Experimental results of rectification of a constant wave radio frequency (RF) current flowing in a single-layered ferromagnetic wire are presented. We show that a detailed external magnetic field dependence of the RF current induced a direct-current voltage spectrum. The mechanism of the rectification is discussed in a term of the spin transfer torque, and the rectification is closely related to resonant spin wave excitation with the assistant of the spin-polarized RF current. The micromagnetic simulation taking into account the spin transfer torque provides strong evidence which supports the generation of spin wave excitation by the RF current.
We report the rectifying effect of a constant-wave radio frequency (RF) current by a magnetic domain wall (DW) on a single-layered ferromagnetic wire. A direct-current (DC) voltage is generated by the spin torque diode effect, which is a consequence of magnetoresistance oscillation due to the resonant spin wave excitation induced by the spin-polarized RF current. The DC voltage spectrum strongly depends on the internal spin structure in the DW, which corresponds to the magnetic fingerprint of the spin structure in the ferromagnetic wire.
We predict that the Curie temperature of a ferromagnetic resonant tunneling diode will decrease abruptly, by approximately a factor of two, when the downstream chemical potential falls below the quantum well resonance energy. This property follows from elementary quantum transport theory notions combined with a mean field description of diluted magnetic semiconductor ferromagnetism. We illustrate this effect by solving coupled non-equilibrium Green's function, magnetic mean-field, and electrostatic Poisson equations self-consistently to predict the bias voltage and temperature dependence of th…
The electromotive forces induced by surface acoustic waves (SAWs) are investigated in ferromagnetic thin films. CoFeB thin films deposited on LiNbO$_3$ substrates are patterned into Hall-bars to study the acoustoelectric transport properties of the device. The longitudinal and transverse dc voltages that develop in the Hall bars, which are parallel and orthogonal to the flow of the SAW, respectively, are measured under application of an in-plane magnetic field. The longitudinal voltage scales linearly with the SAW power and reverses its polarity upon changing the direction to which the SAW pro…
We employ optical pump-probe spectroscopy to investigate the voltage dependence of spontaneous electron and nuclear spin polarizations in hybrid MnAs/n-GaAs and Fe/n-GaAs Schottky diodes. Through the hyperfine interaction, nuclear spin polarization that is imprinted by the ferromagnet acts on conduction electron spins as an effective magnetic field. We demonstrate tuning of this nuclear field from <0.05 to 2.4 kG by varying a small bias voltage across the MnAs device. In addition, a connection is observed between the diode turn-on and the onset of imprinted nuclear polarization, while traditio…
Spin pumping by a moving magnetization gives rise to an electric voltage over a spin valve. Thermal fluctuations of the magnetization manifest themselves as increased thermal voltage noise with absorption lines at the ferromagnetic resonance frequency and/or zero frequency. The effect depends on the magnetization configuration and can be of the same order of magnitude as the Johnson-Nyquist thermal noise. Measuring colored voltage noise is an alternative to ferromagnetic resonance experiments for nano-scale ferromagnetic circuits.
The broadband ferromagnetic resonance measurement using the rectifying effect of Ni81Fe19 wire has been investigated. One wire is deposited on the center strip line of the coplanar waveguide (CPW) and the other one deposited between two strip lines of CPW. The method is based on the detection of the magnetoresistance oscillation due to the magnetization dynamics induced by the radio frequency field. The magnetic field dependences of the resonance frequency and the rectification spectrum are presented and analytically interpreted on the standpoint of a uniform magnetization precession model.
The electrical control of the magnetization switching in ferromagnets is highly desired for future spintronic applications. Here we report on hybrid piezoelectric (PZT) /ferromagnetic (Co2FeAl) devices in which the planar Hall voltage in the ferromagnetic layer is tuned solely by piezo voltages. The change of planar Hall voltage is associated with magnetization switching through 90 in the plane under piezo voltages. Room temperature magnetic NOT and NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar Hall effect devices without the external magnetic field. Our demon…
We demonstrate numerically the existence of a spin-motive force acting on spin-carriers when moving in a time and space dependent internal field. This is the case of electrons in a one-dimensional wires with a precessing domain wall. The effect can be explained solely by considering adiabatic dynamics and it is shown to exist for both classical and quantum systems.
