We study spin relaxation and dynamics of collective spin excitations in correlated double--exchange ferromagnets. For this, we introduce an expansion of the Green's functions equations of motion that treats non--perturbativerly all correlations between a given number of spin and charge excitations and becomes exact within a sub--space of states. Our method treats relaxation beyond Fermi's Golden Rule while recovering previous variational results for the spin--wave dispersion. We find that the momentum dependence of the spin--wave dephasing rate changes qualitatively due to the on--site Coulomb interaction, in a way that resembles experiment, and depends on its interplay with the magnetic exchange interaction and itinerant spin lifetime. We show that the collective spin relaxation and its dependence on the carrier concentration depends sensitively on three--body correlations between a spin excitation and a Fermi sea electron and hole. The above spin dynamics can be controlled via the itinerant carrier population.
We study spin transport between a ferromagnet with time-dependent magnetization and a conducting carbon nanotube or quantum wire, modeled as a Luttinger liquid. The precession of the magnetization vector of the ferromagnet due for instance to an outside applied magnetic field causes spin pumping into an adjacent conductor. Conversely, the spin injection causes increased magnetization damping in the ferromagnet. We find that, if the conductor adjacent to the ferromagnet is a Luttinger liquid, spin pumping/damping is suppressed by interactions, and the suppression has clear Luttinger liquid powe…
We analyze theoretically the novel pathway of ultrafast spin dynamics for ferromagnets with high enough single-ion anisotropy (non-Heisenberg ferromagnets). This longitudinal spin dynamics includes the coupled oscillations of the modulus of the magnetization together with the quadrupolar spin variables, which are expressed through quantum expectation values of operators bilinear on the spin components. Even for a simple single-element ferromagnet, such a dynamics can lead to an inertial magnetization reversal under the action of an ultrashort laser pulse.
The $S=1/2$ distorted diamond spin chain with the anisotropic ferromagnetic interaction is investigated using the numerical diagonalization and the level spectroscopy analysis. It is known that the system exhibits a plateau of the magnetization curve at the 1/3 of the saturation. The present study indicates that as the anisotropy is varied the quantum phase transition occurs between two different mechanisms of the 1/3 magnetization plateau. The phase diagram with respect to the anisotropy and the ferromagnetic coupling is also presented.
We develop a theory of the magnetization dynamics triggered by ultrafast optical excitation of ferromagnetic semiconductors. We describe the effects of the strong carrier spin relaxation on the nonlinear optical response by using the Lindblad semigroup method. We demonstrate magnetization control during femtosecond timescales via the interplay between circularly polarized optical excitation, hole-spin damping, polarization dephasing, and the Mn-hole spin interactions. Our results show a light-induced magnetization precession and relaxation for the duration of the optical pulse.
Interfacing a ferromagnet with a polarized ferroelectric gate generates a non-uniform, interfacial spin density coupled to the ferroelectric polarization allowing so for an electric field control of effective transversal field to magnetization. Here we study the dynamic magnetization switching behavior of such a multilayer system based on the Landau-Lifshitz-Baryakhtar equation, demonstrating that interfacial magnetoelectric coupling is utilizable as a highly localized and efficient tool for manipulating magnetism.
The magnetization-density distribution in the metallic ferromagnet SrRuO$_3$ was studied by means of polarized neutron diffraction. The analyzes by multipole refinements and by the maximum entropy method consistently reveal a strong polarization of all oxygen sites carrying 30\% of the total magnetization. The spin-density distribution on the Ru site exhibits a nearly cubic shape in agreement with an almost equal occupation of $t_{2g}$ orbitals and $pd$ hybridization. The experimental analysis is well reproduced by density functional calculations. There is no qualitative change in the magnetiz…
Thermodynamic properties of cubic Heisenberg ferromagnets with competing exchange interactions are considered near the frustration point where the coefficient $D$ in the spin-wave spectrum $E_{\mathbf{k}}\sim D k^{2}$ vanishes. Within the Dyson-Maleev formalism it is found that at low temperatures thermal fluctuations stabilize ferromagnetism by increasing the value of $D$. For not too strong frustration this leads to an unusual "concave" shape of the temperature dependence of magnetization, which is in agreement with experimental data on the europium chalcogenides. Anomalous temperature behav…
The weak itinerant ferromagnet UIr is studied by magnetization and magnetostriction measurements. Critical behavior, which surprisingly extends up to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is analyzed using Arrott and Maxwell relations. Critical exponents are found that do not match with any of the well-known universality classes. The low-temperature magnetization $M_s\simeq0.5$ $μ_B \cong const.$ below 3 T rises towards higher fields and converges asymptotically around 50 T with the magnetization at $T_C$. From the magnetostriction and magnetization data, we e…
The electrical and magnetic response to a bias current has been investigated in a singlecrystalline ferromagnetic manganese oxide $\Pr_{0.8}$Ca$_{0.2}$MnO$_3$ . A significant decrease of the magnetization is observed at the same threshold current where a non-linearity of V-I characteristics appears. Such a behavior cannot be understood in the framework of the filamentary picture usually invoked for the non linearity of the other manganese oxides. Instead, an analogy with spintronic features might be useful and experimental signatures seem to be in agreement with excitations of spin waves by an…
The temperature-dependence of the magnetization near the surface of a band-ferromagnet is measured with monolayer resolution. The simultaneous application of novel highly surface-sensitive techniques enables one to deduce the layer-dependent magnetization curves at a Fe(100) surface. Analysis of data is based on a simple mean-field approach. Implications for modern theories of itinerant-electron ferromagnetism are discussed.
