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

Abstract

The consequences of keV light-ion bombardment of polycrystalline exchange bias layer systems on individual magnetic anisotropies composing the effective unidirectional magnetic anisotropy are investigated by vectorial magneto-optic Kerr effect measurements. Preferential reduction of rotatable magnetic anisotropy as compared to the other magnetic anisotropies is observable, disproving the intuitive assumption of an equable weakening of all magnetic anisotropies due to the bombardment. It is concluded that light-ion bombardment has a stronger impact on the magnetic characteristics of smaller grains in a polycrystalline antiferromagnet as compared to those of larger ones.

Size limits of magnetic-domain engineering in continuous in-plane exchange-bias prototype films

“…The second and considerably weaker effect is the nuclear energy transfer causing defects in the atomic lattice structure [35]. These defects do not change the orientation of the local unidirectional anisotropy, but rather influence the local magnetic properties, as already explained in [35,40].…”

“…3). Since the theoretically predicted DW tails, calculated from [31] with the modification of the saturation magnetization [35] and the uniaxial magnetic anisotropy constant [40] are D tail,B = 1.32 μm for the bombarded and D tail,NB = 1.04 μm for the non-bombarded regions (see Appendix for details), it is evident that for b ≤ 2 μm there is a significant crosstalk between neighboring DWs. However, the smallest distinguishable periodic magnetic patterns are observable in Fig.…”

“…Micromagnetic simulations were carried out using the object-oriented micromagnetic framework (OOMMF) for a 10 nm thick Co 70 Fe 30 film assuming a uniaxial magnetic anisotropy constant of K F,NB = 4.5 × 10 4 J·m −3 for the non-bombarded areas [43] and K F,B = 0.71 K F,NB for the bombarded areas [40]. The saturation magnetization in the non-bombarded areas was chosen to be M s,NB = 1226 kA·m −1 and M s,B = 1175 kA·m −1 for the ion-bombarded regions [35].…”

Tailoring Perpendicular Exchange Bias Coupling in Au/Co/NiO Systems by Ion Bombardment

“…The FIB experiments clearly show that H EB can be enhanced by ion bombardment. This can be explained by the existing model for in-plane anisotropy polycrystalline layer systems [ 10 , 29 , 30 ]. Briefly, a two-energy-level model [ 29 ] can be applied to describe the coupling for a single domain AFM grain in contact with the FM layer.…”

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. Applied3010View full textAdd to dashboardCite

“…For high fluences, the decrease in n set could be more drastic and may outweigh the effect of decreasing AFM anisotropy constant, so interfacial defects may become important. It has recently been estimated that kiloelectronvolt He + IB of polycrystalline Ir-Mn/Co 70 Fe 30 films has a stronger impact on the magnetic characteristics of smaller interface grains with UCSs as compared to those of larger ones, reducing their rotatable anisotropy [44].…”