Large Current Driven Domain Wall Mobility and Gate Tuning of Coercivity in Ferrimagnetic Mn4N Thin Films

Current-driven fast magnetic octupole domain-wall motion in noncollinear antiferromagnets

Antiferromagnets (AFMs) have the natural advantages of terahertz spin dynamics and negligible stray fields, thus appealing for use in domain-wall applications. However, their insensitive magneto-electric responses make controlling them in domain-wall devices challenging. Recent research on noncollinear chiral AFMs Mn3X (X = Sn, Ge) enabled us to detect and manipulate their magnetic octupole domain states. Here, we demonstrate a current-driven fast magnetic octupole domain-wall (MODW) motion in Mn3X. The magneto-optical Kerr observation reveals the Néel-like MODW of Mn3Ge can be accelerated up to 750 m s-1 with a current density of only 7.56 × 1010 A m-2 without external magnetic fields. The MODWs show extremely high mobility with a small critical current density. We theoretically extend the spin-torque phenomenology for domain-wall dynamics from collinear to noncollinear magnetic systems. Our study opens a new route for antiferromagnetic domain-wall-based applications.

Measurement of the Dzyaloshinskii-Moriya Interaction in Mn4N Films That Host Skyrmions

Mn₄N thin film is one of the potential magnetic mediums for spintronic devices due to its ferrimagnetism with low magnetization, large perpendicular magnetic anisotropy (PMA), thermal stability, and large domain wall velocity. Recent experiments confirmed the existence of tunable magnetic skyrmions in MgO/Mn₄N/Cu_xPt_1-x(x = 0, 0.5, 0.9, 0.95), and density functional theory (DFT) calculation provided a large theoretical value of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) of Mn₄N/Pt, which is consistent with the predicted chemical trend of the DMI in transition metal/Pt films. So far, the measured DMI has not been reported in Mn₄N, which is needed in order to support the predicted large DMI value. This paper reports the average DMI of MgO/Mn₄N(17 nm)/Cu_xPt_1-x(3 nm) extracted from the anomalous Hall effect with various tilted angles, which is based on magnetic droplet theory with DMI effects. The DMI decreases from 0.267 mJ/m² to 0.011 mJ/m² with non-linear tendencies as Cu concentration in the Cu_xPt_1-x capping layer increases from 0 to 1, demonstrating the control of the DMI through the Cu_xPt_1-x capping layer. Furthermore, a solid solution model is developed based on an X-ray photoelectron spectroscopy (XPS) compositional depth profile to analyze the possible effects on the DMI from the mixing layers at the surface of Mn₄N. After taking into account the mixing layers, the large DMI in Mn₄N film with Pt capping is consistent with the predicted DMI.

Magnetization Compensation Temperature and Frustration-Induced Topological Defects in Ferrimagnetic Antiperovskite Mn_{4}N

First-principles-based simulations are conducted to investigate magnetic properties and topological spin textures in the antiperovskite Mn_{4}N ferrimagnet. A magnetization compensation temperature, resulting from a competition between different Mn sublattices, is found in this system, when under thermal equilibrium. Striking metastable topological states are also discovered, including nanometric hedgehog-antihedgehog pairs that originate from frustrated exchange interactions rather than the usual Dzyaloshinskii-Moriya interaction.

Microstructure, magnetic and electronic transport properties of reactively facing-target sputtered epitaxial Mn4N films

The structure, magnetic and electronic transport properties of epitaxial Mn₄N films fabricated by the facing-target reactive sputtering method have been investigated systematically. The high-quality growth of Mn₄N films was confirmed by x-rayθ-2θ, pole figures and high-resolution transmission electron microscopy. The Mn₄N films exhibit ferrimagnetic with strong perpendicular magnetic anisotropy. The saturation magnetization of Mn₄N films decreases with increasing temperature, following the Bloch's spin wave theory. The resistivity of Mn₄N films exhibits metallic conductance mechanism. Debye temperature of Mn₄N is estimated to be 85 K. The calculated residual resistivityρ_xx0of the 78.8 nm-thick Mn₄N film is 30.56μΩ cm. The magnetoresistances of Mn₄N films display a negative signal and butterfly shape. The sign of anisotropic magnetoresistance (AMR) is positive, which infers that the AMR is dominated by the spin-up conduction electrons. Moreover, the transformation of fourfold to twofold symmetry for AMR and twofold to onefold symmetry for planar Hall resistivity is attributed to tetragonal crystal field effect.

Transition metal nitrides and their mixed crystals for spintronics

Anti-perovskite transition metal nitrides exhibit a variety of magnetic properties-such as ferromagnetic, ferrimagnetic, and paramagnetic-depending on the 3dtransition metal. Fe₄N and Co₄N are ferromagnetic at room temperature (RT), and the minority spins play a dominant role in the electrical transport properties. However, Mn₄N is ferrimagnetic at RT and exhibits a perpendicular magnetic anisotropy caused by tensile strain. Around the magnetic compensation in Mn₄N induced by impurity doping, researchers have demonstrated ultrafast current-induced domain wall motion reaching 3000 m s^-1at RT, making switching energies lower and switching speed higher compared with Mn₄N. In this review article, we start with individual magnetic nitrides-such as Fe₄N, Co₄N, Ni₄N, and Mn₄N; describe the nitrides' features; and then discuss compounds such as Fe_4-xA_xN (A = Co, Ni, and Mn) and Mn_4-xB_xN (B = Ni, Co, and Fe) to evaluate nitride properties from the standpoint of spintronics applications. We pay particular attention to preferential sites of A and B atoms in these compounds, based on x-ray absorption spectroscopy and x-ray magnetic circular dichroism.

Current-Driven Domain Wall Dynamics in Ferrimagnetic Nickel-Doped Mn4N Films: Very Large Domain Wall Velocities and Reversal of Motion Direction across the Magnetic Compensation Point

Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic phenomena allowing magnetization manipulation using electrical currents. Beyond their fundamental interest, they allow developing new classes of magnetic memories and logic devices, in particular based on domain wall (DW) motion. In this work, we report the study of STT-driven DW motion in ferrimagnetic manganese nickel nitride (Mn_4-xNi_xN) films, in which magnetization and angular momentum compensation can be obtained by the fine adjustment of the Ni content. Large domain wall velocities, approaching 3000 m/s, are measured for Ni compositions close to the angular momentum compensation point. The reversal of the DW motion direction, observed when the compensation composition is crossed, is related to the change of direction of the angular momentum with respect to that of the spin polarization. This is confirmed by the results of ab initio band structure calculations.

Heteroleptic manganese compounds as potential precursors for manganese based thin films and nanomaterials

Among the five novel synthesized manganese compounds, Mn(dmampea)(ⁱPr-MeAMD) was obtained as a highly volatile liquid compound that can be used as a precursor for manganese based thin films and nanomaterials.