Evidence for vortex state in Fe2CoGe thin films using FORC and magnetic imaging

We report on the evidence for the vortex state in the thin films of Fe2CoGe through first order reversal curves, magnetic force microscope, longitudinal magneto-optical Kerr effect and micro-magnetic simulations. Phase purity of the films confirmed through X-ray diffraction, which confirms the A2 type disorder Heusler alloy structure. Contour graph of first order reversal curves infers the formation of vortex state that is useful to understand magnetization reversal and switching process. We do observe the vortex state ∼1 μm with in – plane curling of the magnetization using magnetic force microscope phase analysis. We believe that realization of vortex state formation in Fe2CoGe thin films may cater applications in future magnetic data storage and microwave oscillators

Spin transfer torque bias (STTB) due to domain wall resistance in an infinitely long ferromagnetic nanowire

The shift of a magnetization loop along the magnetic field axis for a ferromagnetic (FM)/anti-ferromagnetic (AFM) system when it is cooled through Néel temperature of AFM layer is called exchange anisotropy or exchange bias. Here, using micromagnetic simulations we propose that spin transfer torque (STT) mechanism would indeed be helpful in realizing the shift of the magnetization loop along magnetic field axis through domain wall (DW) resistance for an infinitely long FM nanowire without having AFM layer, which we call as spin transfer torque bias (STTB). Essentially, STTB is realized on both positive and negative magnetic field axes by varying the angle between spin polarized current and Zeeman field from 0 to 180 respectively and the origin is attributed to helical motion of the DW. However, we do not see STTB at 90 due to coherent rotation of domain. We also ascertain that STTB is also a function of magnetic anisotropy, current density, polarization strength and non-adiabatic STT term. Variation in STTB for different FM systems such as Fe2CoSi, Ni80Fe20 and Fe is attributed to a change in DW width. We believe that present results would lead to a new dimension in the field of spintronics. © 2021 IOP Publishing Ltd

Thickness-Dependent Magnetostatic Interactions and Domain State Configuration in Fe2CoSi Thin Films–FORC Analysis

We report on results pertinent to the room temperature first-order reversal curve (FORC) analysis of inverse Heusler alloy Fe2CoSi thin films with different thicknesses ( $t = 5$ , 10, 15, and 20 nm). Our analysis infers that magnetostatic interactions between magnetic grains enhance with an increase in the thickness of Fe2CoSi thin films. Indeed, such results are confirmed with the analysis of switching field distribution (SFD). Single domain (SD) to multi domain (MD) transformation is evidenced as the thickness increases from 5 to 20 nm. SD state is confirmed by symmetric contour around $B_{u} = 0$ axis, while, multidomain state is affirmed with no central peak and spreading of contour parallel to $B_{u} = 0$ axis. The change in domain state configuration for different thicknesses might strengthen the application of Fe2CoSi Heusler alloy films for the future spintronic applications. © 1965-2012 IEEE

Thickness dependent domain wall dynamics in Fe2CoSi thin films

We report on the effect of thickness on the magnetic properties and domain wall motion in as deposited Fe2CoSi thin films. Reflections present in selected area electron diffraction (SAED) micrograph infer that they are allowed reflections and are related to the Fe2CoSi. The coercivity is found to increase with the film thickness and the same is explained on the basis of Néel domain wall model. Longitudinal magneto-optical Kerr effect (L – MOKE) infers that the formation of ripple kind of domains that depend on the orientation of the field. L – MOKE data also infers nearly perfect 4-fold anisotropy for the film with thickness 5 nm and a weaker 4-fold anisotropy at higher thicknesses. Up on varying the angle between magnetic field and the film edge to 0° or 90°, indeed there is a transformation of the film magnetization from easy direction to hard direction. Fast Fourier transform of magnetic force microscopy (MFM) and polar plots infer a uniaxial anisotropy and a four-fold anisotropy in the films. Micromagnetic simulations infer that the coercivity value depends on the void size and enhances up to certain radius, above which it decreases. Present results would indeed be helpful for the future spintronic applications. © 2020 Elsevier B.V

Anomalous domain wall dynamics in Ir50Mn50/Fe2CoSi bilayers

We report on the evidenced anomalous saw-tooth and curved domains in the Si/SiO2/IrMn/Fe2CoSi/Ta bilayers. The existence of saw-tooth domains is attributed to higher magnetic charge density at the domain boundary induced by the IrMn layer, while curved domains are apparent due to Dzyaloshinskii-Morya interaction (DMI). On the other hand, straight domain walls are apparent as a result of uni–axial anisotropy and four-fold anisotropy along the easy axis. The curvature for the domain walls decreases upon changing the angle between sample edge and the magnetic field. We believe that the present results would indeed be helpful for the development of the domain wall motion devices. © 2022 Elsevier B.V