Magnetic skyrmions have potential applications in next-generation spintronics devices with ultralow energy consumption. In this work, the current-driven skyrmion motion in a narrow ferromagnetic nanotrack with voltage-controlled magnetic anisotropy (VCMA) is studied numerically. By utilizing the VCMA effect, the transport of skyrmion can be unidirectional in the nanotrack, leading to a one-way information channel. The trajectory of the skyrmion can also be modulated by periodically located VCMA gates, which protects the skyrmion from destruction by touching the track edge. In addition, the loc…
We present a theoretical study of heat transport in electrically insulating ferromagnetic wires containing a domain wall. In the regime of validity of continuum micromagnetism a domain wall is found to have no effect on the heat conductance. However, spin waves are found to be reflected by domain walls with widths of a few lattice spacings, which is associated with emergence of an additional spin wave bound state. The resulting domain wall heat conductance should be significant for thin films of Yttrium Iron Garnet with sharply defined magnetic domains.
We carried out a concerted effort to determine the absolute sign of the inverse spin Hall effect voltage generated by spin currents injected into a normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room temperature, generating spin currents by microwaves and temperature gradients. We find consistent results for different samples and measurement setups that agree with theory. We suggest a right-hand-rule to define a positive spin Hall angle corresponding to with the voltage expected for the simple case of scattering of free electrons from repulsive Coulomb charges.
We investigate the current-excited magnetization dynamics in a narrow ferromagnetic Permalloy wire by means of Lorentz microscopy, together with the results of simultaneous transport measurements. A detailed structural evolution of the magnetization is presented as a function of the applied current density. Local structural deformation, bidirectional displacement, and magnetization reversal are found below the Curie temperature with increasing the current density. We discuss probable mechanisms of observed features of the current-excited magnetization dynamics.
The radio-frequency (RF) voltage amplification property of a tunnel magnetoresistance device driven by an RF external-magnetic-field-induced ferromagnetic resonance was studied. The proposed device consists of a magnetic tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The input RF voltage applied to the waveguide can excite the resonant dynamics in the free layer magnetization, leading to the generation of an output RF voltage under a DC bias current. The dependences of the RF voltage gain on the static external magnetic field strength and angle were systematically inves…
A ferromagnet can resonantly absorbs rf radiation to sustain a steady precession of the magnetization around an internal or applied magnetic field. We show that under these ferromagnetic resonance (FMR) conditions, a dc voltage is generated at a normal-metal electric contact to a ferromagnet with spin-flip scattering. This mechanism allows an easy electric detection of magnetization dyamics.
We develop a method for universally resolving the important issue of separating spin pumping (SP) from spin rectification (SR) signals in bilayer spintronics devices. This method is based on the characteristic distinction of SP and SR, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices …
We demonstrate dynamic voltage control of the magnetic anisotropy of a (Ga,Mn)As device bonded to a piezoelectric transducer. The application of a uniaxial strain leads to a large reorientation of the magnetic easy axis which is detected by measuring longitudinal and transverse anisotropic magnetoresistance coefficients. Calculations based on the mean-field kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the measured effect. Electrically induced magnetization switching and detection of unconventional crystalline components of the anisotropic magnetoresistance are prese…
An anomalous Hall effect and rectification of a Hall voltage are observed by applying a radio-frequency (rf) current through a single-layered ferromagnetic wire located on a coplanar waveguide. The components of the magnetization precession, both in and perpendicular to the plane, can be detected via the Hall voltage rectification of the rf current by incorporating an additional direct (dc) current. In this paper, we propose a phenomenological model, which describes the time-dependent anisotropic magnetoresistance and time-dependent planer Hall effect. The nonlinearity of the spin dynamics acc…
We investigate the current-driven magnetization dynamics in narrow Permalloy wires by means of Lorentz microscopy and electron holography. Current pulses are found to transform the magnetic structure in the uniformly magnetized state below the Curie temperature. A variety of magnetic states including reversed magnetic domains are randomly obtained in low probability. The dynamics of vortices found in most of observed magnetic states seems to play a key role in triggering the magnetization reversal.
