Antiparallel interface coupling evidenced by negative rotatable anisotropy in IrMn/NiFe bilayers

Abstract

Negative rotatable anisotropy is estimated via ferromagnetic resonance measurements in as-made, annealed, and ion-irradiated IrMn 3 /Ni 81 Fe 19 bilayers. Opposite to previous observations, inverse correlation between rotatable anisotropy and coercivity is observed. The exchange-bias field, determined from hysteresis loop measurements, is higher than that obtained from ferromagnetic resonance for all samples. The results are discussed in terms of majority antiparallel coupling and magnetic-field-induced transitions from antiparallel to parallel states of uncompensated spins at ferromagnet/antiferromagnet interface. We affirm that an observation of negative rotatable anisotropy evidences antiparallel coupling even in systems presenting conventional exchange bias. V C 2015 AIP Publishing LLC. [http://dx

Exchange-bias and magnetic anisotropy fields in core–shell ferrite nanoparticles

“…The above-mentioned theoretical schemes, whatever useful, do not reflect in full the diversity of experimentally observed effects of the EB origin. In particular, comparative analysis of the quasistatic and magnetodynamic (ferromagnetic resonance) measurements points out that in CS particles, as in multilayer films, the exchange coupling, along with customary EB anisotropy, causes another type of anisotropy 22 , 23 . The latter is known as rotatable anisotropy (RA) 24 , and is unambiguously detected in ferromagnetic resonance (FMR) experiments where it manifests itself as an additional internal field that readily follows the direction of the imposed magnetizing field .…”

Preferential weakening of rotational magnetic anisotropy by keV-He ion bombardment in polycrystalline exchange bias layer systems

“…The two classes of layer systems most commonly used for modification by keV light-ion bombardment are polycrystalline Co/noble metal multilayers with an effective perpendicular-to-plane magnetic anisotropy and polycrystalline exchange bias layer systems with an effective in-plane magnetic anisotropy. Evidently the effective magnetic anisotropies in these layer systems result from a complex interplay of different individual magnetic anisotropies originating from interactions between layers or from the layers themselves [22][23][24][25][26]. Due to hyperthermal energy transfer from the ions into the layer system, implantation of ions, and defect creation the different prevailing magnetic anisotropies will be modified resulting in an altered effective magnetic anisotropy of the complete system.…”

“…One exception is the increase of the exchange bias field in polycrystalline exchange bias layer systems, which may be also explained by a decrease of magnetic anisotropy in larger antiferromagnetic crystallites [22,[27][28][29]. Although experimental evidence for the modification of the individual magnetic anisotropies via keV light-ion bombardment exists [26], a quantitative disentanglement of the individual contributions, allowing a corresponding experimental proof of such a conjecture, is still missing.…”

Unveiling the Mechanisms Governing the Exchange Coupling and Coercivity Modifications in Annealed or Ion-Irradiated Ir−Mn / Fe / Salazar1, Pereira2, Grande3 et al. 2018Phys. Rev. AppliedSelf Cite3010View full textAdd to dashboardCite

“…It is now accepted that the UCSs can be divided into four categories [8][9][10][11]: (i) Superparamagnetic UCSs, which are thermally unstable during the measurement and do not contribute to either H EB or coercivity (H C ) (i.e., half width of the hysteresis loop). (ii) Partially stable UCSs, which may rotate together with the FM's magnetization, resulting in H C enhancement and rotatable anisotropy [12][13][14][15]. (iii) Set UCSs (i.e., the ones preferentially aligned along H present during the preparation or post-treatment of the sample), which are responsible for the bias.…”