Magnetic Moment Oscillations Research Articles

Теория кристаллических полей и спектров возбуждения в Fe-=SUB=-2-=/SUB=-Mo-=SUB=-3-=/SUB=-O-=SUB=-8-=/SUB=-

The parameters of even and odd crystal fields acting on iron ions in tetrahedral and octahedral positions of the Fe2Mo3O8 crystal are calculated. The obtained energy level schemes of the lowest multiplets are discussed in the context of the available experimental data. By comparing the calculated intensities of magnetic and electric dipole transitions with experimental data, the parameters of the effective Hamiltonian of the interaction of 3d electrons with an electric field are refined. It is found that the main absorption lines at T < TN in the region of terahertz frequencies are due to excitations of iron ions and are not associated with collective oscillations of magnetic moments. The splitting of absorption lines upon application of an external magnetic field is a consequence of the difference in the orientations of the magnetic sublattices relative to the crystallographic axes.

Photovoltage detection of spin excitation of a ferromagnetic stripe and disk at low temperature

Photovoltage spectroscopy is a beneficial technique to investigate the dynamic properties of the spin excitations of ferromagnetic elements fabricated at the surface of a GaAs/Al0.33Ga0.67As heterojunction. This method is of particular interest for probing localized spin wave modes. The high sensitivity of the photovoltage technique arises from the high electron mobility of 2D electrons μ = 1.5 × 106 cm2 · V−1 · S−1 which enables efficient rectification of magnetic moment oscillations through the Hall effect. We report on the discrete structure of spin wave eigenmodes as a function of magnetic field orientation, the shape of Co ferromagnets, and the geometry of nanomagnets. We indicated bonding–antibonding spin waves when the static magnetic field, is parallel to the short side of the stripe at different microwave frequencies at 4 K. We also observed Damon–Eshbach modes when is parallel to the stripe. Micromagnetic simulations confirm the experimental results. We observe the discrete structure of the photovoltage for individual dots. We also investigate the effect of the magnetocrystalline anisotropy field of Co on ferromagnetic resonance. Our results demonstrate that photovoltage measurements in hybrid semiconductor-ferromagnetic structures provide a sensitive and extended tool for probing the spin waves of small magnets with a size of 80 nm.

The magnetoelectric MEE-effect in the SmFe3(BO3)4 multiferroic in dc and ac electric fields

The inverse magnetoelectric MEE-effect in the SmFe3(BO3)4 single-crystal sample in an applied electric field has been studied. The electric field E consists of two components: a constant one, e0, and a variable one, e × cos(ωt). The investigated compound evokes great interest due to the existence of both linear and quadratic contributions to the magnetoelectric effect. According to theoretical analysis, the effective susceptibility of the first harmonic of magnetic moment oscillations depends on the dc electric field component e0. Indeed, according to the measurement data, the dc field e0 significantly affects the MEE-effect first-harmonic amplitude: depending on the e0 sign, these oscillations can be either amplified or suppressed. This offers an opportunity for controlling the magnetic moment oscillation amplitude at the applied electric field frequency, including the signal modulation, which is promising for application. In the applied dc field e0, a slight change in the susceptibility of the MEE-effect term quadratic to the electric field was detected. The mathematical apparatus used correctly describes the qualitative dependence of the MEE-effect amplitude on the dc field e0, while the quantity appears to be approximately twofold overestimated.

Отклик решетки магнитных наночастиц на импульс магнитного поля вблизи границы устойчивости

AbstractThe dynamic response of a system being near the stable equilibrium boundary to an external magnetic field pulse is studied for 2D lattices of magnetic nanoparticles with cubic crystallographic anisotropy. The conditions under which magnetic moment oscillations from individual dipoles propagate to the entire system are revealed. This effect results in the lattice response are significantly larger in the external pulse duration and with an amplitude rather weakly depending on initial conditions and external field parameters, the processes during which the pulse results in reorientation of only individual lattice dipoles.