We study current-induced domain-wall motion in a narrow ferromagnetic wire. We propose a way to move domain walls with a resonant time-dependent current which dramatically decreases the Ohmic losses in the wire and allows to drive the domain wall with higher speed without burning the wire. For any domain wall velocity we find the time-dependence of the current needed to minimize the Ohmic losses. Below a critical domain-wall velocity specified by the parameters of the wire the minimal Ohmic losses are achieved by dc current. Furthermore, we identify the wire parameters for which the losses red…
We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottk…
The rectifying effect of radio-frequency (RF) current is highly sensitive in terms of the spatial spin distribution and dynamics. It emerged that an additional spin wave mode was stimulated by the direct-current (DC) current and that this spin wave was detectable via rectification of the RF current. A phenomenological model to describe the time-dependent anisotropic magnetoresistance or time-dependent planer Hall effect is proposed and found to correlate well to the experimental results. The nonlinear spin dynamics accompanying additional spin waves are studied as functions of the RF and DC cu…
We investigated the microwave-assisted DC voltages of ferromagnetic resonances and exchangedominated standing spin wave excitations in two different in-plane magnetized permalloy thin films via homodyne detection. The line shapes of ferromagnetic resonance spectra and the dispersion curves of ferromagnetic resonance and standing spin wave are in agreement of previous studies, while further investigations of DC voltage spectra for these two excitations reveal that 1. unlike ferromagnetic resonance signals, the anti-symmetrical line shapes of standing spin wave excitations are not depend on the …
As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e. the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy meta…
We calculate the linear and nonlinear conductance of spinless fermions in clean, long quantum wires where short-ranged interactions lead locally to equilibration. Close to the quantum phase transition where the conductance jumps from zero to one conductance quantum, the conductance obtains an universal form governed by the ratios of temperature, bias voltage and gate voltage. Asymptotic analytic results are compared to solutions of a Boltzmann equation which includes the effects of three-particle scattering. Surprisingly, we find that for long wires the voltage predominantly drops close to one…
We study how the shape of the spinwave resonance lines in rf-voltage induced FMR can be used to extract the spinwave density of states and the damping within the precessing layer in nanoscale tunnel junctions that possess perpendicular anisotropy. We work with a field applied along the easy axis to preserve the uniaxial symmetry of the system. We describe the set-up to study the susceptibility contributions of the spin waves in the field-frequency space. We then identify the maximum device size above which the spinwaves can no longer be studied in isolation as the linewidths of their responses…
For spin-polarized junctions of ferromagnetically contacting multiple conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon nanotubes/FM junctions, we theoretically investigate spin-dependent transport to elucidate the intrinsic relation between the number of paths and conduction, and to enhance the magnetoresistance (MR) ratio. When many paths are randomly located between the two FMs, electronic wave interference between the FMs appears, and then the MR ratio increases with increasing number of paths. Furthermore, at each number of paths, the MR ratio for carbon nanotubes b…
