Effect Of Interlayer Coupling Research Articles

Effect of interlayer coupling on Néel, temperature in copper oxide based antiferromagnets

AbstractThe role of interlayer coupling (J⟂ on the Néel temperature of (1–2–3) compounds is studied by taking the three‐dimensional anisotropic Heisenberg antiferromagnetic model. The two‐sublattice model of the antiferromagnet is considered. The double‐time Green function technique is employed and the higher‐order Green functions are decoupled using the Callen decoupling approximation. The Néel temperature (TN) for YBa2Cu3O6+x (1–2–3) compounds as a function of doping concentrations (x) is estimated. The intraplanar coupling strength (J‖) is treated as a constant throughout the numerical calculations. The theoretical results are compared with that of the random phase approximation (RPA) and existing experimental results.

Magnetic and magneto-optical properties of [formula omitted] multilayers

Co Cu multilayers made by rf sputtering were studied with a vibrating sample magnetometer (VSM), ferromagnetic resonance (FMR) and magneto-optical (MO) spectra. The magnetization increases with decreasing thickness of Cu, which was attributed to the joint effect of interlayer coupling and 2D magnetism. Spin polarization of Cu related to interlayer coupling was indicated from the data of VSM and FMR measurements. The different feature of the experimental and calculated MO spectra further suggested that the Cu is spin polarized and gives an additional MO activity.

CEMS study of Fe-Si/Cr multilayered films

An oscillatory variation of saturation magnetization ( M s) with the thickness of Cr layers has been found in Fe-Si/Cr multilayered films prepared by rf sputtering under 5 mTorr Ar charging pressure. A conversion electron Mössbauer spectroscopy (CEMS) study showed that the oscillatory variation of M s does not result from antiferromagnetic coupling effect, but mainly from an oscillatory change in the paramagnetic component of the Fe-Si layers. This oscillatory change in the paramagnetic component in the Fe-Si layers is due the unusual interlayer coupling effect through the Cr layers.

CEMS study of Fe-Si/Cr multilayered films

An oscillatory variation of saturation magnetization (Ms) with the thickness of Cr layers has been found in Fe-Si/Cr multilayered films prepared by rf sputtering under 5 mTorr Ar charging pressure. A conversion electron Mössbauer spectroscopy (CEMS) study showed that the oscillatory variation of Ms does not result from antiferromagnetic coupling effect, but mainly from an oscillatory change in the paramagnetic component of the Fe-Si layers. This oscillatory change in the paramagnetic component in the Fe-Si layers is due the unusual interlayer coupling effect through the Cr layers.

Interlayer coupling in low temperature magnetoresistance of Si/Nb multilayer films

Interlayer coupling effect in Si/Nb multilayer films was investigated in terms of superconducting fluctuations and weak localization. We found that the coupling effect is strongly related to the transport parameters and the inelastic scattering time gives important information related to the mechanism of the coupling.

Dynamic effects of magnetic multilayer interlayer coupling (FMR modes)

Coupling between magnetic layers in multilayer samples gives rise to dynamic effects which are manifest as anomalous modes in ferromagnetic resonance (FMR) spectra. According to the model presented, antiferromagnetic (ferromagnetic) coupling would produce such modes on the high (low) field side of the uniform FMR mode. Anomalous modes, observed in Fe/Cu and Fe/Cr multilayer samples, are analyzed to obtain coupling constants as a function of nonmagnetic layer thickness. The modes are shown to arise from 180 degrees out-of-phase interlayer magnetization precession. The coupling is observed to be antiferromagnetic in all samples and to be an order of magnitude greater in the Cr system than in the Cu system. >

Effect of interlayer coupling in layered Heisenberg ferromagnets

Nonlinear spin-wave theory is used to study the effect of interlayer coupling on the magnetic properties of layered Heisenberg ferromagnets. Magnetization and specific heat are calculated numerically as functions of temperature and the interlayer coupling strength, and compared with the results on the linear spin-wave theory. At low temperatures, according to the extent the interlayer coupling suppresses the two-dimensional spin fluctuations, we define a characteristic temperature and use it to divide the low-temperature region into two new ones. We give the asymptotic expressions of magnetization, internal energy and specific heat in each low-temperature region using asymptotic expansions of Bessel functions instead of the long-wavelength approximation. The features of dimensional crossover for physical quantities are shown, and a comparison between theory and experiments is made.

Unusual interlayer-coupling effect in Fe-Si/Cr multilayered films.

