Magnetism in disordered magnetic Fe82−xNixCr18

The zero field μSR-method has been used to study the magnetism in the disordered magnetic alloy Fe_82−xNi_xCr₁₈ near the three-critical, pointx=25. The dynamic and static local field distributions are analyzed. The difference between spin-glass states obtained either from the paramagnetic or after the double transition is discussed.     

Study of the heavy-fermion compound CeRu<Subscript>2</Subscript>Si<Subscript>2</Subscript> by the small-angle neutron scattering method

In order to directly observe neutron scattering by heavy fermion quasiparticles at low temperatures, a CeRu₂Si₂ single crystal has been studied by the small-angle neutron scattering method. In the experiment, neutron scattering is observed at T = 0.85 K for momentum transfers q ≤ 0.04 Å^?1, which is treated as the orbital component of magnetic scattering by heavy fermion quasiparticles. It has been found that the application of a magnetic field H = 1 T leads to both an increase in the observed scattering and its anisotropy with respect to the field direction. Moreover, measurements in the magnetic field reveal additional scattering for q > 0.04 Å^?1, which is well described by a Lorentzian and is interpreted as neutron magnetic scattering by spin-density fluctuations with a correlation radius R_c ≈ 30 Å.     

The asymmetric effects for polarized neutron scattering from ferromagnets above the Curie point in magnetic field

The polarized neutron scattering from ferromagnets in magnetic field above the Curie point is considered. Some new effects are discussed. It is shown that experimental investigation of these effects may be used for: 1) the verification of Polyakov-Kadanoff algebra predictions, 2) making a choice between two variants of critical dynamics of ferromagnets in dipolar region, 3) the investigation of three-point dynamical spin correlations.     

RKKY interaction in layered superconductors with anisotropic pairing

The RKKY interaction between localized moments in layered d-wave superconductors is considered at T ? T _c . It is shown that the interaction is anisotropic and consists of two terms: conventional oscillating one and the positive term, which is proportional to the gap function and decreases in the 2D case inversely proportional to the distance. Both of these terms reveal crossover to the more rapid decay law at large distances, exponential one away from the nodal directions of order parameter and power-like law close to them. If the background in the normal state is ferromagnetic, d-wave superconductivity results in helicoid ordering with a star of helicoid axes fixed by nodes. The period of this skew structure has unconventional ξ^1/2 dependence on the correlation length.     

Quantum frustrations in quasi-2D antiferromagnets

An influence of localized holes on magnetic properties of the CuO₂ planes in quasi-2D antiferromagnets (La₂CuO₄, YBa₂Cu₃O_+x etc.) is studied. It is demonstrated that the hole localized on the bond connecting Cu²⁺ ions gives birth to frustration which in a wide range of parameters behaves as the two-level system with the energyEJ, whereJ is the exchange interaction of the neighbouring copper spins. As a result forTE the spin-wave energy may noticeably decrease even at a low concentration of the holesc if the parametercJ|E| is not small. When this parameter is greater than unity, the reentrant transition may occur in the system. Experimental data presently available are in a qualitative agreement with the theoretical predictions.     

Additional raising of the degeneracy of CEF-split Ho3+ ions by antiferromagnetic spin-waves in Ho0.1Y0.9Ba2Cu3O6.13

Inelastic neutron scattering has been employed to study in detail the low-energy crystal-field (CEF) excitations of Ho³⁺ in tetragonal antiferromagnetic (AF) Ho_0.1Y_0.9Ba₂Cu₃O_6.13. We observe a splitting of the lowest excited ₅ doublet atT=1.5 K. This splitting is explained as resulting from the exchange interaction with the AF subsystem of copper spins. The corresponding susceptibility at the Ho³⁺ site has a symmetry lower than the tetragonal one of the CEF potential and, as a result, produces the splitting. The value of the coupling between Ho³⁺ and Cu²⁺ ionsJ _ex=2.4 meV is derived from the experimentally observed value of the splitting E=0.1 meV and parameters of the AF subsystem, known from the neutron scattering experiments. Some possible consequences of the rare-earth (RE)-copper exchange are discussed, including the interaction between RE ions via the virtual exchange by spin waves.     

On the paramagnetic resonance and the longitudinal relaxation of ferromagnets in the critical region above Tc

Uniform dynamical susceptibility of cubic ferromagnets above T_c in magnetic field is investigated. Resonance frequences and damping constants are determined in the limiting cases of low and strong magnetic field. It is shown that in the exchange temperature region when 4πχ ? 1 owing to spin diffusion the uniform susceptibility is depended non-trivially on the frequency and the magnetic field. From this dependence the temperature behaviour of spin diffusion coefficient can be determined.     

Tunneling states in amorphous ferromagnets

A model of an amorphous ferromagnet in which a certain number of atoms forms two-level systems is considered. Relaxation time of such systems due to the interaction with spin waves is calculated and it is shown that this time can be comparable to the phonon relaxation time. The spin wave damping in such ferromagnet is determined and the magnetic contribution to the thermal conductivity is calculated.