The crystallographic, magnetic, electrical, and magnetoresistive properties of samples of La0.775Sr0.225Mn1−xSnxO3 synthesized by the sol-gel method are studied. It is shown that introducing tin atoms, with their large size, into the manganese sublattice produces significant deformations of the crystal lattice and enhances the structural and magnetic inhomogeneity of the samples. It is discovered that increasing the tin content leads to a reduction in magnetization, a lowering of the Curie temperature, and an increase in the electrical resistivity. The way the crystallographic parameters change is found to correlate with the character of the changes in the magnetic parameters. It is shown that the low-temperature magnetoresistance increases with x, while the magnetoresistance around room temperature is a nonmonotonic function of the tin concentration and has a maximum at x=0.015.

This paper reports on the results of the magnetostatic measurements for Co-Al-O nanogranular films over a wide range of concentrations of the ferromagnetic component x . It has been revealed that grains in the films are characterized by the growth-induced anisotropy with easy axes directed perpendicular to the film plane. The maximum field of the single-grain perpendicular anisotropy reaches ∼2.5 kOe for samples in the vicinity of the percolation threshold ( x ≈ 61 at % Co). It has been established that the characteristic features of the superparamagnetic behavior of an ensemble of oriented Stoner-Wohlfarth particles are retained for the sample with x ≈ 61 at % Co in the presence of the demagnetization field associated with the net magnetization of the film. The influence of the demagnetization field of the film on the shape of the magnetization reversal curves, the coercivity, and the blocking temperature has been investigated and simulated. The results of the simulation are consistent with the experimental data.

We reveal the low-temperature anomaly in the temperature and angular dependencies of the coercivity in granular (CoFeB)x–(SiO2)1−x films with oriented in-plane anisotropy. Namely, at T<100 K the in-plane angular dependence of coercive field acquires two maxima corresponding to easy and hard (in a film plane) directions. This signifies the emergence of coercivity for hard direction in a film plane. The experimental results are explained in terms of a random field model, which describes the onset of spin glass-like correlations in the ensemble of oriented weakly interacting Stoner–Wohlfarth particles.

An anomalous angular dependence of the coercive field of physically nonpercolated granular CoFeB–SiO2 films with oriented anisotropy of the granules, where the presence of the superferromagnetic phase has been established earlier, is observed experimentally at temperatures above the blocking temperature. The angular dependence of the coercive field is similar to that typically observed in the case of magnetization reversal through an inhomogeneous magnetic state of single granules in the ensemble. As the temperature becomes lower than the blocking temperature, the angular dependence changes to that typical of the magnetization reversal through a coherent rotation of granules’ magnetic moments. It is shown theoretically that the anomaly is determined by a singularity of the angular dependence of the critical field causing the absolute loss of the superferromagnetic phase stability in the ensemble of weakly interacting ferromagnetic nanoparticles.

The temperature (4.5–550K) and angular (in the film plane) dependences of the coercivity field for physically nonpercolated nanogranular (CoFeB)x–(SiO2)1−x films with an oriented intraplane granule anisotropy have some unusual properties compared to those owing to blocking of thermally activated reorientation of the magnetic moments of the granules. At temperatures above the blocking temperature Tb≈350–370K, the dependence of the coercivity on the measurement duration is weak compared to that below Tb. Its angular (in the film plane) dependence differs qualitatively from that expected with blocking of superparamagnetic particles. This behavior is explained by the appearance of superferromagnetic ordering of the granule magnetic moments at T>Tb owing to interactions among them. As the temperature is reduced below 100K, the coercive field Hc for magnetization in the easy direction increases significantly more than expected for a blocked superparamagnetic ensemble. Here Hc≠0 for magnetization along the hard direction in the plane. The angular (in-plane) dependence of Hc acquires two maxima, along the easy and hard (in-plane) directions. This phenomenon is explained by the appearance of superspin-glass correlations in the mutual orientations of the granule magnetic moments of the ensemble.

In order to study the magnetic interactions influence on the relaxation processes in superparamagnetic media, the magnetostatic measurements were carried out for the granular (CoFeB)x-(SiO2)1-x films with x values near percolation threshold. The observed temperature dependences of the coercivity for the samples magnetized along in-plane easy axis have shown two parts linear on with different inclination angles, which cross each other at the blocking temperature (Tb). The first part of the curve, which corresponds to the temperature range below Tb, depends on the measuring time and is related to the thermal activation nature of magnetization reversal process in the blocked superparamagnetic state. Second part of the curve, which corresponds to the temperature range above Tb, is practically independent on the measuring time and is related to existence of correlated state of superparamagnetic grains moments, i.e. to superferromagnetic state. The method of the magnetization reversal curves simulation based on the numerical solving of kinetic equation has been applied to explain the experimental results.