Response of a magnetic nanoparticle lattice to a magnetic field pulse near the stability boundary

The dynamic response of a system being near the stable equilibrium boundary to an external magnetic field pulse is studied for 2D lattices of magnetic nanoparticles with cubic crystallographic anisotropy. The conditions under which magnetic moment oscillations from individual dipoles propagate to the entire system are revealed. This effect results in the lattice response are significantly larger in the external pulse duration and with an amplitude rather weakly depending on initial conditions and external field parameters, the processes during which the pulse results in reorientation of only individual lattice dipoles.

Excitation of the orientation transition wave and chaotic dynamics in a lattice of magnetic nanoparticles

The propagation of the front of oscillatory dynamics of magnetic moments caused by the local perturbation of the lattice along a system is studied for planar three-row lattices of magnetic nanoparticles having cubic anisotropy and coupled by the dipole interaction. The propagation of both the transition between two equilibrium planar configurations and chaotic oscillations of magnetic moments in the case of their initial orientation perpendicular to the plane of the lattice is implemented. The possibility of controlling the velocity of propagation of the orientation transition wave and its stop is revealed. The appearance of the moving front of the chaotic dynamics is found at switching on and switching off the local external field and at the action of the alternating field pulse.

Antiferromagnetic interlayer coupling and thus induced distinct spin texture for the [LaMnO3/LaCoO3]5 superlattices.

Artificial engineering of an interfacial spin structure of complex oxides with strongly coupled spin, orbital, charge and lattice degrees of freedom is crucially important for the exploration of novel effects associated with magnetic tunneling, exchange biasing, and spin injecting/manipulating, which are the central issues of spintronics. Here we demonstrate the presence of a distinct interlayer coupling between LaMnO3 (LMO) and LaCoO3 (LCO) and the resulting dramatic effect on the spin structure. We found that the LCO layer in (LMO/LCO)5 superlattices exhibits not only an antiferromagnetic coupling with a neighboring LMO layer but also a long-range magnetic order with substantially reduced magnetization. As suggested by density functional theory calculations, interlayer coupling can induce a spatial oscillation of magnetic moment within the LCO layer, resulting in low magnetization.

Regimes of Magnetic Moment Oscillations in Domain Wall of the Dipole Chain

We report the dynamics of the magnetic moment numerically simulated for a single chain of magnetic nanodots affected by an external static or alternating field applied to the domain wall. It is shown that for a weak exchange interaction, the oscillations of the magnetic moment transverse components are a sequence of trains, while for a strong interaction, the dynamics approaches to a single-frequency harmonic oscillation. The amplitude and the frequency of these oscillations are determined by the energy of an interaction between the chain elements and by the external field, respectively. Various oscillation regimes induced by an external alternating field are studied. The effect of an easy-plane and easy-axis uniaxial anisotropy on the system dynamics is demonstrated.

Extinction of Magnetostatic Modes in Ferrospinel Films

Absorption spectra of ferrospinel films synthesized by the method of chemical transport reactions are considered. Using an EPR spectrometer, it is demonstrated that additional absorption peaks are recorded in the absorption spectra of manganese and magnesium-manganese ferrite films magnetized parallel to their surface. Interpreting these peaks as magnetostatic modes, the wave number, group velocity, and extinction coefficient are retrieved from experimental values of the saturation magnetization, crystallographic anisotropy constant, and magnetic field of the observed modes. The common effects typical of the ferrospinel films are frequency oscillations of the surface mode extinction. Dependences of the extinction oscillation pattern on the surface anisotropy and wavelength of magnetic moment oscillations are established.

Магнитостатические моды в касательно намагниченных плeнках феррошпинелей

Absorption spectra of ferrospinel films synthesized by the method of chemical transport reactions are considered. Using an EPR spectrometer, it is demonstrated that additional absorption peaks are recorded in the absorption spectra of manganese and magnesium-manganese ferrite films magnetized parallel to their surface. Interpreting these peaks as magnetostatic modes, the wave number, group velocity, and extinction coefficient are retrieved from experimental values of the saturation magnetization, crystallographic anisotropy constant, and magnetic field of the observed modes. The common effects typical of the ferrospinel films are frequency oscillations of the surface mode extinction. Dependences of the extinction oscillation pattern on the surface anisotropy and wavelength of magnetic moment oscillations are established.

