Compensation point (or points) of nanoscaled transverse Ising thin films: effects of surface dilution

The phase diagram (critical temperature and compensation temperature) and the total magnetizations in a nanoscaled transverse Ising thin film with thickness L and a negative interlayer coupling at the surfaces are investigated by the use of both the effective-field theory with correlations and the mean-field theory. Particular emphasis is given to the effects of the surface and its dilution on them. We have found that, for appropriate values of the system parameters, compensation point (or points) may be obtained in the present system with L?=?5 (or L?=?10).     

Characteristic phenomena in nanoscaled transverse Ising thin films with diluted surfaces

The phase diagrams and magnetizations of two nanoscaled thin films with a negative interlayer interaction and dilution at the surfaces, described by the transverse Ising model, are investigated by the use of the effective field theory with correlations. A lot of characteristic phenomena which heavily depend on the surface parameters can be found in them. In particular, the behaviors of a compensation point (or points) in these nanosystems with a negative interlayer interaction at the surfaces are examined by changing the transverse field and the physical parameters at the surfaces.     

The random transverse Ising thin film with decorated ferrimagnetic surfaces

The phase diagrams and magnetization curves of the random transverse Ising film with decorated spin-1 atoms on the surface are investigated by the use of an effective field method within the framework of a single cluster theory. In particular, the case in which decorated atoms at the surfaces are ordered ferrimagnetically is examined. The effects of the interactions, random transverse field at the surface and in the bulk, and film thickness are studied. A number of characteristic phenomena, such as the possibility of compensation points on the surfaces and in the film are found.     

Ferrimagnetism in two antiferromagnetic transverse Ising thin films

The phase diagrams and temperature dependences of total magnetization m_T in two antiferromagnetic transverse Ising thin films with same thickness L (L = 4), consisting of two (A and B) layers, are studied by the uses of the effective-field theory with correlations and the mean-field theory. The A and B layers are consisted of spin-1/2 atoms and they have opposite spin directions. Two magnetic structures are discussed and they exhibit rather different and characteristic behaviors for the magnetic properties. Many characteristic behaviors observed in standard ferrimagnetic materials as well as novel phenomena have been obtained for the thermal variations of m_T in the both systems, when the crystallographically equivalent conditions between the A and B layers are broken.     

Effects of the transverse Ising model parameters on the polarizations of multi-surface ferroelectric thin films

The layer polarizations and average polarizations of multi-surface ferroelectric thin films described by the transverse Ising model (TIM) have been studied within the framework of a Green’s function technique. The effects of the exchange interactions and transverse field parameters on the polarizations are discussed systemically. By performing a higher-order decoupling to the Fermi-type Green’s functions, the numerical results beyond those of the usual mean-field approximation are obtained. It is shown that the larger the exchange interaction, the larger the layer polarization and the average polarization; the larger the transverse field, the smaller the polarization.     

The possibility of re-entrant phenomena induced by a transverse field in ultra-thin transverse Ising films

The phase diagrams and temperature dependences of magnetizations in ultra-thin transverse Ising thin films are studied by the use of both the effective-field theory with correlations (EFT) and the mean-field theory (MFA). Novel features, such as the possibility of re-entrant phenomena, are obtained for the magnetic properties in such systems with a zero transverse field at the surfaces, when the EFT is applied to them, although such features could not be found from the use of the MFA. When the transverse field at the surfaces takes a finite value, however, the re-entrant phenomena could not be found from the both formulations of the EFT and the MFA. Similar phenomena are then obtained in the phase diagrams by using the MFA and the EFT.     

Ferrimagnetic magnetizations of transverse Ising thin films with diluted surfaces

The temperature dependences of longitudinal and transverse magnetizations in transverse Ising thin films with diluted surfaces which are coupled antiferromagnetically to the bulk are studied by the use of the effective-field theory (EFT) with correlations. Novel features are obtained for the thermal variations of longitudinal magnetization, being different from those of the bulk ferrimagnetic materials, such as the possibility of two compensation points. They are depending on the thickness of a film and the surface dilution. These characteristic phenomena come from the competition between the surfaces and the bulk when the ratios of the physical parameters (transverse field and exchange interaction) between the surfaces and the bulk are selected as some large values.     

