Possibility of observing chiral-symmetry effects in ferromagnetic nanoparticles

The statistics of left-and right-handed vortical magnetization states in a system of submicron-sized ferromagnetic disks is studied experimentally. Lattices of elliptic cobalt particles with a planar size of 750 × 450 nm and a thickness of 25 nm were formed using high-resolution electronic lithography. To visualize the magnetization distributions in the disks, magnetic force microscopy was used. The experimental results indicate the conservation of magnetic chiral symmetry in cobalt ferromagnetic particles of the above size and shape.     

Properties of Josephson junctions in the inhomogeneous magnetic field of a system of ferromagnetic particles

The effect of an array of ferromagnetic nanoparticles on the field-dependent critical current of the short overlap Josephson junction is experimentally studied. Large reversible variations of the maximum critical current are observed depending on the magnetic state of the particles. The pronounced commensurability effects are detected which are proved by the additional peaks of magnetic field induced diffraction pattern.     

Nonreciprocal cell for neutrons

The effect of nonreciprocal transmission of thermal neutrons (λ = 3–6 Å) through a system of magnetic mirrors with a noncoplanar distribution of the magnetic induction is predicted and observed experimentally. The relative difference between the transmittances for the direct and inverse processes reaches 75%. Thereby, the feasibility of a nonreciprocal cell for spin-1/2 particles is demonstrated.     

Tunnel magnetoresistance of bilayer ferromagnetic nanoparticles with magnetostatic interlayer interaction

A new method for forming submicron magnetic tunnel junctions consisting of two CoFe ferromagnetic layers separated by a dielectric TaO _x spacer is proposed. It is shown that the tunnel magnetoresistance effect can be used for studying the features of magnetization reversal of bilayer ferromagnetic nanoparticles.     

Exchange Enhancement of the Magnetocaloric Effect in Ferromagnetic Nanostructures (Brief Review)

JETP Letters - An approach to magnetic cooling based on the proximity effect of ferromagnets with different Curie temperatures is proposed. An analogy is drawn between the magnetotransport...     

Localized superconductivity in superconductor-ferromagnet hybrid structures

The results of theoretical and experimental investigations of the peculiarities of the nucleation of superconductivity in the presence of a nonuniform magnetic field induced by ferromagnetic films or dots with out-of-plane magnetic anisotropy are reviewed. It is shown that the phase transition line of superconductor-ferromagnet hybrids in the H-T plane (H is an external magnetic field and T is temperature) is determined significantly by the spatial distribution of nonuniform magnetic field. It allows to control the thermodynamic and transport properties of superconductor-ferromagnet hybrids by tuning the magnetic state of the ferromagnet.     

Interference amplification of the magneto-optic Kerr effect in multilayer structures in the X-ray range

The problem of X-ray reflection from multilayer structures with magnetic layers has been solved. The matrix for reflection of electromagnetic waves from such structures has been calculated analytically in kinematical and dynamical approximations. It is shown that not only reflection coefficients, but also magneto-optic effects are enhanced near Bragg peak. The possibility of measuring magneto-optic effects in multilayer structures without using synchrotron radiation has been estimated.     

Analysis of cross-correlation of interface roughness in multilayer structures with ultrashort periods

The diffusion scattering method is used for studying a series of W/B₄C multilayer structures with ultrashort periods (d = 0.8–1.5 nm). A simple theoretical model is described; the model takes into account both the dynamic effects in the interaction of counter-propagating diffuse-scattered waves and the mixing of film materials at the boundaries of the layers. It is shown that multilayer structures with a number of bilayers up to N = 700 and values of periods up to 0.8 nm are multilayer structures, which are well-correlated along the boundaries and exhibit resonance diffuse scattering. For structures with a period d > 1.1 nm, the largest contribution to the imperfection of boundaries comes not from the roughness, but from mixing of the films. The range of minimal periods of multilayer structures, for which the continuity of the films is preserved, is determined. The effect of “smoothing” of the substrate surface is discovered in multilayer structures with intact continuity; this contradicts to a certain extent the assumption concerning complete longitudinal correlation of roughnesses, which forms the basis of the theory.     

Collective effects accompanying magnetization of two-dimensional lattices of nanosize magnetic particles

Collective effects arising in a two-dimensional lattice of nanosize magnetic particles as a result of the dipole interparticle interaction are investigated by Hall magnetometry. The experimental system consists of 10⁵ permalloy particles having a diameter of ∼40 nm and a height of ∼40 nm and forming a lattice with a rectangular unit cell (90 nm×180 nm). We attribute the characteristic features observed in the magnetization curves to quasi-one-dimensionality of the experimental lattice of particles and to the formation of solitons in chains of dipoles. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 475–479 (25 September 1998)     

Phase transitions in a two-dimensional dipole ferrimagnet

The magnetic configurations of the system of magnetic dipoles that have different values and are arranged in a staggered order on a square lattice are studied. A numerical simulation is used to study the phase transitions in the system when the mismatch between the dipoles changes. The restructuring of the magnetic configuration of the system induced by a change in the mismatch is shown to proceed via sequential second-order phase transitions between collinear and noncollinear phases. The numerical simulation results are supported by analytical calculations performed with trial functions.