We investigated the spin-dependent transport properties of a lateral spin-valve device with a 600 nm-long GaAs channel and ferromagnetic MnGa electrodes with perpendicular magnetization. Its current-voltage characteristics show nonlinear behavior below 50 K, indicating that tunnel transport through the MnGa/GaAs Schottky barrier is dominant at low temperatures. We observed clear magnetoresistance (MR) ratio up to 12% at 4 K when applying a magnetic field perpendicular to the film plane. Furthermore, a large spin-dependent output voltage of 33 mV is obtained. These values are the highest in lat…
In this paper we analyze different contributions to the magnetoresistance of magnetic tunneling junctions at low voltages. A substantial fraction of the resistance drop with voltage can be ascribed to variations of the density of states and the barrier transmission with the bias. However, we found that the anomaly observed at zero bias and the magnetoresistance behavior at very small voltages, point to the contribution of inelastic magnon-assisted tunneling. The latter is described by a transfer parameter $T^{J}$, which is one or two orders of magnitude smaller than $T^{d}$, the direct transmi…
The large tunneling anisotropic magneto-resistance of a single $p^{++}$-(Ga,Mn)As/$n^{+}$-GaAs Zener-Esaki diode is evidenced in a perpendicular magnetic field over a large temperature and voltage range. Under an applied bias, the tunnel junction transparency is modified, allowing to continuously tune anisotropic transport properties between the tunneling and the ohmic regimes. Furthermore, an asymmetric bias-dependence of the anisotropic tunneling magneto-resistance is also observed: a reverse bias highlights the full (Ga,Mn)As valence band states contribution, whereas a forward bias only pro…
We study current induced magnetization dynamics in a long thin ferromagnetic wire with Dzyaloshinskii-Moriya interaction (DMI). We find a spiral domain wall configuration of the magnetization and obtain an analytical expression for the width of the domain wall as a function of the interaction strengths. Our findings show that above a certain value of DMI a domain wall configuration cannot exist in the wire. Below this value we determine the domain wall dynamics for small currents, and calculate the drift velocity of the domain wall along the wire. We show that the DMI suppresses the minimum va…
We study nonequilibrium quantum transport through a mesoscopic wire coupled via local exchange to a ferromagnetic spin chain. Using the Keldysh formalism in the self-consistent Born approximation, we identify fingerprints of the magnetic polaron state formed by hybridization of electronic and magnon states. Because of its low decoherence rate, we find coherent transport signals. Both elastic and inelastic peaks of the differential conductance are discussed as a function of external magnetic fields, the polarization of the leads and the electronic level spacing of the wire.
We predict the electrical generation and injection of domain walls into a ferromagnetic nano-wire without the need of an assisting magnetic field. Our theory shows that above a critical current $j_{c}$ domain walls are injected into the nano-wire with a period $T\sim (j-j_{c})^{-1/2}$. In a uniaxial anisotropy geometry this process does not require Dzyaloshinskii-Moria or dipole-dipole interaction and can be done in a simple exchange ferromagnet. We also show that this process and the period exponents are universal and do not depend on the peculiarities of the microscopic Hamiltonian.
We investigate the behavior of the four-terminal resistance $R_{4pt}$ in a quantum wire described by a Luttinger liquid in two relevant situations: (i) in the presence of a single impurity within the wire and (ii) under the effect of asymmetries introduced by dirty voltage probes. In the first case, interactions leave a signature in a power law behavior of $R_{4pt}$ as a function of the voltage $V$ and the temperature $T$. In the second case interactions tend to mask the effect of the asymmetries. In both scenarios the occurrence of negative values of $R_{4pt}$ is explained in simple terms.
