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The ubiquitous domain wall kinetics under magnetic field or current application describes the dynamic properties in nanostructured magnets. However, when the geometrical size of a nanomagnetic system is constricted to the limiting domain wall length scale, the competing energetics between anisotropy, exchange and dipolar interactions can cause emergent kinetics due to quasiparticle relaxation, similar to bulk magnets of atomic origin. Here, we present a joint experimental and theoretical study to support this argument -- constricted nanomagnets, made of antiferromagnetic and paramagnetic neodymium thin film with honeycomb motif, reveal fast kinetic events at ps time scales due to the relaxation of chiral vortex loop-shaped topological quasiparticles that persist to low temperature in the absence of any external stimuli. Such phenomena are typically found in macroscopic magnetic materials. Our discovery is especially important considering the fact that paramagnets or antiferromagnets have no net magnetization. Yet, the kinetics in neodymium nanostructures is quantitatively similar to that found in ferromagnetic counterparts and only varies with the thickness of the specimen. This suggests that a universal, topological quasiparticle mediated dynamical behavior can be prevalent in nanoscopic magnets, irrespective of the nature of underlying magnetic material., Comment: 26 pages, 11 figures (main text 9 pages, 4 figures; supplementary material 17 pages, 7 figures). arXiv admin note: text overlap with arXiv:2305.00093

Vortex magnetic structure in artificial honeycomb lattice provides a unique platform to explore emergent properties due to the additional Berry phase curvature imparted by chiral magnetization to circulating electrons via direct interaction. We argue that while the perpendicularly-aligned magnetic component leads to the quantized flux of monopole at the center of the Berry sphere, the in-plane vortex circulation of magnetization gives rise to unexpected non-trivial topological Berry phase due to the gauge field transformation. The unprecedented effect signifies the importance of vector potential in multiply-connected geometrical systems. Experimental confirmations to proposed hypotheses are obtained from Hall resistance measurements on permalloy honeycomb lattice. Investigation of the topological gauge transformation due to the in-plane chirality reveals anomalous quasi-oscillatory behavior in Hall resistance $R_{xy}$ as function of perpendicular field. The oscillatory nature of $R_{xy}$ is owed to the fluctuation in equilibrium current as a function of Fermi wave-vector $k_F$, envisaged under the proposed new formulation in this article. Our synergistic approach suggests that artificially tunable nanostructured material provides new vista to the exploration of topological phenomena of strong fundamental importance.

Envisaging antiferromagnetic spintronics pivots on two key criteria of high transition temperature and tuning of underlying magnetic order using straightforward application of magnetic field or electric current. Here, we show that NiSi metal can provide suitable new platform in this quest. First, our study unveils high temperature antiferromagnetism in single crystal NiSi with $T_{N} \geq 700$ K. Antiferromagnetic order in NiSi is accompanied by the non-centrosymmetric magnetic character with small ferromagnetic component in a-c plane. Second, we find that NiSi manifests distinct magnetic and electronic hysteresis responses to field applications due to the disparity in two moment directions. While magnetic hysteresis is characterized by one-step switching between ferromagnetic states of uncompensated moment, electronic behavior is ascribed to metamagnetic switching phenomena between non-collinear spin configurations. Importantly, the switching behaviors persist to high temperature. The properties underscore the importance of NiSi in the pursuit of antiferromagnetic spintronics., Comment: 8 pages, 6 figures

Magnetic semiconductors are at the core of recent spintronics research endeavors. Chemically doped II-VI diluted magnetic semiconductors, such as (Zn$_{1-x}$Cr$_{x}$)Te, provide promising platform in this quest. However, a detailed knowledge of the microscopic nature of magnetic ground state is necessary for any practical application. Here, we report on the synergistic study of (Zn$_{1-x}$Cr$_{x}$)Te single crystals using elastic neutron scattering measurements and density functional calculations. For the first time, our research unveils the intrinsic properties of ferromagnetic state in macroscopic specimen of (Zn$_{0.8}$Cr$_{0.2}$)Te. The ferromagnetism is onset at $T_c \sim$ 290 K and remains somewhat independent to modest change in the substitution coefficient x. We show that magnetic moments on Zn/Cr site develop ferromagnetic correlation in a-c plane with large ordered moment of $\mu$ = 3.08 $\mu_B$. Magnetic moment across the lattice is induced via the mediation of Te site, uncoupled to the number of dopant carriers as inferred from the density functional calculation. Additionally, the ab-initio calculations also reveal half-metallicity in x = 0.2 composition. These properties are highly desirable for future spintronic applications.