Fe-Si/Cr multilayered films with amorphous magnetic Fe-Si layers have been prepared with the rf-sputtering method at different Ar charging pressures. Samples with antiferromagnetic exchange coupling can be obtained only at a higher Ar charging pressure, ${\mathit{P}}_{\mathrm{Ar}}$. When ${\mathit{P}}_{\mathrm{Ar}}$=5 mTorr and the Fe-Si layers are as thin as 19 \AA{}, an oscillatory function of magnetization versus the thickness of Cr layers with a period of about 10 \AA{} is obtained. This is an effect specific to interlayer coupling in the multilayered films, and is caused by oscillatory changes of the internal field in Fe-Si layers.

Calculation of the self-energy in a layered two-dimensional electron gas.

The self-energy of a layered two-dimensional (2D) electron gas has been investigated using the Fermi-liquid approach. The zero- and finite-temperature calculations including both single-particle and plasmon excitations have been carried out. It is found that when the interlayer distance is large compared to twice the effective Bohr radius a B , the interlayer-coupling effects are small and the results correspond to those of a pure 2D electron gas. When the interlayer distance is smaller than 2a B , the results are similar to those of a three-dimensional (3D) system. At intermediate interlayer distances, the results show an interesting mixture of 2D and 3D behaviors

Effect of interlayer coupling in a layered antiferromagnet

The effect of interlayer coupling on the magnetic properties of layered antiferromagnets is studied by the use of nonlinear spin-wave theory. The sublattice magnetization, internal energy, specific heat and magnetic susceptibilities are calculated for different interlayer coupling strengths over the whole range of temperatures, and the asymptotic expressions for these quantities are given in two low-temperature regimes distinguished by a characteristic reduced temperature Theta 0 which reflects the character of the layered structure. It is shown that the temperature dependences of the physical quantities have a crossover from three-dimensional to two-dimensional behaviour with increase in the reduced temperature from one regime ( Theta << Theta 0< Theta 1) to another ( Theta 0<< Theta << Theta 1) for small interlayer coupling strengths. The correction due to spin-wave interactions is also discussed.

Compensation temperatures of ferrimagnetic bilayer systems

Compensation points of two ferrimagnetic bilayer systems consisting of two different magnetic layers (A and B) coupled together with a negative interlayer coupling are examined by the use of a new formulation based on both the Ising spin identities and differential operator technique. In particular, the effects of interlayer coupling and crystal-field constant on the compensation temperature are investigated by selecting the layer spins as S A = 1 2 and S B = 3 2 . We have obtained a lot of new phenomena. Some of them may be related to the experimental works of rare-earth/transition-metal multilayer films.

Low-temperature properties of layered Heisenberg ferromagnets.

Spin-wave theory is used to study the effects of interlayer coupling on the properties of layered Heisenberg ferromagnets with S=1/2. The asymptotic expressions of magnetization and specific heat with temperature and interlayer coupling strength (${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$) are given in two low-temperature regimes distinguished by a characteristic temperature ${\mathit{T}}_{0}$=2${\mathit{J}}_{\mathrm{\ensuremath{\perp}}}$/${\mathit{k}}_{\mathit{B}}$. It is shown that the interlayer coupling, though very small, is essential if long-range order at nonzero temperature is to exist.

Effect of Interlayer Coupling on Néel Temperature in Antiferromagnets

AbstractThe Néel temperature is calculated for a 3D Heisenberg model taking into consideration the anisotropy in exchange coupling constant. By virtue of the two‐sublattice approach to antiferromagnets the equation of motion is solved for the Green's function and an expression for Néel temperature is obtained. The higher‐order Green's functions are decoupled by random phase approximation. These expressions are applied to evaluate the Néel temperature of YBa2Cu3O6+x and La2CuO4. The effect of interlayer coupling is examined. The theoretical results are compared with experimental values of Néel temperature.

Dynamics of coupled two-dimensional Cu(Mn) spin-glass films.

Time-dependent susceptibility measurements have been performed on multilayered two-dimensional (2D) 40-\AA{}-wide ${\mathrm{Cu}}_{0.865}$${\mathrm{Mn}}_{0.135}$ spin-glass films, separated by Cu interlayers of width 10${\mathit{w}}_{\mathrm{il}}$1200 \AA{}. It is found that samples with ${\mathit{w}}_{\mathrm{il}}$30 \AA{} display 3D dynamic behavior. For 30${\mathit{w}}_{\mathrm{il}}$600 \AA{} a gradual decoupling of the spin-glass layers occurs, and for ${\mathit{w}}_{\mathrm{il}}$\ensuremath{\ge}600 \AA{} typical 2D behavior is observed. The effect of a finite interlayer coupling on the dynamic susceptibility is a distinct crossover from 2D dynamic behavior at short observation times to 3D dynamic behavior at long times. A clear influence on the spin-glass dynamics is still observable for interlayer thicknesses of order 500 \AA{}; i.e., multilayered spin-glass films are extremely sensitive probes of the effective range of Ruderman-Kittel-Kasuya-Yosida interaction mediated via metallic interlayers. The results also yield information on the relation between time scale and length scale in relaxation experiments, a fundamental concept of domain theories of the spin-glass phase.

