arXiv subjects

Ya. B. Bazaliy

Publications and source records attributed to Ya. B. Bazaliy.

31 records · Page 2Linked to original sources

arXiv2007

Slonczewski windmill with dissipation and asymmetry

J. Slonczewski invented spin-transfer effect in layered systems in 1996. Among his first predictions was the regime of ``windmill motion'' of a perfectly symmetric spin valve where the magnetizations of the layers rotate in a fixed plane keeping the angle between them constant. Since ``windmill'' was predicted to happen in the case of zero magnetic anisotropy, while in most experimental setups the anisotropy is significant, the phenomenon was not a subject of much research. However, the behavior of the magnetically isotropic device is related to the interesting question of current induced ferromagnetism and is worth more attention. Here we study the windmill regime in the presence of dissipation, exchange interaction, and layer asymmetry. It is shown that the windmill rotation is almost always destroyed by those effects, except for a single special value of electric current, determined by the parameters of the device.

cond-mat.mtrl-sci↗

arXiv2007

Generation of microwave radiation in planar spin-transfer devices

Current induced precession states in spin-transfer devices are studied in the case of large easy plane anisotropy (present in most experimental setups). It is shown that the effective one-dimensional planar description provides a simple qualitative understanding of the emergence and evolution of such states. Switching boundaries are found analytically for the collinear device and the spin-flip transistor. The latter can generate microwave oscillations at zero external magnetic field without either special functional form of spin-transfer torque, or ``field-like'' terms, if Gilbert constant corresponds to the overdamped planar regime.

cond-mat.mtrl-sci↗

arXiv2007

Extremal transmission at the Dirac point of a photonic band structure

We calculate the effect of a Dirac point (a conical singularity in the band structure) on the transmission of monochromatic radiation through a photonic crystal. The transmission as a function of frequency has an extremum at the Dirac point, depending on the transparencies of the interfaces with free space. The extremal transmission $T_{0}=Γ_{0} W/L$ is inversely proportional to the longitudinal dimension $L$ of the crystal (for $L$ larger than the lattice constant and smaller than the transverse dimension $W$). The interface transparencies affect the proportionality constant $Γ_{0}$, and they determine whether the extremum is a minimum or a maximum, but they do not affect the ``pseudo-diffusive'' 1/L dependence of $T_{0}$.

physics.optics↗

arXiv2007

Planar spin-transfer device with a dynamic polarizer

In planar nano-magnetic devices magnetization direction is kept close to a given plane by the large easy-plane magnetic anisotropy, for example by the shape anisotropy in a thin film. In this case magnetization shows effectively in-plane dynamics with only one angle required for its description. Moreover, the motion can become overdamped even for small values of Gilbert damping. We derive the equations of effective in-plane dynamics in the presence of spin-transfer torques. The simplifications achieved in the overdamped regime allow to study systems with several dynamic magnetic pieces (``free layers''). A transition from a spin-transfer device with a static polarizer to a device with two equivalent magnets is observed. When the size difference between the magnets is less than critical, the device does not exhibit switching, but goes directly into the ``windmill'' precession state.

cond-mat.mtrl-sci↗

arXiv2007

Effective attraction induced by repulsive interaction in a spin-transfer system

In magnetic systems with dominating easy-plane anisotropy the magnetization can be described by an effective one dimensional equation for the in-plane angle. Re-deriving this equation in the presence of spin-transfer torques, we obtain a description that allows for a more intuitive understanding of spintronic devices' operation and can serve as a tool for finding new dynamic regimes. A surprising prediction is obtained for a planar ``spin-flip transistor'': an unstable equilibrium point can be stabilized by a current induced torque that further repels the system from that point. Stabilization by repulsion happens due to the presence of dissipative environment and requires a Gilbert damping constant that is large enough to ensure overdamped dynamics at zero current.

cond-mat.mtrl-sci↗

arXiv2005

Effect of Coulomb interaction on the spin-galvanic mode in a two dimensional electron gas with Rashba spin-orbit interaction

Recently a new propagating mode of coupled charge and spin oscillations was predicted in a two dimensional electron gas with a sufficiently strong Rashba interaction. We show that Coulomb interactions qualitatively modifies the spectrum and increases the characteristic wavelength of this mode by orders of magnitude, but does not suppress it. An absorption experiment that can conclusively detect the presence or absence of such a propagating mode is proposed.

