The spin-spin relaxation rate of paramagnetic impurities in antiferromagnets

The interaction between paramagnetic impurities in easy plane type antiferromagnets at finite temperatures is considered. In the framework of the diagram spin-operator technique the spin-spin relaxation rate Γ of paramagnetic impurities is investigated. It is shown that Γ depends strongly on the location of a local mode frequency in a spin wave band and on the impurity concentration. In the high temperature region Γ does not depend on temperature in the range c《c¹ while in the range c?c¹Γ is temperature dependent: $\text{Γ～?}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$.     

The nuclear spin interaction with paramagnetic impurities in antiferromagnets

The influence of paramagnetic impurities on the relaxation frequencies of the nuclear subsystem in antiferromagnets is investigated. In the framework of the spin operator diagram technique the nuclear spin-spin as well as spin-lattice relaxation rates are calculated. The correlation effects due to indirect spin-spin interaction via magnons both in nuclear and impurity subsystems are taken into account.     

The influence of magnetic impurities in the vortex core dynamics in magnetic nano-disks

In this work we have used spin dynamics simulations to study the gyrotropic frequency behavior in nano-disks of Permalloy with magnetic impurities. We consider the effect of attractive impurity and repulsive impurity placed near the vortex core gyrotropic trajectory. We observed that the gyrotropic frequency is affected by the presence of impurity. The gyrotropic frequency shift depends on the relative position between the impurity and the vortex core gyrotropic trajectory and if impurity is attractive or repulsive. Our results agree with the analytical model and with experimental behavior for the gyrotropic frequency shown in the literature.     

Universal alternating order around impurities in antiferromagnets

The study of impurities in antiferromagnets is of considerable interest in condensed matter physics. In this Letter we address the elementary question of the effect of vacancies on the orientation of the surrounding magnetic moments in an antiferromagnet. In the presence of a magnetic field, alternating magnetic moments are induced, which can be described by a universal expression that is valid in any ordered antiferromagnet and turns out to be independent of temperature over a large range. The universality is not destroyed by quantum fluctuations, which is demonstrated by quantum Monte Carlo simulations of the two-dimensional Heisenberg antiferromagnet. Physical predictions for finite doping are made, which are relevant for experiments probing Knight shifts and the order parameter.     

The magnetic order of two-dimensional anisotropic antiferromagnets

We study the two-dimensional quantum Heisenberg antiferromagnet on the square lattice with easy-axis exchange anisotropy by means of Green’s function approach within random phase and Callen’s approximations. The Néel temperature T_N, energy gap w₀ and staggered magnetization m are calculated. The theoretical predictions of T_N and w₀ for K₂NiF₄, Rb₂MnF₄, K₂MnF₄, Rb₂MnCl₄ and (CH₃NH₃)₂MnCl₄ fit well to the measured values. The power law behavior of is also investigated. The exponents β and ν for K₂NiF₄ are in excellent agreement with the experimental results.     

Surface magnetic polaritons on uniaxial antiferromagnets

The dispersion relation of surface polaritons for a uniaxial antiferromagnet are calculated taking account of retardation. In the presence of an external magnetic field, one finds that inequivalent propagation occurs in the Voigt configuration (±n? × H₀). For a high frequency permeability smaller than a critical value, the surface polaritons in the ?n? × H₀ direction, where n? is the normal to the interface, merges in the same frequency domain as the bulk polaritons.     

Macroscopic magnetic fields of antiferromagnets

The macroscopic magnetic fields arising in the space outside or in the bulk of an antiferromagnet in the absence of external currents are a result of surface magnetization. The general problem of determining these fields is formulated. It is shown that the field distribution near special lines on the surface is monopolar. An experimental study of the field makes it possible to determine the surface magnetization on the faces of an antiferromagnetic crystal. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 724–728 (10 May 1996)     

Imaging bond order near nonmagnetic impurities in square-lattice antiferromagnets

We study the textures of generalized "charge densities" (scalar objects invariant under time reversal), in the vicinity of nonmagnetic impurities in square-lattice quantum antiferromagnets, by order parameter field theories. Our central finding is the structure of the vortex in the generalized density wave order parameter centered at the nonmagnetic impurity. Using exact numerical data from quantum Monte Carlo simulations on an antiferromagnetic spin model, we are able to verify the results of our field theoretic study. We extend our phenomenological approach to the period-4 bond-centered density wave found in the underdoped cuprates.     

Theory of itinerant antiferromagnets in magnetic fields

In this contribution, we develop a theory of an itinerant antiferromagnet, which is a generalization of previous theories by taking into account more general band structures and homogeneous magnetic fields. As a result we obtain several phase transitions at finite magnetic fields, and also other thermodynamic properties are changed compared with these previous theories.     