Superconductivity in YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices

High-quality YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices with desired thicknesses of each component were fabricated by laser deposition. Superconductivity was studied by varying both YBa/sub 2/Cu/sub 3/O/sub 7/ and PrBa/sub 2/Cu/sub 3/O/sub 7/ layer thicknesses. The results indicate that an isolated single unit cell YBa/sub 2/Cu/sub 3/O/sub 7/ layer (nominal thickness of 12 AA) is superconducting. The increase of T/sub c/ from the lower value of a single unit cell layer to 90 K in thick films and the enhancement of T/sub c/ for a given thickness of YBa/sub 2/Cu/sub 3/O/sub 7/ when the PrBa/sub 2/Cu/sub 3/O/sub 7/ layers decreased to less than approximately 30 AA could be attributed to the interlayer coupling effect. Superconducting transitions of superlattices in an applied magnetic field were studied. The interlayer coupling effect on vortices can be seen by comparing the transition curves in high magnetic fields of thick film, ultrathin film, and superlattice. For the samples with very thin YBa/sub 2/Cu/sub 3/O/sub 7/ layers, similar results to vortex-antivortex pair phase transition were observed by measuring the temperature dependence of resistance, magnetoresistance, and I-V curves, indicating strong two-dimensional behavior in very thin YBa/sub 2/Cu/sub 3/O/sub 7/ films.

Effect of interlayer coupling in YBa2Cu3O7-y

The layered oxide superconductors are essentially two-dimensional in character with a weak coupling between copper oxide planes. Using perturbation arguments of scaling theory, we compare the scaling function in a quasi-two-dimensional layered material with that in a (2+e) dimensional system and relate the interlayer coupling to an effective dimensionality. The effect of interlayer coupling on metallic conduction and superconductivity in YBa2Cu3O7−y is discussed.

Effect of interlayer coupling on superconducting properties: Application to sound attenuation

Interlayer coupling is one of the important issues in understanding transport properties in the normal and superconducting state of the cuprates. Its implications for the superconducting state, such as its role in pairing in the c-direction. are not well understood. New results are presented for longitudinal acoustic attenuation iit a layered/anisotropic superconductor. The calculation focuses on the role of anisotropy in the band structure and in the superconducting order parameter. Measurements of acoustic attenuation are useful as they can provide information on the dielectric response of the charge carriers in the low wavevector q and frequency ω regime.

Mott transition in La 2- xSr xCuO 4: beating Luttinger's theorem

The antiferromagnetic insulating phase in La 2- x Sr x CuO 4 is studied by beginning from a doped Fermi-liquid phase, which undergoes a spin-density-wave-like transition as doping is reduced. Strong correlation effects renormalize the bands near half-filling, until the susceptibility satisfies a Stoner criterion. The ordered phase is predicted to become more incommensurate as doping is increased. A mode-mode coupling formalism is introduced to study the effect of interlayer coupling.

Superconducting and magnetic properties of Gd 1−xPr xBa 2Cu 3O 7−y system

Superconducting and magnetic properties of compounds in the series Gd1−xPrxBa2CU3O7−y(0≤x≤1.0) have been investigated by means of x-ray diffrarction, electrical resistivity and magnetic susceptibility measurements. The depression of superconducting transition temperature Tc described by the classical Abrikosov-Gor'kov pair-breaking theory, hole-filling, and interlayer coupling effect is discussed. Magnetic order in the Gd and Pr rich compounds is observed but suppresses each other. It reflects that the magnetic interactions in GdBa2Cu3O7−y and PrxBa2Cu3O7−y are probably different in nature.

The conductivity and dimensionality crossover of the disordered layered system in a magnetic field

In this paper an interplay between the effects of disorder, interlayer coupling and magnetic field is studied in the disordered layered system. The authors present a crossover effect of dimensionality of the system, which depends on both the magnetic field H and the interlayer coupling t. The corrections of conductivity, Delta sigma j(H,T), corresponding to the maximal crossed diagrams are calculated. It is shown that the conductivities in different directions are anisotropic.