In this study, a model of a Schottky-barrier carbon nanotube field- effect transistor (CNT-FET), with ferromagnetic contacts, has been developed. The emphasis is put on analysis of current-voltage characteristics as well as shot (and thermal) noise. The method is based on the tight-binding model and the non- equilibrium Green's function technique. The calculations show that, at room temperature, the shot noise of the CNT FET is Poissonian in the sub-threshold region, whereas in elevated gate and drain/source voltage regions the Fano factor gets strongly reduced. Moreover, transport properties …
The response of a mesoscopic homogeneous superconducting wire, connected with bulk normal metal reservoirs, is theoretically investigated as function of the applied voltage. The finite relaxation length of the nonequilibrium quasiparticle distribution function $\bar{L_E}$ is included where we assumed that our wire is in the dirty limit. We found that {\it both} symmetric and asymmetric states can exist which are characterized by a stationary symmetric and asymmetric distribution of the order parameter with respect to the center of the wire. Current voltage characteristics of the wire with leng…
We calculate the distribution of the conductance G in a one-dimensional disordered wire at finite temperature T and bias voltage V in a independent-electron picture and assuming full coherent transport. At high enough temperature and bias voltage, where several resonances of the system contribute to the conductance, the distribution P(G(T,V)) can be represented with good accuracy by autoconvolutions of the distribution of the conductance at zero temperature and zero bias voltage. The number of convolutions depends on T and V. In the regime of very low T and V, where only one resonance is relev…
Magneto-ionics has emerged as a promising approach to manipulate magnetic properties, not only by drastically reducing power consumption associated with electric current based devices but also by enabling novel functionalities. To date, magneto-ionics have been mostly explored in oxygen-based systems, while there is a surge of interests in alternative ionic systems. Here we demonstrate highly effective hydroxide-based magneto-ionics in electrodeposited $α$-Co(OH)$_{2}$ films. The $α$-Co(OH)$_{2}$, which is a room temperature paramagnet, is switched to ferromagnetic after electrolyte gating wit…
We describe electrical detection of spin pumping in metallic nanostructures. In the spin pumping effect, a precessing ferromagnet attached to a normal-metal acts as a pump of spin-polarized current, giving rise to a spin accumulation. The resulting spin accumulation induces a backflow of spin current into the ferromagnet and generates a dc voltage due to the spin dependent conductivities of the ferromagnet. The magnitude of such voltage is proportional to the spin-relaxation properties of the normal-metal. By using platinum as a contact material we observe, in agreement with theory, that the v…
We study the effect of bias voltage on the nuclear spin polarization of a ballistic wire, which contains electrons and nuclei interacting via hyperfine interaction. In equilibrium, the localized nuclear spins are helically polarized due to the electron-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Focusing here on non-equilibrium, we find that an applied bias voltage induces a uniform polarization, from both helically polarized and unpolarized spins available for spin flips. Once a macroscopic uniform polarization in the nuclei is established, the nuclear spin helix rotates with f…
Magnetic resonances driven by current-induced torques are crucial tools to study magnetic materials but are very limited in frequency and mechanical efficiency. We propose an alternative mechanism, voltage-induced torque, to realize high efficiency in generating high-frequency magnetization dynamics. When a ferromagnet-topological insulator-ferromagnet trilayer heterostructure is operated as an adiabatic quantum motor, voltage-induced torque arises from the adiabatic motion of gapped topological electrons on the two interfaces and act oppositely on the two ferromagnetic layers, which can excit…
We consider a wire network of ferromagnetic impurities on the surface of an $s$-wave superconductor with strong Rashba spin-orbit interaction. Within the topological phase, zero-energy Majorana fermions appear at wire end-points as well as at junctions between an odd number of wire segments, while no low-energy states are present at junctions between an even number of wire segments, providing strong experimentally accessible signatures for Majorana fermions. We also investigate the quasiparticle energy gap with respect to varying the Rashba spin-orbit coupling and magnetic impurity strength.
