Interrelation between polycrystalline structure and time-dependent magnetic anisotropies in exchange-biased bilayers

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

“…Deposition rates have been η Cu = (6.7 ± 0.2) nm/min, η IrMn = (5.5±0.8) nm/min, η CoFe = (3.40±0.13) nm/min and η Si = (3.84 ± 0.96) nm/min for all layers, determined as described in Ref. [26]. Furthermore, an unbiased F sample with t F = 10 nm was fabricated as a reference by omitting the AF layer (t AF = 0 nm).…”

“…The base pressure was < 10 −6 mbar, the working pressure ≈ 10 −2 mbar and during deposition, an in-plane magnetic field set to 28 kA/m was applied. While the 20 nm Si capping layer serves as oxidation protection and further enhances the contrast in the magneto-optical measurements [28], the 5 nm Cu buffer layer induces the desired (111) texture in the IrMn layer [22,26].…”

“…The modification of the coercivity H C is attributed to rotatable AF moments resulting in a dynamic rotatable magnetic anisotropy (RMA) [18,19]. In polycrystalline systems, these anisotropies are -apart from to the AF/F-interface [20,21] and the AF crystal structure [22,23] -mainly determined by the grain volume distribution (GVD) of the AF [3,[24][25][26]. A general description of the EB in polycrystalline systems solidified over the last decades [3,8,25,27,28], connecting the AF GVD with the macroscopically observable features by subdividing the AF ensemble into classes of grains differently responding to rotating F magnetic moments during their reversal.…”

“…We present systematic thickness-dependent investigations of H EB and H C in the case of columnar grain growth, which we could validate by grain size analysis by means of atomic force microscopy. A quantitative connection between the averaged macroscopic magnetic characteristics and averaged microscopic material parameters is established by comparing thickness-dependent measurements with model calculations utilizing an extended time-dependent Stoner-Wohlfarth (SW) approach [26,28]. In conjunction, analytic expressions for the thickness-dependent relations were derived in the context of a generalized description of polycrystalline EB systems [3,25,28], which further solely depend on measurement conditions and parameters characterizing the averaged microscopic properties of the system.…”

Magnetic hysteresis of individual Janus particles with hemispherical exchange-biased caps

“…To model the effect of an exchange bias imposing a preferred direction on the magnetic moments in the ferromagnet, a unidirectional anisotropy is added to the simulation. Note that other influences of the afm layer are not accounted for, especially contributions to the coercive field 26 , rotational anisotropies 27 , or contributions arising due to its granular structure 28 . For this reason, neither the asymmetric values of the magnetic reversal fields nor the observed training effects are correctly reproduced by the simulation.…”