Erase/restorable asymmetric magnetization reversal in polycrystalline ferromagnetic films

Abstract

Asymmetric hysteresis loops are generally found in exchange-coupled ferromagnetic/antiferromagnetic layers or composite. Once the film is deposited the magnetization reversal behaviour becomes certain due to the fixed anisotropy of the film. We report an asymmetric magnetization reversal, which is erase/restorable in polycrystalline soft magnetic film. When the film is pre-saturated at a high field in the induced uniaxial easy direction, the asymmetric hysteresis loops with one branch governed by "coherent rotation" and another branch with kink induced by mixed reversal mechanism of "coherent rotation" and "rotation/180 degrees-domain-wall-motion/rotation" are obtained. If the film is presaturated in the induced hard axis, the kink disappears and "normal" hysteresis behaviour is observed instead. Such asymmetric magnetization curve can be restored if the film is pre-saturated in the easy axis again. The observed phenomenon is originated from an embedded second magnetically hard phase which tunes the anisotropy in the film. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765652

Observation of complete inversion of the hysteresis loop in a bimodal magnetic thin film

“…1 from which it is clear that the NiFe film consists of a polycrystalline granular (10-30 nm) ferromagnetic (FM) phase with an average film composition of 45%Ni-55%Fe, along with a thin (1 to 2 nm) secondary Fe deficient phase at the grain boundaries [blue boundary region in Fig. 1(d 3 Fe nanograins is in the range of ∼20−80 Oe (previously reported) higher than the coercivity (measured H C = 0.5Oe) of the bulk Ni 45 Fe 55 alloy film [22][23][24][25]. Detailed magnetic measurements have been carried out in a superconducting quantum interference device (SQUID) magnetometer (MPMS XL5, Quantum Design) across a wide temperature range of 5-300 K under a maximum field H max of ±50 kOe .…”

“…When the external magnetic field is reversed the exchange bias coupling at the interface is developed at low fields due to the antiparallel alignment of nonreversed Ni 3 Fe with the reversed Ni 45 Fe 55 magnetization vector and spin pinning at the interface in the field reversal process. The volume fraction of Ni 3 Fe is extremely low (∼1.5%) and thus is expected to have an insignificant contribution to the film's total magnetization [21,25]. Hence, the descending part of the IHL is generated at the positive field quadrant due to the positive exchange bias coupling at the interface of two different magnetic phases, and negative remanence magnetization (−M R ) is obtained at a H = 0Oe field.…”