ≤ 40) were prepared by rapid solidification to investigate their reported antiferromagnetic character. Thorough characterization of their structural, compositional, and magnetic features indicates the formation of a phase-separated fcc-type structure in all studied alloys with lattice parameters and coherently diffracting region sizes on the order of 40–100 nm that are strongly correlated with the Mn content. Magnetic measurement reveals a blocking temperature TB ∼ 105 K that is accompanied by unprecedented exchange bias values up to 1.7 T (17 kOe) at low temperatures. The magnitudes of the exchange bias field and the blocking temperature increase with increasing Mn concentration, suggesting a very sensitive balance between Mn content and magnetic character in these alloys that fosters tuning of the resultant exchange bias.

Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

“…Areas that are more concentrated in Mn contain a greater number of Mn-Mn nearest-neighbor pairs with AF character, while regions of lower Mn content contain more Mn-Mn next-nearest-neighbor pairs, with ferromagnetic character [36,37]. Strong interactions between these two regions lead to large exchange bias (H ex ) values at T < T peak , analogous to the reported mictomagnetic character of AgMn or CuMn alloys in which compositional fluctuations and strong coupling between Mn-rich and Mn-poor areas yield the formation of exchange-biased loops [36,38]. Employing the assumptions of an atomic radius for Al of ~1.25 Å and ~1.40 Å for Mn [39], and utilizing the calculated unit cell volumes of the ε 1 and ε 2 phases in the alloy (Section 3) obtained by X-ray diffraction, it is determined that the Mn-rich phase contains ~64 ± 3 at.% Mn, whereas the Mn-poor phase contains ~60 ± 3 at.% Mn, within the Mn content range for the ε-phase proposed by Liu et al [40].…”

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.…”

Effects of coexisting spin disorder and antiferromagnetism on the magnetic behavior of nanostructured (Fe79Mn21)1−xCux alloys

“…10 The exchange anisotropy in Mn-containing alloys has been attributed to the coexistence of AFM and FM interactions due to inhomogeneous distribution of magnetic atoms, or to the intrinsic spinglass behavior in the case of diluted alloys. 3,8 To provide a better understanding of the magnetism displayed by Mn-based alloys, more investigations are needed on these complex systems when coexisting magnetic phases and/or spin disordered are present.…”

“…3 Among AFM systems that present exchange anisotropy when coexisting with other magnetic phases are metal transition oxide nanoparticles, [4][5][6] nanocrystalline FeRh alloy 7 and Mn-based alloys and compounds. 3,8 Within a core-shell description, mainly used to describe oxide nanoparticle systems, the surface shell behaves as a spin disordered system with spin-glass-like (SG-like) features that couples with the uncompensated AFM core giving rise to the EB phenomenon. [4][5][6]9 On the other side, mechanical milling applied to metallic systems produces nanostructured alloys 7 with ordered regions interconnected by disordered ones.…”