S. H. Han

Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse.

Anisotropic magnetic phase diagrams of HoB4 single crystal

We have investigated the magnetic and electronic properties of a single-crystal HoB4. Antiferromagneticlike transitions were revealed by the temperature-dependent magnetization exhibiting two transition temperatures at TN1=7.1 K and TN2=5.7 K for an applied magnetic field along the c-axis, and showed only one transition at T=5.7 K for an applied magnetic field perpendicular to the c-axis. The isothermal magnetization with an applied magnetic field along the c-axis exhibited three distinct metamagnetic phase transitions at Hc1=2 T, Hc2=3.5 T, and Hc3=3.9 T at T=2 K. On the other hand, the isothermal magnetization with an applied magnetic field perpendicular to the c-axis showed two metamagneticlike transitions. A rapid change in the temperature and the field-dependent resistivity was found to be intimately correlated with magnetic transitions. Based on the isothermal magnetization and field-dependent resistivity for both magnetic field directions (H∥c and H⊥c), anisotropic phase diagrams of HoB4 were const...

Metal Oxide Nanocomposites: Advantages and Shortcomings for Application in Conductometric Gas Sensors

The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composites using in conductometric gas sensors, which should be taken into account while designing and fabricating sensors based on metal oxide composites. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

Current-induced magnetic switching with spin-orbit torque in an interlayer-coupled junction with a Ta spacer layer

Spin-orbit torque has attracted considerable attention as a means to overcome limits of devices based on spin-transfer torque. However, a small magnetic field that is collinear to the current flow must be applied to break symmetry and induce deterministic current-induced magnetization switching. Recently, a junction utilizing interlayer coupling mediated by a Ru spacer layer between two CoFe layers was designed for symmetry breaking and exhibited current-induced magnetization switching without a magnetic field. Here, we demonstrate zero-field current-induced switching of the perpendicular magnetization of a Co layer that is indirectly coupled with a CoFe layer via a Ta spacer. The weak interlayer coupling exhibited by Ta allows the layer thickness to be relatively small (≈0.5 nm), enabling appropriate interlayer coupling to induce spin-orbit torque for current-induced magnetic switching. External magnetic field effects on switching characteristics show that the current switching process is quite stable against external environments.

Field-driven dynamics and time-resolved measurement of Dzyaloshinskii-Moriya torque in canted antiferromagnet YFeO 3

Electrical spin switching in an antiferromagnet is one of the key issues for both academic interest and industrial demand in new-type spin devices because an antiferromagnetic system has a negligible stray field due to an alternating sign between sub-lattices, in contrast to a ferromagnetic system. Naturally, questions arise regarding how fast and, simultaneously, how robustly the magnetization can be switched by external stimuli, e.g., magnetic field and spin current. First, the exploitation of ultrafast precessional motion of magnetization in antiferromagnetic oxide has been studied intensively. Regarding robustness, the so-called inertia-driven switching scenario has been generally accepted as the switching mechanism in antiferromagnet system. However, in order to understand the switching dynamics in a canted antiferromagnet, excited by magnetic field, accurate equation of motion and corresponding interpretation are necessary. Here, we re-investigate the inertia-driven switching process, triggered by the strict phase matching between effective driving field, dh/dt, and antiferromagnetic order parameters, l. Such theoretical approaches make it possible to observe the static parameters of an antiferromagnet, hosting Dzyaloshinskii–Moriya (DM) interaction. Indeed, we estimate successfully static parameters, such as DM, exchange, and anisotropy energies, from dynamical behaviour in YFeO3, studied using terahertz time-domain spectroscopy.

Magnetic and electric properties and phase diagram of single crystalline TmAlB4

The magnetic and electric properties of TmAlB4 single crystals were investigated. It was found that temperature-dependent magnetization showed a large anisotropy with the c axis being easy magnetic direction. The anisotropy is likely due to crystalline electric field effect. Isothermal magnetization at T=2K represented six metamagnetic transitions at HC1=9.6kOe, HC2=12kOe, HC3=17.1kOe, HC4=21.4kOe, HC5=24.1kOe, and HC6=26kOe. Field-dependent resistivity at T=2K with the applied field along the c axis and current perpendicular to the c axis exhibited a noticeable sharp change at the fields of metamagnetic transitions, confirming the six transitions. Based on the isothermal magnetization and field-dependent resistivity at several temperatures, a field-temperature phase diagram of TmAlB4 was constructed, which contains at least seven magnetic phases.

Magnetic and electronic irreversibility and relaxation in Eu1−xLaxB6 (x=0.15 and 0.18)

We have investigated the magnetic and electronic transport properties of Eu1−xLaxB6 (x=0.15 and 0.18). Temperature-dependent magnetization of Eu1−xLaxB6 (x=0.15 and 0.18) exhibited antiferromagneticlike ground state with transition temperature Tm≈5K and thermal hysteresis below Tm between field-cooled and zero-field-cooled modes with the magnetic field of H=0.1kOe. Time dependent isothermal remnant magnetization MIRM of Eu1−xLaxB6 (x=0.15 and 0.18) was found to follow logarithmic magnetic relaxation behavior M(t)=M0−M1log(t). The temperature-dependent resistivity ρ(T) shows anomalous increase at low temperatures below T⩽20K, suppressed by magnetic field, which can be explained by magnetic polaron picture. Interestingly, field dependent electrical resistivity ρ(H) for Eu1−xLaxB6 (x=0.15 and 0.18) showed irreversibility between increasing and decreasing field. The relaxation of ρ(H→0) was found to follow the general stretched exponential form, ρ(t)=A+Bexp(−t∕τ)γ.