Modulation of interfacial magnetic relaxation timeframes by partially uncoupled exchange bias

A set of partially uncoupled NiFe/Cu/IrMn exchange biased thin films with variable thickness of non-magnetic Cu spacer is characterized by ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) techniques applied complementary to reveal time-scale dependent effects of uncoupling between ferromagnetic and antiferromagnetic layers on high-frequency magnetization dynamics. The results correlate with interfacial grain texture variations and static magnetization behavior. Two types of crystalline phases with correlated microwave response are revealed at the ferro-antiferromagnet interface in NiFe/Cu/IrMn thin films. The first phase forms as well-textured NiFe/IrMn grains with NiFe (111)/IrMn (111) interface. The second phase consists of amorphous NiFe/IrMn grains. Intercalation of NiFe/IrMn by Cu clusters results in relaxation of tensile strains at the NiFe/IrMn interface leading to larger size of grains in both the NiFe and IrMn layers. The contributions of well-textured and amorphous grains to the high-frequency magnetization reversal behavior are distinguished by FMR and BLS techniques. Generation of a spin-wave mode is revealed in the well-textured phase, whereas microwave response of the amorphous phase is found to originate from magnetization rotation dominated by a rotatable magnetic anisotropy term. Under fixed FMR frequency, the increase of Cu thickness results in higher magnetization rotation frequencies in the amorphous grains.

Angle Magnetization Rotation Method for Characterizing Co-Rich Amorphous Ferromagnetic Microwires

A low-frequency model of the magnetization reversal of a microwire is developed for those cases when the microwire magnetization response can go beyond the linear approximation. The analysis of the influence of external magnetic fields on the process of magnetization reversal of the microwire, including the hysteresis mode, was performed. The characteristic dependences of the amplitude of the electromotive force, U2f, arising in the pick-up coil wound around the microwire are obtained. It was established that, in the region of relatively small-acting circular and longitudinal magnetic fields, the U2f signal could have a region with the opposite sign. An extended small-angle magnetization rotation method was used to verify the proposed model and test glass-coated, amorphous, Co-rich microwires. During the experiments, the amplitude of the second harmonic, U2f, arising in the pick-up coil when an alternating electric current with the frequency f flows through the microwire, was measured as a function of the applied longitudinal magnetic field at various mechanical tensile stresses. The effective anisotropy field, the magnetostriction constant, and the residual quenching stress of the investigated microwires were determined by comparing the theoretical and experimental data.

Magnetoelectric Coupling by Piezoelectric Tensor Design

Strain-coupled magnetoelectric (ME) phenomena in piezoelectric/ferromagnetic thin-film bilayers are a promising paradigm for sensors and information storage devices, where strain manipulates the magnetization of the ferromagnetic film. In-plane magnetization rotation with an electric field across the film thickness has been challenging due to the large reduction of in-plane piezoelectric strain by substrate clamping, and in two-terminal devices, the requirement of anisotropic in-plane strain. Here we show that these limitations can be overcome by designing the piezoelectric strain tensor using the boundary interaction between biased and unbiased piezoelectric. We fabricated 500 nm thick, (001) oriented [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (PMN-PT) unclamped piezoelectric membranes with ferromagnetic Ni overlayers. Guided by analytical and numerical continuum elastic calculations, we designed and fabricated two-terminal devices exhibiting electric field-driven Ni magnetization rotation. We develop a method that can apply designed strain patterns to many other materials systems to control properties such as superconductivity, band topology, conductivity, and optical response.

Stress Dependence of the Small Angle Magnetization Rotation Signal in Commercial Amorphous Ribbons

The results of the investigation on tensile stress dependence of the SAMR (small angle magnetization rotation) signal in soft magnetic amorphous ribbons are presented. Exemplary results for commercially available, negatively magnetostrictive 2705M, 2714A, and 6030D amorphous ribbons show significant stress dependence, in contrast to positively magnetostrictive 2826MB alloy. The magnetoelastic hysteresis of the obtained characteristics is compared, as well as the influence of the biasing H field and supply current variations. Based on the results, 2705M alloy with near-zero negative magnetostriction is proposed as best suited for a SAMR-based, magnetoelastic force sensor.

Coherent Magnetization Rotation of a Layered System Observed by Polarized Neutron Scattering under Grazing Incidence Geometry

The in-plane magnetic structure of a layered system composed of polycrystalline grains smaller than the ferromagnetic exchange length was studied to elucidate the mechanism controlling the magnetic properties considerably different from the bulk using polarized neutron scattering under grazing incidence geometry. The measured result, together with quantitative analysis based on the distorted wave Born approximation, showed that the in-plane length of the area with a uniform orientation of moments ranging from 0.5–1.1 μ m was not significantly varied during the process of demagnetization followed by remagnetization. The obtained behavior of moments is in good agreement with the two-dimensional random anisotropy model where coherent magnetization rotation is dominant.