Interfacial electronic structure and magnetoelectric effect in M/BaTiO3 (M=Ni, Fe) superlattices

Using first-principles density functional theory, we investigate the interfacial electronic structure and magnetoelectric effect in M/BaTiO3 (M=Ni, Fe) superlattices, and find a novel type of interfacial magnetoelectric coupling mechanism in the Ni/BaTiO3 interface. This magnetoelectric effect is determined by the change of magnetic moments on Ni atoms near the interface, instead of the induced moments on interfacial Ti atoms in Fe/BaTiO3 system, which is also distinguished from the spin-polarized carriers screening mechanism. The underlying physics is the strong interface bonding and the pdσ-type magnetic interactions between Ni 3d and O 2p spins. Furthermore, there exists an extraordinary intralayer oscillation of magnetic moments within the Ni layers, which may be observed in experiments.

Measuring spectrum of spin wave using vortex dynamics

We propose to measure the spectrum of magnetic excitation in magnetic materials using the motion of a vortex lattice driven by both ac and dc currents in superconductors. When the motion of a vortex lattice is resonant with the oscillation of magnetic moments, the voltage decreases at a given current. From transport measurement, one can obtain the frequency of the magnetic excitation with the wave number determined by the vortex-lattice constant. By changing the lattice constant through applied magnetic fields, one can obtain the spectrum of the magnetic excitation up to a wave vector of order $10\phantom{\rule{4pt}{0ex}}{\mathrm{nm}}^{\ensuremath{-}1}$.

Oscillation of the magnetic moment in modulated martensites in Ni2MnGa studied by ab initio calculations

We have revealed the oscillations in the distribution of the magnetic moments in modulated martensites in Ni2MnGa ferromagnetic shape memory alloy, by first-principles density-functional calculations. It is demonstrated that the oscillation of Ni magnetic moment that depends on the atomic shuffling in the superstructure dominates the distribution of the total magnetic moment per Ni2MnGa unit. The structure change-associated total magnetic moment has been found to increase for Ni2MnGa unit from the cubic austenite to the tetragonal nonmodulated (NM) martensite through the monoclinic modulated martensites.

Resonant excitation of single-pulse nuclear spin echo in magnetically ordered media

An analytical expression for a single-pulse nuclear echo signal in magnetically ordered materials has been obtained taking into account inhomogeneous broadening of the spectroscopic transition and non-uniform distribution of the enhancement factor. The signal has been shown to result from superimposing the nuclear magnetic moment oscillations of the same amplitude and phase that arise upon termination of a radio-frequency pulse. The cause for the effective suppression of oscillations of nuclear magnetic moments in the initial phase of the free precession signal has been determined analytically. The single-pulse echo signal amplitude has been found as a function of the external variable magnetic field strength, the exciting pulse duration, the inhomogeneous NMR line broadening, and the distribution width of the enhancement factor. The results have been compared with experimental data observed in a Co2MnSi ferromagnetic polycrystalline sample.

Magnetic moment oscillation in ammonium perchlorate in a DC SQUID-based magnetic resonance experiment

In this work we describe experimental results in which a DC SQUID (superconducting quantum interference device) is used as free induction decay detector. Measurements of a solid ammonium perchlorate (NH 4ClO 4) sample were performed, in zero field, at 4.2 K. Unexpected magnetic moment oscillations were detected at 1.5 kHz. The computation of the magnetic fields suggests that the proton nuclear magnetic resonance may explain the measured resonance, considering reorientation of the ammonium group by quantum tunneling of protons and a magnetic proton dipole–dipole intermolecular interaction model.

