Search

We suggest coherent switching of canted antiferromagnetic (AFM) spins using spin-orbit torque (SOT) in a small magnet. The magnetic system of orthoferrite features biaxial easy anisotropy and the Dzyaloshinskii-Moriya interaction, which is perpendicular to the easy axes and therefore creates weak magnetization $(\mathbit{m})$. A dampinglike component of the SOT induces N\'eel reorientation along one of the easy axes and then exerts torque on $\mathbit{m}$, leading to tilting of the N\'eel order $\mathbit{l}$. The torque on the magnetization becomes stronger due to coupling with the induced Oersted field or the fieldlike component of the SOT, enhancing the tilting of $\mathbit{l}$. Therefore, $\mathbit{l}$ is found to experience deterministic switching after the SOT is turned off. Based upon both numerical and analytical analysis of the coherent switching, exclusive OR (XOR) logic gates are also found to be implemented in a single magnetic layer. In addition, we investigate how magnetic parameters affect the critical reorientation angle and current density in a simple layered structure of platinum and a canted AFM. Our findings are expected to provide an alternative spin-switching mechanism for ultrafast applications such as spin logic and electronic devices.

Antiferromagnetic insulators (AFIs) have attracted much interest from many researchers as promising candidates for use in ultrafast, ultralow-dissipation spintronic devices. As a fast method of reversing magnetization, precessional switching is realized when antiferromagnetic N\'eel orders $l=({\mathbf{s}}_{1}+{\mathbf{s}}_{2})/2$ surmount the magnetic anisotropy or potential barrier in a given magnetic system, which is described well by the antiferromagnetic plane pendulum (APP) model. Here, we report that, as an alternative switching scenario, the direct coupling of an electric field with Dzyaloshinskii-Moriya (DM) interaction, which stems from spin-orbit coupling, is exploited for optimal switching. We derive the pendulum equation of motion of antiferromagnets, where DM torque is induced by a pulsed electric field. The temporal DM interaction is found to not only be in the form of magnetic torques (e.g., spin-orbit torque or magnetic field) but also modifies the magnetic potential that limits $l$ 's activity; as a result, appropriate controls (e.g., direction, magnitude, and pulse shape) of the induced DM vector realize deterministic reversal in APP. The results present an approach for the control of a magnetic storage device by means of an electric field.

Detailed resistivity measurements were made along the planes of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ single crystals in zero field and in the temperature region above the superconducting transition temperature ${T}_{c}.$ Analyses of the fluctuation conductivity \ensuremath{\Delta}\ensuremath{\sigma} are presented using a careful construction of the mean-field critical temperature ${T}_{c}^{\mathrm{mf}}.$ \ensuremath{\Delta}\ensuremath{\sigma} can be described by the Lawrence-Doniach model with a two-dimensional (2D)-3D crossover close to ${T}_{c}^{\mathrm{mf}}.$ The $c$-axis coherence length was found to be 0.9\ifmmode\pm\else\textpm\fi{}0.1 \AA{}. For comparison \ensuremath{\Delta}\ensuremath{\sigma} was also calculated from ${T}_{c}$ defined from the peak temperature of $d\ensuremath{\rho}/dT.$ It is shown that a consistent description of the 2D-3D transition is then lost.

We report magnetoresistance $R(H)$ and current-voltage $I\ensuremath{-}V$ measurements in the superconducting mixed state of ${\mathrm{CeRu}}_{2}$ ${(T}_{c}=6.1\mathrm{K}).$ A crossover in the dynamics of the magnetic flux-line lattice is observed, which could be related to the onset of the ``peak effect'' enhancement of the critical current density that occurs near the upper critical field ${H}_{c2}.$ In addition, the transport properties are dependent on the history of magnetic field and temperature cycling through the peak effect region.

In-plane ({rho}{sub ab}) and out-of-plane ({rho}{sub c}) resistivities of Y{sub 1{minus}x}Pr{sub x}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} have been determined using the electrical contact configuration of the dc flux transformer. {rho}{sub c}(x) varies nonmonotonically with x: {rho}{sub c}(x) increases at low x, reaches a maximum at x{approx}0.42, and then decreases for higher values of x. In contrast, {rho}{sub ab}(x) increases monotonically with x. These results, along with the coexistence of metallic {rho}{sub ab} and semiconducting {rho}{sub c}, are consistent with the presence of a gap in the energy spectrum of the CuO chains, leading to tunneling through both valence and conduction bands of the CuO chains. {copyright} {ital 1997} {ital The American Physical Society}