The influence of interparticle interaction on the processes of magnetization reversal is considered for an ensemble of oriented Stoner–Wohlfarth nanoparticles. This is done through a solution of a kinetic equation describing the relaxation of the total magnetization to its equilibrium value in an effective mean field which includes a term proportional to the instantaneous value of the magnetization. It is shown that the interparticle interaction influences the temperature dependence of a coercive field. Under certain conditions, the presence of the interparticle interaction can lead to the formation of the so-called superferromagnetic state with the correlated directions of the magnetic moments of the particles. If the system is unable to come to the equilibrium during the time interval necessary to perform measurements, some measured quantities become dependent on the measurement time. It is shown that the blocking temperature Tb and the temperature dependence of coercive field at TTb, however, the coercivity, if exists, does not depend on the measurement time. The data of magnetostatic measurements, carried out on the (CoFeB)x–(SiO2)1−x nanogranular films with the concentration of ferromagnetic particles slightly lower than a percolation threshold, are in compliance with the results of the calculations.

It is observed experimentally that the coercive field has an anomalous angular dependence at temperatures above the blocking temperature in physically nonpercolated granular films CoFeB-SiO$_{2}$ with anisotropic granules oriented in the same direction. It is shown that the anomaly is determined by the singularity of an angular dependence of the critical field causing the absolute loss of phase stability of the superferromagnetic state of an ensemble of interacting superparamagnetic granules.

We report magnetostatic measurements for granulated films (CoFeB)_x-(SiO_2)_1-x with fabrication induced intraplanar anisotropy. The measurements have been performed in the film plane in the wide temperature interval 4.5÷300 K. They demonstrate that above films have low-temperature anomaly below the percolation threshold for conductivity. The essence of the above peculiarity is that below 100 K the temperature dependence of coercive field for magnetization along easy direction deviates strongly from Neel-Brown law. At temperature lowering, the sharp increase of coercivity is observed, accompanied by the appearance of coercive field for magnetization along hard direction in the film plane. We establish that observed effect is related to the properties of individual ferromagnetic granules. The effect weakens as granules merge into conglomerates at x higher then percolation threshold and disappears completely at x>1. We explain the above effect as a consequence of the difference in thermal expansion coefficients of granule and cover material. At temperature lowering this difference weakens the envelopment of an individual granule by the cover matrix material, thus permitting to realize the spontaneous magnetostriction of a granule. The latter induces an additional anisotropy with new easy axis of a granule magnetization along the external magnetic field direction. Our explanation is tested and corroborated by the ferromagnetic resonance measurements in the films at T = 300 K and T = 77 K.

Magnetostatic, magnetoresonance (FMR), and magnetotransport measurements are performed in the temperature range 100–360K in the granular ferromagnetic film Co0.59(Al2On)0.41 possessing isotropic (independent of the angle between the direction of the current and magnetization in the plane) positive magnetoresistance in magnetic fields ±500Oe are performed. It is established that this anomaly of the magnetoresistance is due to short-range order effects in the ordering imposed on the magnetic moments of granules in the absence of an external magnetic field by their dipole–dipole interaction. It is established that the blocking temperature of thermally activated re-orientations of the magnetic moments of the granules differs substantially with respect to the measurement time and the methods used for this investigation. It is about 200K for magnetization measurements and exceeds 470K for FMR and measurements of the magnetoresistance. It is shown that ferromagnetic resonance in the present system changes from the regime “independent resonance of individual clusters” to the regime “collective resonance of a system of magnetic granules in a film” when the direction of the magnetic field changes from in-plane to normal to the film.

Temperature and field investigations of the magnetic properties of multilayer films, consisting of a sequence of alternating magnetic layers of iron and the rare-earth terbium separated by layers of nonmagnetic gold, are performed. The samples were obtained by electron-beam deposition. The field dependence of the magnetic moment of a film with H∥n are analyzed to determine the characteristics of the uniaxial anisotropy. It is shown that a nonuniform uniaxial anisotropy results in nonlinearity in the magnetization of the film in H∥n. The process of magnetization of a film in H⊥n, when the transition to a single-domain state occurs only as a result of the motion of domain walls, is described. It is shown on the basis of the data on the field dependences of the magnetic moment at low temperatures that the magnetic moments of the Fe and Tb layers are oriented oppositely with respect to one another. A compensation point is observed in the temperature dependence of the magnetization; this indicates the presence of antiferromagnetic coupling between the Fe and Tb layers.

We study the formation of antiferromagnetic magnetoelastic domains in easy-plane antiferromagnets of the iron-group dihalides, in which the infinite degeneracy of the spatial orientation of the antiferromagnetic vector in the basal plane is lifted on account of the spontaneous magnetostriction. In these crystals the domains differ from each other not only by the direction of the antiferromagnetic vector L in them but also by the related directions of the principal axes of the spontaneous magneostrictive strain. The system of antiferromagnetic domains turns out to be identical to the system of elastic domains. It is shown that the processes of magnetization and the induced striction in a magnetic field in the multidomain antiferromagnetic state are interconnected. Data on the field dependence of the induced magnetostriction in the multidomain state of the easy-plane antiferromagnets CoCl2 and NiCl2 are presented and analyzed. It is shown that although the magnetostriction in the cycles of imposition and removal of the magnetic field includes both reversible and irreversible contributions, the reversible being the main one. It is shown that the magnetoelastic-striction domains are responsible for reversibility (equilibrium) of the multidomain state. The field dependence of the magnetostriction of the uniform and multidomain states and the behavior of the magnetization of the crystals are described. For description of the rearrangement of the multidomain state, the approximation of a continuous distribution of domains with respect to the orientations of their L vector in the easy plane of the crystal in the absence of external magnetic field. It is shown that the matching of the elastic fields of the system of domains and the elastic fields of defects can bring about the formation of a reversible multidomain state, i.e., it can make such a state energetically favorable. The results of the analysis are in satisfactory agreement with the experimental data.

