Magnetic Yttrium Iron Garnet (YIG) nanoparticles (NPs) were prepared by sol–gel (SG) and solid-state (SS) reaction methods to elucidate the nanoscale size on the magnetic behavior of NPs. It is found that YIG prepared by these two methods are different in many ways. The average NP sizes prepared by SG and SS methods were calculated by Scherrer formula from XRD data. SEM images show the change in grain size for both types of NPs. The sintering temperature required to form pure garnet phase is 750°C for SG and 1000°C for SS NPs. The saturation magnetizations (Ms) were 1070 Oe for SG and 1125 Oe for SS NPs, respectively. The coercivity (Hc) of SS NPs are twice larger than SG NPs. This is due to the larger crystal sizes of the SS NPs, hence more crystal boundaries. Dynamic properties were studied by ferromagnetic resonance (FMR) technique in field-sweep and frequency-sweep mode at different fixed frequencies and at different fixed magnetic fields, respectively. Resonance field (Hr) observed to increase linearly with frequency both for SS and SG NPs. The stop-band bandwidth (frequency linewidth) is narrower for SG NPs in comparison to SS NPs. Microwave absorption property make this material as a strong candidate for microwave device applications.

Spintronic functionality in ferromagnetic materials is a next-generation technique, to be used in data storage, high-frequency communications, and logic devices with minimum energy consumption. Ultra-low energy consumption in high-speed logic devices can be envisioned by inducing ferromagnetic behavior into room temperature multiferroic materials. However, there is a scarcity of room temperature multiferroic materials which have a definite spin degree of freedom. To fully exploit these technological challenges, we introduce the induced ferromagnetism in bismuth ferrite (BiFeO ₃ , BFO) by doping transition metal (Cr, Ni, Co) elements. Our investigation initiates with the experimental study on chemically synthesized BiFe _{(1− x )} M _x O ₃ samples where x = 0.0625 (6.25%) and M = Cr, Ni and Co. Experimental findings are verified by theoretical simulation using density functional theory (DFT + U ) and gauge including projector augmented wave (GIPAW) based calculation. All the experimental studies are done at room temperature while the theoretical verification using DFT is carried to understand the underlying mechanism behind the magnetic behavior of doped BiFeO ₃ . It is done by optimizing the structural parameters comparable to the room temperature values. Microstructural and magnetic properties are studied using x-ray diffraction (XRD), transmission electron microscopy (TEM) and Vibrating sample magnetometer (VSM). All these experimental studies confirm the structural changes and induced ferromagnetism with doping. X-ray photoelectron spectroscopy (XPS) verified the reason behind this ferromagnetic property on the basis of oxygen vacancy content. Electron paramagnetic resonance (EPR) spectroscopy shows the tuning of Δg values due to enhanced magnetization. The density of states (DOS) calculations were performed on BFO (band-gap 1.89 eV) after structural optimization using DFT + U method, confirm our experimental findings. Magnetic moment values change drastically with doping elements (M), i.e. almost negligible for BFO (antiferromagnetic) to maximum (2.85 μ _B /f.u.) for Ni-doped sample. We also compute the EPR g -tensor using GIPAW method to confirm the tuning of Δ g values due to enhanced magnetization. These results can highlight the impact and importance of suitable transition element doping to induce the room temperature ferromagnetism in BiFeO ₃ .

Three-dimensional (3D) topological insulators (TIs) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet (FM) ${\mathrm{Fe}}_{78}{\mathrm{Ga}}_{13}{\mathrm{B}}_9$ (FeGaB) and 3D TI ${\mathrm{Bi}}_{85}{\mathrm{Sb}}_{15}$ (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. DC magnetization measurements establish the soft magnetic character of FeGaB films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing magnetization and large value of spin mixing conductance $(5.03\times {10}^{19}{\mathrm{m}}^{\text{–}2})$ as the spin angular momentum leaks into the TI layer. Magnetic field controlled bipolar DC voltage generated across the TI layer by inverse spin Hall effect is analyzed to extract the values of spin Hall angle and spin diffusion length of BiSb. The spin pumping parameters derived from the measurements of the femtosecond light-pulse-induced terahertz emission are consistent with the result of FMR. The Kubo-Bastin formula and tight-binding model calculations shed light on the thickness-dependent spin-Hall conductivity of the TI films, with predictions that are in remarkable agreement with the experimental data. Our results suggest that room temperature deposited amorphous and polycrystalline heterostructures provide a promising platform for creating novel spin orbit torque devices.

Yttrium Iron Garnet (YIG) and bismuth (Bi) substituted YIG (Bi_0.1Y_2.9Fe₅O₁₂, BYG) films are grown in-situ on single crystalline Gadolinium Gallium Garnet (GGG) substrates [with (100) and (111) orientations] using pulsed laser deposition (PLD) technique. As the orientation of the Bi-YIG film changes from (100) to (111), the lattice constant is enhanced from 12.384 Å to 12.401 Å due to orientation dependent distribution of Bi³⁺ ions at dodecahedral sites in the lattice cell. Atomic force microscopy (AFM) images show smooth film surfaces with roughness 0.308 nm in Bi-YIG (111). The change in substrate orientation leads to the modification of Gilbert damping which, in turn, gives rise to the enhancement of ferromagnetic resonance (FMR) line width. The best values of Gilbert damping are found to be (0.54 ± 0.06) × 10⁻⁴, for YIG (100) and (6.27 ± 0.33) × 10⁻⁴, for Bi-YIG (111) oriented films. Angle variation (ϕ) measurements of the H_r are also performed, that shows a four-fold symmetry for the resonance field in the (100) grown film. In addition, the value of effective magnetization (4πM_eff) and extrinsic linewidth (ΔH₀) are observed to be dependent on substrate orientation. Hence PLD growth can assist single-crystalline YIG and BYG films with a perfect interface that can be used for spintronics and related device applications.