Superconductivity in Pb inverse opal

Type-II superconducting behavior was observed in highly periodic three-dimensional lead inverse opal prepared by infiltration of melted Pb in blue ( D = 160 nm), green ( D = 220 nm) and red ( D = 300 nm) opals and followed by the extraction of the SiO 2 spheres by chemical etching. The onset of a broad phase transition (Δ T = 0.3 K) was shifted from T c = 7.196 K for bulk Pb to T c = 7.325 K. The upper critical field H c2 (3150 Oe) measured from high-field hysteresis loops exceeds the critical field for bulk lead (803 Oe) fourfold. Two well resolved peaks observed in the hysteresis loops were ascribed to flux penetration into the cylindrical void space that can be found in inverse opal structure and into the periodic structure of Pb nanoparticles. The red inverse opal shows pronounced oscillations of magnetic moment in the mixed state at low temperatures, T < 5.5 K. The shape of these oscillations and their temperature dependence indicate on phase transitions in the fluxoid state of Pb core. The weak matching effect in the field dependence of magneto-resistivity measurement at low magnetic fields and T > 0.9 T c has been observed for all of the samples studied. The magnetic field periodicity of resistivity modulation is in good agreement with the lattice parameter of the inverse opal structure. We attribute the failure to observe pronounced modulation in magneto-resistive measurement to difficulties in the precision orientation of the sample along the magnetic field.

Ni 단층이 삽입된 Rh 박막의 전자구조와 자성

A single slab in which one Ni(001) atom layer embedded between two of four Rh layers is considered to examine the oscillation of magnetic moment in each layer. The all electron total-energy full-potential linearized augmented plane wave(FLAPW) method was used to calculate the spin densities, magnetic moments, density of states(DOS), and the number of electrons within each muffin-tin(MT) sphere. The magnetic moment of the center layer Ni(C) in the system of 4Rh/Ni/4Rh is calculated to be 0.34, which is 40% have magnetic moment at the interface layers by strong band hybridization with Ni(C) when Ni(001) monolayers is inserted, and the magnetic moment shows a damped oscillation as we go from center Ni(C) layer to the surface Rh(S). From the calculated density of states, it is found that the Fermi level shifts inside the energy band of the Ni(C) in affection of Rh(001).

Single-Pulse Nuclear Echo Signals in Magnetically Ordered Media

An analytical expression for the amplitude of a single-pulse nuclear echo signal generated in magnetically ordered materials is obtained taking into account the inhomogeneous broadening of the spectroscopic transition and the inhomogeneous distribution of the gain with an average value of greater than unity. It is shown that, in this signal, summation of the oscillations of nuclear magnetic moments with equal amplitudes and phases occurs at each instant of time. The cause of the effective suppression of the nuclear magnetic moment oscillations in the initial portion of the free precession signal is revealed analytically. The dependence of the amplitude of the one-pulse echo signal on the strength of an external alternating magnetic field, the pulse duration, and the width of the gain distribution is determined. The results obtained are compared with the experimental data for a Co2MnSi ferromagnetic polycrystalline sample.

Fast oscillations in (TMTSF) 2X

We report on the temperature dependence of the “fast oscillation” phenomenon in quasi-one dimensional molecular conductors. Magnetoresistance and magnetization measurements to 30T in the ambient pressure spin density wave state have been taken for the X = NO 3, PF 6 and AsF 6 members of the (TMTSF) 2X family. Complementary data on X=AsF 6 are presented by Ulmet et al. in these proceedings. All three compounds exhibit a peak in the transverse magnetoresistances ρ xx (B//c *, I//a) and ρ yy (B//c *, I//b) and thenoscillatory components around 3K, with the oscillations vanishing at higher and lower temperatures. No magnetic moment oscillations are detected in PF 6 or AsF 6, while only extremely weak oscillations (δm~10 −10 emu) are seen in the NO 3 salt above 25T. Also, no oscillations were observed in longitudinal magnetoresistance ρ zz (B//I//c *) measurements performed on AsF 6 and PF 6. Possible scenarios which have been used to explain the data include imperfect nesting at T SDW leaving behind quantizable closed orbits, and quantum interference effects arising from magnetic breakdown orbits. Another may involve a new phase transition inside the SDW state.

Oscillations of magnetic moment in layered superconductors

We show theoretically that strong magnetic pinning in superconductor-normal metal superlattices in the presence of a parallel magnetic field causes a nonmonotonic, oscillatory field dependence of the magnetic moment.