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The effect of the saturation field on the magnetization reversal of FePt(L10)/FeCo/CoO/FeCo multilayer (ML) has been investigated to understand the origin of asymmetric magnetization reversal and its correlation with exchange bias (EB). In the ML structure, the bottom FeCo layer is coupled to the hard FePt(L10) layer, and the top FeCo layer is comparatively free due to the relatively more distance from it. The ML has been deposited under UHV conditions and characterized at each stage of growth using magneto-optical Kerr effect and x-ray reflectivity techniques. Magnetization reversal is further studied through domain imaging using the Kerr microscopy technique. The experimental findings reveal that ML exhibits asymmetrical magnetization reversal for a certain range of azimuthal angles for both 1.5kOe and 50kOe saturation fields; however, this angular range of asymmetry decreases with the increase in the saturation field. Furthermore, EB was absent at the low saturation field, whereas, EB, in addition to asymmetry, is observed at the large saturation field. The origin of asymmetry is attributed to non-collinearity between magnetic anisotropy axes of both FeCo layers. It results from the proximity effect through short-range Heisenberg exchange interaction via the CoO barrier layer. On the other hand, EB arises due to unidirectional anisotropy induced in the FePt layer due to the high saturation field. It is further proposed that asymmetry would disappear when unidirectional anisotropy is strong enough to align both the FeCo layers in the saturation direction leading to loss of the non-collinearity between them., Comment: 16 pages, 8 figures, 1 table

Magnetoelastic and magnetoelectric coupling in the artificial multiferroic heterostructures facilitate valuable features for device applications such as magnetic field sensors and electric write magnetic-read memory devices. In a ferromagnetic/ferroelectric heterostructures, the strain mediated coupling exploits piezoelectricity/electrostriction in ferroelectric phase and magnetostriction/piezomagnetism in ferromagnetic phase. Such verity of these combined effect can be manipulated by an external perturbation, such as electric field, temperature or magnetic field. Here, we demonstrate the remote-controlled tunability of these effects under the visible, coherent and polarized light. The combined surface and bulk magnetic study of domain-correlated Ni/BaTiO3 heterostructure reveals that the system is strong sensitive about the light illumination via the combined effect of converse piezoelectric, magnetoelastic coupling and converse magnetostriction. Well-defined ferroelastic domain structure is fully transferred from a tetragonal ferroelectric to magnetostrictive layer via interface strain transfer during the film growth. The visible light illumination is used to manipulate the original ferromagnetic microstructure by the light-induced domain wall motion in ferroelectric, consequently the domain wall motion in the ferromagnetic layer. Our findings mimic the attractive remote-controlled ferroelectric random-access memory write and magnetic random-access memory read application scenarios, hence, can be proven as a novel perspective for room temperature device applications., Comment: 35 pages, 7 figures

We report the structural and magnetic properties of four-layer Aurivillius compound Bi$_5$FeTi$_3$O$_{15}$ (BFTO) at high hydrostatic pressure conditions. The high-pressure XRD data does not explicitly show structural phase transitions with hydrostatic pressure, however the observed changes in lattice parameters indicate structural modifications at different pressure values. In the initial pressure region values, the lattice parameters $\textit{a}$- and $\textit{b}$- are nearly equal implying a quasi-tetragonal structure, however as the pressure increases $\textit{a}$- and $\textit{b}$- diverges apart and exhibits complete orthorhombic phase at pressure values of about $\geq$8 GPa. Principal component analysis of high pressure Raman measurements point out an evident change in the local structure at about 5.5 GPa indicating that the evolution of the local structure under applied pressure seems to not follow crystallographic changes (long range order). Nuclear forward scattering (NFS) measurement reveal the development of magnetic ordering in BFTO at 5K with high pressures. A progressive increase in magnetic order is observed with increase in pressure at 5K. Further, NFS measurements carried out at constant pressure (6.4GPa) and different temperatures indicate that the developed magnetism disappears at higher temperatures (20K). It is attempted to explain these observations in terms of the observed structural parameter variation with pressure., Comment: 8 pages, 5 figures