Quasistatic magnetic permeability of an amorphous ferromagnet

Dependence of the differential magnetic permeability on the speed of magnetization reversal was found in ribbons of an amorphous ferromagnetic material. When the ribbon thickness is 10^–3 cm and the initial permeability is 10^–5, an increase in the frequency of the harmonic magnetization reversal causes a decrease of by a factor of 2–3; this takes place in the region around 100 Hz. The effect is explained by the influence of eddy currents on the magnetization distribution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 58–62, January, 1986.     

Classical spin-field model of a one-dimensional ferromagnet in an external magnetic field

The low temperature field dependent magnetization and susceptibility of the linear ferromagnet CsNiF₃ are compared with calculations for a one-dimensional classical spin field model.     

Vortex avalanches and magnetic flux fragmentation in superconductors

We report the results of numerical simulations of nonisothermal dendritic flux penetration in type-II superconductors. We propose a generic mechanism of dynamic branching of a propagating hot spot of a flux flow/normal state triggered by a local heat pulse. The branching occurs when the flux hot spot reflects from inhomogeneities or the boundary on which magnetization currents either vanish, or change direction. The hot spot then undergoes a cascade of successive splittings, giving rise to a dissipative dendritic-type flux structure. This dynamic state eventually cools down, turning into a frozen multifilamentary pattern of magnetization currents.     

Influence of magnetic scattering on superconductivity of ferromagnet/superconductor/ferromagnet spin-valve

Ferromagnet/superconductor/ferromagnet (F/S/F) spin-valve systems in the dirty limit, described by Usadel equations, was theoretically investigated with respect to superconducting transition temperature. Their superconducting characteristics strongly depend not only on the mutual orientation and thickness of the ferromagnetic layers, but also on the interface transparency as well as magnetic scattering. Especially, the introduction of magnetic scattering drastically reduces the spin-valve effect in our work. The obtained results could be used to understand experimental values of and to provide guidelines for optimizing the experimental systems.     

Propagation of avalanches in Mn12-acetate: magnetic deflagration

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.     

Effect of an AC magnetic field on the steady-state magnetization distribution in a weak ferromagnet

Possible steady-state magnetization distributions in a domain wall are found in a weak ferromagnet subjected to an ac magnetic field. The character of the rotation of the magnetization vector in the domain wall is determined. It is predicted that domain structures can be rearranged and reoriented under an ac magnetic field.     

Theory of the magnon-phonon interaction in magnetic field induced ferromagnet

The dependence of the elementary excitation energies and sound velocities on the magnetoelastic coupling and the magnetic field strength has been theoretically investigated in field-induced ferromagnets.It has been shown that near the field intensities, where the long range magnetic order appears, the acoustic quasi-phonon velocities and, in consequence, some elastic constants turn to zero. Such a behaviour has been interpreted as result of a structural phase transition.     

Response of spin-accumulated ferromagnet/superconductor/ferromagnet double tunnel junction to applied magnetic field

Tunneling current in a ferromagnet/superconductor/ferromagnet double tunnel junction induces a nonequilibrium spin accumulation in the superconductor. We study theoretically the response of such a system to applied magnetic field. We show that the interplay between the magnetic field and the spin accumulation could lead to novel bias voltage dependence and magnetic field dependence of the superconducting gap function, and bring in anomalous asymmetry in the spin-dependent transport. Our study also indicates a possible application of the spin injection.     

Ultrafast spin avalanches in crystals of nanomagnets in terms of magnetic detonation

Recent experiments [W. Decelle et al., Phys. Rev. Lett. 102, 027203 (2009)] have discovered ultrafast propagation of spin avalanches in crystals of nanomagnets, which is 3 orders of magnitude faster than the traditionally studied magnetic deflagration. The new regime has been hypothetically identified as magnetic detonation. Here we demonstrate unequivocally the possibility of magnetic detonation in the crystals, as a front consisting of a leading shock and a zone of Zeeman energy release. We study the key features of the process and find that the magnetic detonation speed only slightly exceeds the sound speed in agreement with the experimental observations. For combustion science, our results provide a unique physical example of extremely weak detonation.     

Solitons in an easy plane ferromagnet

Dynamical solitons in a uniaxial ferromagnet are considered. The second constant of magnetic anisotropy is taken into account. In the case of easy plane anisotropy the explicit form for the magnetization is found. The dispersion laws for obtained solitons are discussed.     

Local magnon modes and the dynamics of a small-radius two-dimensional magnetic soliton in an easy-axis ferromagnet

The internal dynamics of a small-radius precession magnetic soliton is considered. A variational formulation of the problem on the soliton-magnon interaction is proposed and used to calculate the frequency of a truly local mode. It is shown that this mode, as well as the conventional translational mode, remains localized in the small soliton radius limit. The presence of the local mode is confirmed by the numerical solution of the scattering problem.     

Elimination of magnetic relaxation in superconductors on approaching a ferromagnet

It is found that magnetic relaxation is suppressed in a high-temperature superconductor when it approaches a ferromagnet. It is supposed that this phenomenon results from formation of a nonequilibrium magnetic structure, in which counter driving forces act in different regions.     

Resistivity and magnetic measurements on the CePt ferromagnet

In this paper we present resistivity measurements performed on the CePt ferromagnet (T_c = 5.8 K) and on LaPt, together with magnetization measurements performed on CePt at low temperatures. The magnetic resistivity of CePt decreases as 1n(T) when temperature is increased above 220 K. This result associated with a reduction of the Ce magnetic moment and of the magnetic entropy at T_c suggests that CePt could be a Kondo system.     

Transition temperature of an Ising ferromagnet

By calculating the partition function over all one-break configurations the transition temperature of a one-dimensional Ising ferromagnet, with inverse-square interaction, is determined.     

Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers

We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La(2/3)Sr(1/3)MnO3/Pr(2/3)Ca(1/3)MnO3 (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0相似文献   

Double nuclear magnetic resonance in the weak ferromagnet YCrO3

Applications of 2D-NMR spectroscopy to measurements of the quadrupole splitting in magnetic materials are discussed using the weak ferromagnet YCrO₃ as a model system. A simple qualitative dissussion and results from computersimulations are given for various experiments. In systems with distributed electric field gradients the method provides a unique way to measure hyperfine field, quadrupole splitting and correlations between these local parameters.     

Observation of magnetic ripple and nanowidth domains in a layered ferromagnet

We investigated ferromagnetic domain structures on nanometer to micrometer scale for single crystals of a layered ferromagnet, La(2-2x)Sr(1+2x)Mn2O7 (0.32 < or = x < or = 0.40), as functions of x and temperature by means of Lorentz electron microscopy. We have succeeded in observing the evolution of magnetic ripple structure, dynamically, related to a spin reorientation transition where the magnetization direction switches between parallel and perpendicular to the layers. Our high-resolution magnetic domain imaging revealed that the ripple state is characterized by the evolution of magnetic nanowidth domains.     

Quantum spin model of a cubic ferromagnet in a magnetic field

The zero temperature phase diagram of a one-dimensional ferromagnet with cubic single ion anisotropy in an external magnetic field is studied. The mean-field approximation and the density-matrix renormalization group method are applied. Two phases at finite magnetic fields are identified: a canted phase with spontaneously broken symmetry and a phase with magnetization along the magnetic field. Both methods predict that the canted phase exists even for the single-ion anisotropy strong enough to destroy the magnetic order at zero magnetic field. In contrast to the mean-field theory, the density-matrix renormalization group predicts a reentrant behavior for the model. The character of the phase transition at finite magnetic field has also been considered and the critical index has been found. Received 9 May 2000 and Received in final form 5 July 2000