Phase diagrams of a cylindrical transverse Ising ferrimagnetic nanotube; Effects of surface dilution

Phase diagrams (transition temperature and compensation temperature) of a cylindrical ferrimagnetic nanotube with a negative core–shell interaction, described by the transverse Ising model (TIM), are investigated by the use of the effective-field theory with correlations. The phase diagrams of the system are strongly affected by the surface dilution. The possibility of two compensation points is found in the phase diagram, in contrast to the case of a cylindrical TIM nanowire.     

The compensation temperature study of the mixed Ising ferrimagnetic spin system with crystal field in a transverse field

Abstract. The magnetic properties of the nearest-neighbor interaction mixed spin-1/2 and spin-1 Ising ferrimagnetic spin system with crystal field in a transverse field are investigated within the framework of the effective-field theory. Particular emphasis is given to the honeycomb lattice with coordination number Z = 3 for which magnetizations are obtained. If transverse field Ω varies in the certain ranges, we find that the compensation temperature is obtained for the value of the crystal field D in a restricted region. We discuss in detail the influence of the transverse field on the behaviors of the compensation point and magnetization curves in this paper.     

Optically induced transverse voltages in thin metal films

Results of experiments on laser induced voltages in metal films are summarized. The voltages are found to occur along certain directions in the plane of slant-angle vapour deposited films. A thermo-electric model based on periodic variations in the microscopic film structure, is described. The magnitude of the effect is proportional to the absorbed power/length between the contact points. Application of the films in the wavelength range 0.33–10.6μm is described and compared to more conventional detectors. A recent application, using the effect as a tool to profile non-uniformities in thin films, is also discussed.     

Construction of phase diagrams for nanoscaled Ising thin films on the honeycomb lattice using cellular automata simulation approach

The phase diagrams of the three-layer Ising model on the honeycomb lattice with a diluted surface have been constructed using the probabilistic cellular automata based on Glauber algorithm. The effects of the exchange interactions on the phase diagrams have been investigated. A general mathematical expression for the critical temperature is obtained in terms of relative coupling r = J₁/J and Δ_s = (J_s/J) ? 1, where J and J_s represent the nearest neighbor coupling within inner- and surface-layers, respectively, and each magnetic site in the surface-layer is coupled with the nearest neighbor site in the inner-layer via the exchange coupling J₁. In the case of antiferromagnetic coupling between surface-layer and inner-layer, system reveals many interesting phenomena, such as the possibility of existence of compensation line before the critical temperature.     

The possibility of two compensation points in a ferrimagnetic mixed spin-1 and spin-3/2 Ising system using Bethe lattice approach

We give an exact formulation of a mixed spin-1 and spin-3/2 Ising model on the Bethe lattice, which shows ferrimagnetism and compensation points. The model incorporates antiferromagnetic nearest-neighbor interaction which is relevant to describe ferrimagnetism. The influence of two sublattice crystal fields, D_A and D_B, on compensation points is studied in detail. For certain crystal-field values, the single or double compensation temperature may occur in the present system.     

LPE-like growth of YIG ferrimagnetic thin films by pulsed laser ablation with molten droplets

Yttrium iron garnet (YIG) films were grown by pulsed laser ablation (PLA) on (111) Gadolinium Gallium Garnet (GGG) substrates. The second harmonic of YAG laser (532 nm) with a high laser fluence was employed to produce YIG droplets efficiently. It was found that YIG films prepared at RT substrates have a large number of solidified droplets of various sizes. Highly oriented YIG crystals were grown on the (111) GGG substrate heated at 860 °C by PLA using a large number of molten droplets, suggesting an LPE-like growth. This YIG film shows a small ferrimagnetic resonance linewidth of 7.5 Oe. This value is quite small for films prepared by vapor-phase epitaxy techniques.     