We present a theoretical analysis of current driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet tri-layer. This method of driving ferromagnetic resonance was recently realized experimentally by Tulapurkar et al. [Nature 438, 339 (2005)] and Sankey et al. [Phys. Rev. Lett. 96, 227601 (2006)]. The precessing magnetization rectifies the alternating current applied to drive the ferromagnetic resonance and leads to the generation of a dc voltage. Our analysis shows that a second mechanism to generate a dc voltage, rectification of spin currents emitted by the precessing magnet…
We present a quantitative study of the current-voltage characteristics (CVC) of SFIFS Josephson junctions (S denotes bulk superconductor, F - metallic ferromagnet, I - insulating barrier) with weak ferromagnetic interlayers in the diffusive limit. The problem is solved in the framework of the nonlinear Usadel equations. We consider the case of a strong tunnel barrier such that the left SF and the right FS bilayers are decoupled. We calculate the density of states (DOS) in SF bilayers using a self-consistent numerical method. Then we obtain the CVC of corresponding SFIFS junctions, and discuss …
We theoretically investigate the effect of the negative differential conductance of a ferromagnetic barrier on the surface of a topological insulator. Due to the changes of the shape and position of the Fermi surfaces in the ferromagnetic barrier, the transport processes can be divided into three kinds: the total, partial and blockade transmission mechanisms. The bias voltage can give rise to the transition of the transport processes from partial to blockade transmission mechanisms, which results in a giant effect of negative differential conductance. With appropriate structural parameters, th…
The temperature and voltage dependence of spin transport is theoretically investigated in a new type of magnetic tunnel junction, which consists of two ferromagnetic outer electrodes separated by a ferromagnetic barrier and a nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic barrier, which plays an important role at finite temperature, is included by taking the mean-field approximation. It is found that, the tunnel magnetoresistance (TMR) and the electron-spin polarization depend strongly on the temperature and the applied voltage. The TMR and spin polarization at di…
The spin-Seebeck effect refers to voltage signals induced in metals by thermally driven spin currents in adjacent magnetic systems. We present a theory of the spin-Seebeck signal in the case where the conductor that supports the voltage signal is the topologically protected two-dimensional surface-state system at the interface between a ferromagnetic insulator (FI) and a topological insulator (TI). Our theory uses a Dirac model for the TI surface-states and assumes Heisenberg exchange coupling between the TI quasiparticles and the FI magnetization. The spin-Seebeck voltage is induced by the TI…
A puzzle arising from Faraday's law is considered and solved concerning the question which voltage is induced in an open wire with a time-varying homogeneous magnetic field. In contrast to closed wires where the voltage is determined by the time variance of magnetic field and enclosed area, in an open wire we have to integrate the electric field along the wire. It is found that the longitudinal electric field contributes with 1/3 and the transverse field with 2/3 to the induced voltage. In order to find the electric fields the sources of the magnetic fields are necessary to know. The represent…
We study spin transport in normal/ferromagnetic/normal graphene junctions where a gate electrode is attached to the ferromagnetic graphene. We find that due to the exchange field of the ferromagnetic graphene, spin current through the junctions has an oscillatory behavior with respect to the chemical potential in the ferromagnetic graphene, which can be tuned by the gate voltage. Especially, we obtain a controllable spin current reversal by the gate voltage. Our prediction of high controllability of spin transport in ferromagnetic graphene junction may contribute to the development of the spin…
We consider interaction effects related to a nonuniform magnetization in ferromagnetic nanowires and their possible generalization to nanorings. First we show that the electric current in a ferromagnetic nanowire with more than one domain wall induces an exchange coupling between the walls mediated by the spin-dependent interference of scattered carriers. This interaction reveals a complex behavior as a function of mutual orientations and separation of the domain walls, thus affecting the domain wall dynamics. Then we consider how the theory should be modified in the case of a magnetized quant…
We analyze the change in the resistance of a junction between a diffusive ferromagnetic (F) wire and normal metal electrode, due to the onset of superconductivity (S) in the latter and a double Andreev scattering process leading to a complete internal reflection of a large fraction of the spin-polarized electrons back into the ferromagnet. The superconducting transition results in an additional contact resistance arising from the necessity to match spin-polarized current in F-wire to spin-less current in S-reservoir, which is comparable to the resistance of a piece of a F-wire with the length …