A structural aspect of the hole ordering phenomenon in the La{sub 2{minus}{ital x}}{ital M}{sub {ital x}}NiO{sub 4} ({ital x}=1/3, and {ital M}=Ca, Sr, or Ba) system has been investigated by means of x-ray diffraction experiments and measurements of the hydrostatic pressure dependence of the hole ordering temperature {ital T}{sub {ital c}}. No significant change of the average lattice parameters was found near {ital T}{sub {ital c}}, which is consistent with previous arguments that the origin of the ordering is electronic or magnetic in nature. The electrical resistivity conforms to variable range hopping behavior at low temperatures far below {ital T}{sub {ital c}} and the associated thermal activation energy shows a linear pressure dependence. The highest {ital T}{sub {ital c}} at ambient pressure was achieved with Sr doping. The pressure dependence of {ital T}{sub {ital c}} is positive for {ital M}=Ba, negative for {ital M}=Ca, and very small and negative for {ital M}=Sr. The doping and pressure dependences of {ital T}{sub {ital c}} are examined in the context of the coupling between the holes and the crystal lattice. We suggest that there is an optimum distance of 5.42 A between the nearest-neighbor ordered holes which gives the maximum {ital T}{sub {italmore » c}}.« less

The maximum value [Delta] of the negative Hall resistivity [rho][sub [ital xy]] of Y[sub 1[minus][ital x]]Pr[sub [ital x]]Ba[sub 2]Cu[sub 3]O[sub 7[minus][delta]] (0[le][ital x][approx lt]0.13) and YBa[sub 2]Cu[sub 3]O[sub [ital y]] (6.73[approx lt][ital y][le]6.84) single crystals scales with [ital T]/[ital T][sub [ital c]], exhibiting a maximum [Delta][sub max] for [ital T]/[ital T][sub [ital c]][approx]0.96 and vanishing for [ital T]/[ital T][sub [ital c]][approx lt]0.87. [Delta][sub max] scales with [ital T][sub [ital c]] and decreases monotonically with decreasing [ital T][sub [ital c]] to zero for [ital T][sub [ital c]][approx lt]70 K. The Hall conductivity [sigma][sub [ital xy]] vs [ital B] data have been analyzed using the expression [sigma][sub [ital xy]]=[ital C][sub 1]/[ital B]+[ital C][sub 2][ital B], where the two terms are associated with motion of the magnetic vortices and the quasiparticles in the vortex cores, respectively, yielding [ital C][sub 1] and [ital C][sub 2] as functions of [ital x], [ital y], and [ital T].

The anisotropic superconducting-state thermodynamic parameters of the electron-doped compound ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ have been derived from reversible dc magnetization M(H,T) measurements on magnetically aligned single-crystal particles of the compound for magnetic fields applied perpendicular and parallel to the ab plane. A recent model developed by Hao et al., which describes M(H,T) over the entire field region between ${\mathit{H}}_{\mathit{c}1}$ and ${\mathit{H}}_{\mathit{c}2}$, was used to analyze the M(H,T) data. The analysis of the measurements provides a self-consistent test of the model and resolves a controversy by showing that the anisotropy of ${\mathit{H}}_{\mathit{c}2}$(T) of the electron-doped compound ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ is comparable to that of the hole-doped compound ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$.

The upper critical field ${\mathit{H}}_{\mathit{c}2}$(T) for the magnetic field applied parallel to the c axis of a ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ single crystal has been determined from an analysis of magnetoresistance data in terms of the Ginzburg-Landau fluctuation theory for layered superconductors. The fluctuations are predominantly two dimensions (2D) away from ${\mathit{T}}_{\mathit{c}}$(H) with a crossover to 3D as ${\mathit{T}}_{\mathit{c}}$(H) is approached. The ${\mathit{H}}_{\mathit{c}2}$(T) curve shows negative curvature and is in excellent agreement with the Werthamer, Helfand, Hohenberg, and Maki theory for conventional superconductors without paramagnetic limiting effects. The values of the initial slope (${\mathit{dH}}_{\mathit{c}2}$/dT${)}_{\mathit{T}\mathit{c}}$=-7.38 kOe/K, coherence length \ensuremath{\xi}(0)=48.4 \AA{}, and orbital critical field ${\mathit{H}}_{\mathit{c}2}$(0)=97.6 kOe, derived from this analysis, are in good agreement with the values we previously obtained from fits of the Hao-Clem variational model to reversible magnetization data below ${\mathit{T}}_{\mathit{c}}$.