cond-mat.mtrl-sci↗

arXiv2005

Spin-reorientation in YbFeO_3

Precise measurements of YbFeO_3 magnetization in the spin-reoirentation temperature interval are performed. It is shown that ytterbium orthoferrite is well described by a recently developed modified mean field theory developed for ErFeO_3. This validates the conjecture about the essential influence of the rare earth ion's anisotropic paramagnetism on the magnetization behavior in the reorientation regions of all orthoferrites with Gamma{4} -> Gamma{24} -> Gamma{2} phase transitions.

cond-mat.mtrl-sci↗

arXiv2003

Magnetotransport near a quantum critical point in a simple metal

We use geometric considerations to study transport properties, such as the conductivity and Hall coefficient, near the onset of a nesting-driven spin density wave in a simple metal. In particular, motivated by recent experiments on vanadium-doped chromium, we study the variation of transport coefficients with the onset of magnetism within a mean-field treatment of a model that contains nearly nested electron and hole Fermi surfaces. We show that most transport coefficients display a leading dependence that is linear in the energy gap. The coefficient of the linear term, though, can be small. In particular, we find that the Hall conductivity $σ_{xy}$ is essentially unchanged, due to electron-hole compensation, as the system goes through the quantum critical point. This conclusion extends a similar observation we made earlier for the case of completely flat Fermi surfaces to the immediate vicinity of the quantum critical point where nesting is present but not perfect.

cond-mat.mtrl-sci↗

arXiv2003

Hall Effect in Nested Antiferromagnets Near the Quantum Critical Point

We investigate the behavior of the Hall coefficient in the case of antiferromagnetism driven by Fermi surface nesting, and find that the Hall coefficient should abruptly increase with the onset of magnetism, as recently observed in vanadium doped chromium. This effect is due to the sudden removal of flat portions of the Fermi surface upon magnetic ordering. Within this picture, the Hall coefficient should scale as the square of the residual resistivity divided by the impurity concentration, which is consistent with available data.

cond-mat.str-el↗

arXiv2000

Current Induced Magnetization Switching in Small Domains of Different Anisotropies

Several recent experimental studies have confirmed the possibility of switching the magnetization direction in the small magnetic domains by pumping large spin-polarized currents through them. On the basis of equations proposed by J.Slonczewski for the case when magnetization of the domains is almost uniform, we analyze the stability and switching for two types of magnetic and shape anisotropies of a magnetic domain in a nanowire and find qualitatively different behavior, including different shapes of bistable regions. Our study is analytic as opposed to recent numeric work. Assumed anisotropies can be realized in experiments and our predictions can be used to experimentally test the theory of spin-transfer torques. Such test would be especially interesting since alternative approaches are discussed in the literature.

cond-mat↗

arXiv1999

Stripe Formation within SO(5) Theory

We study the formation of stripe order within the SO(5) theory of high T_c superconductivity. We show that spin and charge modulations arise as a result of the competition between a local tendency to phase separate and the long-range Coulomb interaction. This frustrated phase separation leads to hole-rich and hole-poor regions which are respectively superconducting and antiferromagnetic. A rich variety of microstructures ranging from droplet and striped to inverted-droplet phases are stabilized, depending on the charge carrier concentration. We show that the SO(5) energy functional favors non-topological stripes.

cond-mat.supr-con↗

arXiv1997

Modification of the Landau-Lifshitz Equation in the Presence of a Spin-Polarized Current in CMR and GMR Materials

We derive a continuum equation for the magnetization of a conducting ferromagnet in the presence of a spin-polarized current. Current effects enter in the form of a topological term in the Landau-Lifshitz equation . In the stationary situation the problem maps onto the motion of a classical charged particle in the field of a magnetic monopole. The spatial dependence of the magnetization is calculated for a one-dimensional geometry and suggestions for experimental observation are made. We also consider time-dependent solutions and predict a spin-wave instability for large currents.

cond-mat.mtrl-sci↗

arXiv1994

Staggered Superconductivity in UPt$_3$: A New Phenomenological Approach

We present a new Ginzburg-Landau theory for superconductivity in UPt$_3$, based upon a multicomponent order parameter transforming under an irreducible space group representation; the phase is staggered in real space. Our model can explain the $H-T-P$ phase diagram including the tetracritical point for all field directions. We motivate this unconventional superconducting state in terms of odd-in-time-reversal pairing that may arise in one- or two-channel Kondo models, and suggest experimental tests.

cond-mat↗