Single domain magnetic nanoparticles (MNPs) have been a vivid subject of intense research for the last fifty years. Preparation of magnetic nanoparticles and nanostructures has been achieved by both bottom‐up and top‐down approaches. Single domain MNPs show Néel‐Brown‐like relaxation. The Stoner‐Wohlfarth model describes the angular dependence of the switching of the magnetization of a single domain particle in applied magnetic fields. By varying the spacing between the particles, the inter‐particle interactions can be tuned. This leads to various supermagnetic states such as superparamagnetism, superspin glass, and superferromagnetism. Recently, the study of the magnetization dynamics of such single domain MNPs has attracted particular attention, and observations of various collective spin wave modes in patterned nanomagnet arrays have opened new avenues for on‐chip microwave communications. MNPs have the potential for various other applications such as future recording media and in medicine. We will discuss the various aspects involved in the research on MNPs.

Antiferromagnetic materials (AFMs) have recently been attracting interest in research on spintronics due to their zero stray magnetic field, high anisotropy, and spin-orbit coupling. In this context, the bimetallic AFM ${\mathrm{Mn}}_2\mathrm{Au}$ has drawn attention because it exhibits unique properties and its Néel temperature is very high ($T_N=1500\mathrm{K}$). Here, we report investigations of spin pumping and the inverse spin Hall effect (ISHE) in a ${\mathrm{Mn}}_2\mathrm{Au}/\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$ bilayer system using ferromagnetic resonance. We find a large spin Hall angle ${\theta }_{\mathrm{SH}}=0.22$, with a spin Hall conductivity ${\sigma }_{\mathrm{SH}}=1.46\times {10}^5(\hslash /2e){\mathrm{\Omega }}^{-1}{\mathrm{m}}^{-1}$, comparable to that of $\mathrm{Pt}$. Further, we evaluate the effective spin-mixing conductance $g_{\mathrm{eff}}^{\uparrow \downarrow }=3.27\times {10}^{18}{\mathrm{m}}^{-2}$ and intrinsic spin-mixing conductance $g_r^{\uparrow \downarrow }=8.83\times {10}^{18}{\mathrm{m}}^{-2}$, which are higher than the previously reported value ($1.40\times {10}^{18}{\mathrm{m}}^{-2}$ for ${\mathrm{Mn}}_2\mathrm{Au}/{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$).

We have performed micromagnetic simulations to study the formation of skyrmions from an initial single bubble domain state in ferromagnetic elements with different shapes having perpendicular anisotropy. The strength of Dzyaloshinskii–Moriya interaction ( D ) and uniaxial anisotropy ( K ) are varied to elucidate the regime in which skyrmion formation can take place. It is found that for a certain combination of D and K , skyrmion formation does not happen. Further, we also observed that for large D and small K values, finite size effect dominates, which in turn hinders the formation of typical Néel (spherical) skyrmions. However, the resulting magnetic phase is skyrmionic in nature and has different shapes. We also have found that the shape of the magnetic nano element has a significant role in determining the final magnetic state in addition to the competing D and K values.

Probing the hybridized magnetic interface between organic semiconductor (OSC) and ferromagnetic (FM) layers has drawn significant attention in recent years because of their potential in spintronic applications. Recent studies demonstrate various aspects of organic spintronics such as magnetoresistance, induced interface moment etc. However, not much work has been performed to investigate the implications of such OSC/FM interfaces on the magnetization reversal and domain structure which are the utmost requirements for any applications. Here, we show that non-magnetic Fullerene can obtain non-negligible magnetic moment at the interface of Fe(15 nm)/C₆₀(40 nm) bilayer. This leads to substantial effect on both the magnetic domain structure as well as the magnetization reversal when compared to a single layer of Fe(15 nm). This is corroborated by the polarized neutron reflectivity (PNR) data which indicates presence of hybridization at the interface by the reduction of magnetic moment in Fe. Afterwards, upto 1.9 nm of C₆₀ near the interface exhibits magnetic moment. From the PNR measurements it was found that the magnetic C₆₀ layer prefers to be aligned anti-parallel with the Fe layer at the remanant state. The later observation has been confirmed by domain imaging via magneto-optic Kerr microscopy.

Noncollinear antiferromagnetic (AFM) materials have drawn research interest because they exhibit large anomalous Hall effect at room temperature (RT) due to large Berry curvature. ${\mathrm{Mn}}_3\mathrm{Ga}$ is a noncollinear AFM in which the order of Mn magnetic moments is arranged in inverse triangular configuration on a kagome lattice. It makes ${\mathrm{Mn}}_3\mathrm{Ga}$ a promising candidate for inverse spin Hall effect (ISHE) study which has not been studied before. In this work, investigation of ISHE and spin pumping in polycrystalline ${\mathrm{Mn}}_3\mathrm{Ga}$/CoFeB heterostructures at RT has been performed. Angle-dependent measurements of ISHE have been performed in order to disentangle various spin-rectification effects. Spin-mixing conductance ($g_{\mathrm{eff}}^{\uparrow \downarrow })$, spin Hall angle $\left({\theta }_{SH}\right)$, and spin Hall conductivity (${\sigma }_{SH}$) are evaluated to be $(5.0\pm 1.8)\times {10}^{18}{\mathrm{m}}^{-2}, 0.31\pm 0.01$, and $7.5\times {10}^5(\hslash /2e){\mathrm{\Omega }}^{-1}{\mathrm{m}}^{-1}$, respectively. The observed value of ${\theta }_{SH}$ is higher than ${\mathrm{Mn}}_3\mathrm{Sn}$ and comparable to the ${\mathrm{IrMn}}_3$, which is also a noncollinear AFM. Large spin Hall angle makes ${\mathrm{Mn}}_3\mathrm{Ga}$ a promising candidate for future spintronics devices.

We investigated the dependence of the seed (Ta/Pt, Ta/Au) and capping (Pt/Ta, Au/Ta) layers on the spin pumping effect in a 3 nm thick Co thin film using ferromagnetic resonance spectroscopy (FMR). The FMR data were fitted with Kittel’s equation to extract the values of the damping constant and g -factor. A strong dependence of the seed and capping layers on spin pumping has been discussed. The value of the damping constant ( α ) is found to be relatively large i.e. 0.0326 ± 0.0008 for the Ta(3)/Pt(3)/Co(3)/Pt(3)/Ta(3) (nm) multilayer structure, while it is 0.0104 ± 0.0003 for Ta(3)/Co(3)/Ta(3) (nm). An increase in α is observed, due to the Pt layer that works as a good sink for spins, due to high spin orbit coupling. In addition, we measured the effective spin conductance g ↓↑ = 5.82 ± 0.08 × 10 ¹⁸ m ⁻² for the structure Ta(3)/Pt(3)/Co(3)/Pt(3)/Ta(3) (nm) as a result of the enhancement in α relative to its bulk value. We observed that the evaluated g -factor decreases as effective demagnetizing magnetic field increases in all of the studied samples. The azimuthal dependence of the magnetic resonance field and line width showed relatively high anisotropy in the tri-layer Ta(3)/Co(3)/Ta(3) (nm) structure.