Effective scaling behavior of magnetization and Hamming distance in Ising thin films under a surface field

The recent improvements on the technology for developing high-quality thin magnetic films has renewed the interest in the study of surface effects in both static and dynamic magnetic responses. In this work, we use a Monte-Carlo algorithm with Metropolis dynamics together with a spreading of damage technique to study the interplay between the effects of finite thickness and surface ordering field in thin ferromagnetic Ising (S=1/2) films. We calculate, near the bulk critical temperature and several values of the surface field, the dependence on the film thickness of the average magnetization M and Hamming distance D. We employ a finite size scaling analysis to show that both obey an effective one-parameter scaling but exhibit distinct characteristic surface fields. At their corresponding characteristic surface fields both M and D become roughly thickness independent and we estimate the critical exponent characterizing the behavior of the typical scaling lengths. Received 29 March 1999 and Received in final form 21 April 1999     

A kinetic Monte Carlo study for stripe-like magnetic domains in ferrimagnetic thin films

The topology and dynamics of stripe-like magnetic domains obtained in a ferrimagnetic garnet subjected to a time-dependent external magnetic field is studied experimentally and theoretically. Experiments are performed on a commercially available magnetic bubble apparatus, allowing the observation of the time-evolution of the magnetic domain structure. The system is modeled by a meso-scale Ising-type lattice model. Exchange and dipolar interactions between the spins, and interaction of the spins with the external magnetic field are considered. The model is investigated by kinetic Monte Carlo simulations with time-varying transition rates. In the limit of low temperatures the elaborated model leads to a magnetic domain topology and dynamics that is similar to the ones observed in the experiments. In the highly non-equilibrium limit with a high driving frequency the model reproduces the experimentally recorded hysteresis loops as well.     

High-energy ion induced physical and surface modifications in antimony sulphide thin films

Sb₂S₃ thin films prepared by electrodeposition on indium tin oxide coated glass substrate were irradiated with 150 MeV Ni¹¹⁺ ions for various fluence in the range of 10¹¹–10¹³ ions/cm². The modifications in the structure, surface morphology and optical properties have been studied as a function of ion fluence. X-ray diffraction (XRD) analysis indicates a shift in the (2 4 0) peak position towards lower diffraction angle and a decrease in grain size with increase in ion fluence. Presence of microcracks due to irradiation induced grain splitting effect has been observed from the SEM micrograph at higher ion fluence. The optical absorbance spectrum revealed a shift in the fundamental absorption edge and the band gap energy increased from a value of 1.63 eV for as-deposited films to 1.80 eV for the films irradiated with 10¹³ ions/cm².     

Swift heavy ion induced surface modifications in nano-crystalline Li-Mg ferrite thin films

The swift heavy ion (190 MeV Au¹⁴⁺) induced modifications in surface morphologies of the nanocrystals of ferrite thin films have been extensively studied through the images of atomic force microscopy (AFM). In most of the irradiated films significant features like, the ditch and dike structures, have been observed through out the surface. We try to explain the observed changes on the basis of thermal spike model followed by momentum transfer induced lateral mass transport. In addition to these changes some new and interesting features have been noticed after irradiation in 8F and 9F ferrite thin films. These new features are attributed to sputtering phenomenon due to the presence of defects like latent tracks.     

Strain evolution and morphological transition of magnetron-sputtered CeO2 thin films induced by deposition parameters

Cerium dioxide (CeO₂) films were fabricated on yttria-stabilized zirconia (YSZ) single crystals using unbalanced radio frequency (RF) magnetron sputtering. X-ray diffraction measurements revealed film strain discrepancies under different deposition parameters. Strain evolution was induced by varying sputtering pressure, RF power, and sputtering gas. A distinct morphological transition from a granular surface to an interwoven surface was also realized by varying the above parameters. On the basis of the “atomic peening” mechanism, the influence of different parameters on film strain was discussed. The film surface characteristics were revealed to be highly correlated with film strain. YBa₂Cu₃O_7−δ (YBCO) films were post-deposited on the as-grown CeO₂/YSZ(001) stack by using the trifluoroacetate metal-organic deposition (TFA-MOD) method. The superconducting property of the YBCO layer varied significantly with the morphology of the CeO₂ buffer films.     

Electron transport in thin metal films having ionized impurities and unequal surface specularity parameters

Summary In this paper analytical expressions for the electrical conductivity and thermoelectric power of thin metal films have been calculated for films containing ionized impuritiesand having unequal surface specularity parameters. The effects of alteration in the energy dependence of the electron relaxation time as well as unequal probabilities of scattering from the two surfaces are thus completely taken into account.