Magnetic interaction in exchange-biased bilayers: a first-order reversal curve analysis

Abstract

The distributions of coercivities and magnetic interactions in a set of polycrystalline Ni0.8Fe0.2/FeMn bilayers have been determined using the first-order reversal curve (FORC) formalism. The thickness of the permalloy (Py) film was fixed at 10 nm (nominal), while that of the FeMn film varied within the range 0–20 nm. The FORC diagrams of each bilayer displayed two clearly distinguishable regions. The main region was generated by Py particles whose coercivities were enhanced in comparison with those in which the FeMn film was absent (sample O). The minor region was produced by Py particles with coercivities similar to or slightly higher than those of particles in the Py film of sample O. Each sample presented two distributions of interaction fields, one for each region, and both were centred slightly below the exchange-bias field, thus indicating a prevalence of magnetizing interactions. These results are consistent with a grain size distribution in the Py layer and the presence of uncompensated antiferromagnetic moments.

Polycrystalline exchange-biased bilayers: magnetically effective vs. structural antiferromagnetic grain volume distribution

“…One -to the knowledge of the authors -hitherto unanswered question is, whether the structural GVD is identical to the distribution of the magnetically active AF grain volumes. Therefore, a quantitative link between the magnetic characteristics of polycrystalline AF/F-bilayers and their microstructure is crucial, even if the connection between thickness-dependent relations of H EB and H C and the AF layer's granular characteristic, or the nature of the EB as an interface effect itself, can be reasoned [3,[29][30][31][32][33].…”

Propriedades magnéticas e supercondutoras de redes de nanofios de Ni acopladas a filmes de Nb

“…Tamanho de cristalito (nm) Nb (110) Nb (200) Nb (211) Nb (220) Ni (200) Ni (220) "A" 15, 9 ± 2, 0 10, 6 ± 1, 3 9, 0 ± 0, 5 8, 1 ± 0, 3 --"B"…”

“…O estudo e caracterização de sistemas magnéticos multiparticulados se ve altamente beneficiado pela utilização desta técnica, que tem a vantagem de proporcionar muita mais informação da que surge de considerar um simples ciclo de histerese [105]. A análise FORC tem sido aplicada a sistemas tão diversos como dots policristalinos sub-micrométricos de Co [106], multicamadas de Co/Pd [107], arranjos de nanopilares de Ni [108], ímãs nanoestruturados do tipo exchange-spring [109], e filmes heterogêneos com efeito de exchange-bias [110,111], entre outros. O desenvolvimento do método continua evoluindo a partir de estudos teóricos e experimentais [112], ainda mais, a técnica foi estendida a outras variáveis que apresentam histerese, como magnetorresistência em válvulas de spin [113,114], e histerese térmica em ligas de FeRh [115].…”