We predict the electrical generation and injection of domain walls into a ferromagnetic nano-wire without the need of an assisting magnetic field. Our analytical and numerical results show that above a critical current $j_{c}$ domain walls are injected into the nano-wire with a period $T \sim (j-j_{c})^{-1/2}$. Importantly, domain walls can be produced periodically even in a simple exchange ferromagnet with uniaxial anisotropy, without requiring any standard "twisting" interaction like Dzyaloshinskii-Moriya or dipole-dipole interactions. We show analytically that this process and the period ex…
We present a versatile method for detecting the presence and motion of a trapped domain wall in a narrow ferromagnetic layer using current-perpendicular-to-plane (CPP) giant magnetoresistance (MR). The CPP-MR response to small motions of the trapped domain wall is enhanced because the CPP current is restricted to the region of wall trapping. We use a Permalloy/Cu/Permalloy spin valve in the shape of a long, ~500-nm-wide wire with a constriction (notch) near its middle that acts as a trapping site for a head-to-head domain wall. Two different notch shapes were studied, mostly at 4.2 K but also …
A phenomenological approach based on the principle of minimum heat generation is proposed for understanding experiments for metallic wires with a ferromagnetic domain wall controlled by a magnetic field. This approach elucidates the origin of negative jump and of hysteresis in the magnetoresistance experiments. To justify our approach, we computed the transmission probability of a single electron through a wire. Under certain conditions, the presence of a domain wall enhances the transmission through an impurity potential. Combining this result with the principle of minimum heat generation exp…
In a recent Letter [Appl. Phys. Lett. 87, 103104 (2005)], Yoshida et al. report that nonlinearities in current-voltage curves of gold quantum point contacts occur as a result of a shortening of the distance between electrodes at finite bias, presumably due to thermal expansion. For short wires, the electrode displacement induces a thickening of the wire, as well as nonlinearities of the IV curve, while the radius of long wires is left unchanged, thus resulting in a linear IV curve. We argue here that electron shell effects, which favor wires with certain "magic radii," prevent the thickening o…
A domain wall in a ferromagnetic one-dimensional nanowire experiences current induced motion due to its coupling with the conduction electrons. When the current is not sufficient to drive the domain wall through the wire, or it is confined to a perpendicular layer, it nonetheless experiences oscillatory motion. In turn, this oscillatory motion of the domain wall can couple resonantly with the electrons in the system affecting the transport properties further. We investigate the effect of the coupling between these domain wall modes and the current electrons on the transport properties of the s…
We propose a ferromagnetic spintronic system, which consists of two serial connected resonant tunneling diodes. One diode is nonmagnetic whereas the other comprises a ferromagnetic emitter and quantum well. Using a selfconsistent coherent transport model we show that the current-voltage characteristic of the ferromagnetic diode can be strongly modulated by changing the relative orientation of the magnetizations in the emitter and quantum well, respectively. By a continuous change of the relative magnetization angle the total resistance exhibits a discrete jump realizing digital magneto resista…
The current mediated domain-wall dynamics in a thin ferromagnetic wire is investigated. We derive the effective equations of motion of the domain wall. They are used to study the possibility to optimize the power supplied by electric current for the motion of domain walls in a nanowire. We show that a certain resonant time-dependent current moving a domain wall can significantly reduce the Joule heating in the wire, and thus it can lead to a novel proposal for the most energy efficient memory devices. We discuss how Gilbert damping, non-adiabatic spin transfer torque, and the presence of Dzyal…
We consider resonant transmission through a finite-length quantum wire connected to leads via finite transparency junctions. The coherent electron transport is strongly modified by the Coulomb interaction. The low-temperature current-voltage ($IV$) curves show step-like dependence on the bias voltage determined by the distance between the quantum levels inside the conductor, the pattern being dependent on the ratio between the charging energy and level spacing. If the system is tuned close to the resonance condition by the gate voltage, the low-voltage $IV$ curve is Ohmic. At large Coulomb ene…
The electrical detection of spin torque ferromagnetic resonance (st-FMR) is becoming a popular method for measuring the spin-Hall angle of heavy metals (HM). However, various sensible analysis on the same material with either the same or different experimental setups yielded different spin-Hall angles with large discrepancy, indicating some missing ingredients in our current understanding of st-FMR. Here we carry out a careful analysis of electrical signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary magnetic anisotropy. The FM magnetization is driven by two radio-frequ…