An analysis is made of the experimental data on the magnetic-field dependence of the magnetostriction and magnetization of the NiCl2 crystal at its transition from the multidomain antiferromagnetic state to a uniform state. It is shown that their field dependence is determined by the mean orientation of the domains, which is characterized by a domain coalignment parameter. That parameter is used to give a phenomenological description of the multidomain state of the antiferromagnet NiCl2.

The main object of this research was the definition of optimal meaning degree of development for photographic films for getting the best characteristics of tone reproduction. The database of tone reproduction parameters of the photographic systems with digital image processing was created on the basis of construction of objective tone reproduction curve and calibration curves. Subsequent scanning negative image was applied. The cameras (Canon F1, Nikon F4, Pentax MZ-6, Pentax MZ-7), the films Kodak T-Max 100, 400, Ilford 100 and the developer D-76 were used in our experiments. The standard gray scale was used as test-object for taking photos. The films were developed up to various average gradient values in the interval 0.55 -0.90 for the definition of optimum development degree. According to the technique, developed by us (the "Mirror" program), the curves of objective tone reproduction have been constructed for all shooting and processing specified conditions. At the same time the image quality was visually estimated up on shooting objects (picture, portrait, landscape etc). The submitted results convincingly confirm necessity of an establishment of different degrees of development for black-and-white still-picture films and movie films. The analysis of objective tone reproduction curves allows to make conclusion, that the optimum meaning of average gradient for photographic films should be in an interval 0.80-0.85.

We analyzed the field dependences of forced magnetostriction in the multidomain state of the easy-plane antiferromagnet CoCl2 obtained in the following cycles: the introduction-removal of a magnetic field lying in the easy plane, the introduction-removal of a magnetic field lying in the easy plane and directed normally to that introduced earlier, etc. The magnetostriction of the crystal in the multidomain state was shown to contain two components. First, the component reversible in the cycle magnetic field introduction-removal, which makes the major contribution in the crystal under consideration, and, second, a comparatively small irreversible component, that is, the contribution retained after magnetic field removal. In low fields, the reversible magnetostriction component was proportional to the square of the applied magnetic field. Field-induced rearrangement of the multidomain antiferromagnetic state was found to be responsible for singularities of the field dependence of crystal magnetization. In particular, in a near-zero field that lay in the easy plane, the transverse susceptibility decreased twofold compared with its value in fields in which the crystal is already in the monodomain state. At the same time, close to the “monodomainization” field, transverse magnetic susceptibility was maximum. Defects were shown to favor the formation of the reversible multidomain state. Determining factors in this process were elastic and magnetoelastic interactions. The multidomain state of antiferromagnets was described using the domain distribution function over the orientations of domain antiferromagnetic vectors with respect to the magnetic field direction and the magnetic field dependence of this function. The results of our analysis were in close agreement with the experimental data on CoCl2.

The forced magnetostriction and magnetization are measured in the easy-plane-type two-sublattice NiCl2 antiferromagnet (AFM) in the case where this AFM passes from the multidomain to a single-domain state. It is shown that, in accordance with the magnetoelastic nature of the multidomain state, the field dependences of the forced magnetostriction and magnetization are interrelated and affected by the transition from the multidomain to the single-domain state. The character of these dependences corresponds to the case where the magnetization and striction are proportional to the number of domains with an energetically favored orientation with respect to the external magnetic field.

Experimental data from measurements of the induced magnetostriction of the easy-plane two-sublattice layered antiferromagnet NiCl2 in the homogeneous and multidomain states at T=4.2 K are analyzed. It is shown that the intersublattice magnetoelastic interactions are dominant in NiCl2. The induced magnetostriction of the crystal in the single-domain state is due to canting of the spins of the sublattices toward the magnetic field direction. The induced magnetostriction in the multidomain state is due to a rearrangement of the domain structure and is independent of the small in-plane anisotropy. In both cases the values of the induced magnetostriction are directly proportional to the square of the value of the external magnetic field.

It is shown that anomalies of the temperature dependence of distortion of NiCl2 crystals, in the paramagnetic region (T > T-N), can be described with recourse of the mechanism of biquadratic non-Heisenberg isotropic interactions of the fourth order with respect to the spin. These anomalies are due to spontaneous increase in the quadrupole magnetic moment.