We study the breakdown of the magnetization plateau at the magnetization M=M_{S}/3 (M_{S} is the saturation magnetization) of the S=1/2 anisotropic spin chain with ferromagnetic-ferromagnetic-antiferromagnetic interactions. We consider the model with the isotropic ferromagnetic (trimer) coupling J_{F}, and anisotropic antiferromagnetic coupling (J_{x}=J_{y}=J_{AF} and J_{z}=ΔJ_{AF}). For the limit of large γ\equiv J_{F}/J_{AF}, the model is equivalent to the S=3/2 XXZ chain with the exchange anisotropy Δ. There is a phase transition between the plateau (small-γ) and the no-plateau (large-γ) re…
We introduce a new approach to understand magnetization dynamics in ferromagnets based on the holographic realization of ferromagnets. A Landau-Lifshitz equation describing the magnetization dynamics is derived from a Yang-Mills equation in the dual gravitational theory, and temperature dependences of the spin-wave stiffness and spin transfer torque appearing in the holographic Landau-Lifshitz equation are investigated by the holographic approach. The results are consistent with the known properties of magnetization dynamics in ferromagnets with conduction electrons.
The low temperature magnetization process of the ferromagnetic-antiferromagnetic Heisenberg chain is studied using the interacting boson approximation. In the low field regime and near the saturation field, the spin wave excitations are approximated by the $δ$ function boson gas for which the Bethe ansatz solution is available. The finite temperature properties are calculated by solving the integral equation numerically. The comparison is made with Monte Carlo calculation and the limit of the applicability of the present approximation is discussed.
An analytical description of non-equilibrium phenomena in interacting quantum systems is rarely possible. Here we present one example where such a description can be achieved, namely the ferromagnetic Kondo model. In equilibrium, this model is tractable via perturbative renormalization-group techniques. We employ a recently developed extension of the flow-equation method to calculate the non-equilibrium decay of the local magnetization at zero temperature. The flow equations admit analytical solutions which become exact at short and long times, in the latter case revealing that the system alwa…
An approach to the electrostatic control of $90^{\circ}$ magnetization rotation in the hybrid structures composed of topological insulators (TIs) and adjacent ferromagnetic insulators (FMI) is proposed and studied. The concept is based on TI electron energy variation with in-plane to put-of plane FMI magnetization turn. The calculations explicitly expose the effect of free energy variability in the form of the electrically controlled uniaxial magnetic anisotropy, which depends on proximate exchange interaction and TI surface electron density. Combining with inherent anisotropy, the magnetizati…
The orbital magnetization and its effects on the two-dimensional kagomé lattice with spin anisotropies included in the general Hund's coupling region have been theoretically studied. The results show that the strength of the Hund's coupling, as well as the spin chirality, contributes to the orbital magnetization $\mathcal{M}$. Upon varying both these parameters, it is found that the two parts of $\mathcal{M}$, i.e., the conventional part $\mathbf{M}_{c}$ and the Berry-phase correction part $\mathbf{M}_Ω$, oppose each other. The anomalous Nernst conductivity is also calculated and a peak-valley…
The spin wave dispersion relation in both clean and disordered itinerant quantum ferromagnets is calculated. It is found that effects akin to weak-localization physics cause the frequency of the spin-waves to be a nonanalytic function of the magnetization m. For low frequencies Ω, small wavevectors k, and small m, the dispersion relation is found to be of the form Ω~ m^{1-α} k^2, with α= (4-d)/2 (2<d<4) for disordered systems, and α= (3-d) (1<d<3) for clean ones. In d=4 (disordered) and d=3 (clean), Ω~ m ln(1/m) k^2. Experiments to test these predictions are proposed.
Using the low-energy effective field theory for magnons, we systematically evaluate the partition function of the O(3) ferromagnet up to three loops. Dyson, in his pioneering microscopic analysis of the Heisenberg model, showed that the spin-wave interaction starts manifesting itself in the low-temperature expansion of the spontaneous magnetization of an ideal ferromagnet only at order $T^4$. Although several authors tried to go beyond Dyson's result, to the best of our knowledge, a fully systematic and rigorous investigation of higher order terms induced by the spin-wave interaction, has neve…