Effects of heavy impurities on thermodynamic properties of solid hydrogen

The influence of a heavy substitutional impurity on the thermodynamics of the rotational sub-system of solid hydrogen is studied. A splitting of 3°K is found for the rotational level of the orthohydrogen molecule with the heavy impurity as the nearest neighbour on the assumption that the heavy isotopic impurity suppresses short-range dynamic correlations. The contribution of impurity-orthomolecule pairs to the thermodynamics of the rotational sub-system is also studied. The calculated values are in a fair agreement with experiment.     

The magnetic properties of three-dimensional spin-1 easy-axis single-ion anisotropic antiferromagnets

The ordered and disordered phases of spin-1 Heisenberg and Ising antiferromagnets with easy-axis single-ion anisotropy on a three-dimensional lattice are studied. By using of the double-time Green’s function method within the Tyablikov decoupling for the exchange anisotropy and Callen’s approximation for the single-ion anisotropy, the Néel temperature, magnetization and susceptibility are investigated. Their relations with the temperature and anisotropic parameter are analyzed over the entire range of temperature. It is found that our results agree well with spin wave theory results at low temperature, agree with the high temperature series results at high temperature, and compare reasonably well with the linked-cluster series approach and ratio method results at intermediate temperature.     

Scaling of the magnetic response in doped antiferromagnets

A theory of the anomalous omega/T scaling of the dynamic magnetic response in cuprates at low doping is presented. It is based on the memory function representation of the dynamical spin susceptibility in a doped antiferromagnet where the damping of the collective mode is constant and large, whereas the equal-time spin correlations saturate at low T. Exact diagonalization results within the t-J model are shown to support assumptions. Consequences, for both the scaling function and the normalization amplitude, are well in agreement with neutron scattering results.     

The influence of a radial magnetic field on current-voltage characteristics of toroidal glow discharge

The present paper deals with the influence of a radial magnetic field on different regions of the toroidal glow discharge and with the subsequent changes of the current-voltage characteristics. From the above it is clear that when studying the influence of a transverse magnetic field on the glow discharge it is necessary to understand that the discharge is not a homogeneous unit and the change of current-voltage characteristics involves the total sum of changes of the properties in different regions of the discharge.     

The de Haas-van Alphen effect and magnetic impurities

The de Haas-van Alphen (dHvA) effect in alloys containing magnetic impurities is a good tool to investigate the Kondo effect. We discuss first differences between the dHvA experiment for magnetic impurities and for nonmagnetic impurities. Then a review is made on the extent to which experimental data can be interpreted theoretically. The main part is devoted to theoretical analysis of Cu-based alloys, for which systematic data are available.     

Anomalous curie response of impurities in quantum-critical spin-1/2 Heisenberg antiferromagnets

We consider a magnetic impurity in two different S=1/2 Heisenberg bilayer antiferromagnets at their respective critical interlayer couplings separating Néel and disordered ground states. We calculate the impurity susceptibility using a quantum Monte Carlo method. With intralayer couplings in only one of the layers (Kondo lattice), we observe an anomalous Curie constant C*, as predicted on the basis of field-theoretical work [S. Sachdev, Science 286, 2479 (1999)10.1126/science.286.5449.2479]. The value C* = 0.262 +/- 0.002 is larger than the normal Curie constant C=S(S+1)/3. Our low-temperature results for a symmetric bilayer are consistent with a universal C*.     

Dynamics of antiferromagnets exposed to ultrashort magnetic field pulses

An ultrashort magnetic field pulse generated by a laser pulse can excite spin oscillations in a “pure” antiferromagnet even when a weak ferromagnetic moment is absent. This mechanism features the spin oscillation amplitude independent of the sublattice structure and parameters of the ferromagnet and is governed only by the field pulse parameters.     

Multichanel localization and magnetic impurities

The behaviour of an electron in N-coupled conducting chains of the length L is studied in the presence of magnetic impurities. The electron flow can be expanded in an orthonormal set of 2N channels. Each channel has its own transmission coefficient T_n(L). Spontaneous breaking of the symmetry between channels results in 2N different exponential dependences T_n(L) ～ exp (—L/l¹_n) where l¹_n is a localization length in the nth channel. Low frequency kinetic behaviour depends on the channel with the maximum localization length l¹₀.     

The longitudinal magnetophonon effect in semiconductors containing magnetic impurities

The dependence of longitudinal magnetoresistance on magnetic field in semiconductors containing magnetic impurities is investigated theoretically. The calculation takes into account the scattering of electrons on magnetic impurities and on optical phonons. The inelastic optical phonon scattering itself is responsible for magnetophonon oscillations of the magnetoresistance, the extremes of these oscillations occuring when energy distance between Landau levels is equal to the energy of optical phonon, $\text{h}\text{?}$ω₀. The scattering on magnetic impurities may lead to spin flip electronic transitions. The spin flip electronic transitions manifest themselves as additional minima on the oscillatory picture of magnetoresistance. These new minima occur when the energy separation between spin-split Landau levels is equal to $\text{h}\text{?}$ω₀.