Ferrite Single Crystals Research Articles

Molecular dynamics study on the effect of ferrite structure on the mechanical characteristics of pearlite

Cold-drawn pearlitic steel wire has a wide range of applications in engineering due to its excellent mechanical properties. However, to date, there is limited understanding of how the internal ferrite phase structure of pearlitic steel wire affects its mechanical properties. The effect of the ferrite phase structure on the deformation mechanism and mechanical properties of pearlite was studied using molecular dynamics methods. The study considered three types of ferrite structures: (1) single-crystal structure, (2) nanocrystalline structure and (3) twinned crystal structure. The study showed that the ferrite structure could alter the deformation mechanism of pearlite during tensile loading by affecting the plastic deformation behaviour of ferrite. When the ferrite is a single-crystal structure, the pearlite undergoes elastic deformation followed by direct fracture failure; when the ferrite is a nanocrystalline structure, the pearlite experiences elastic deformation, elastic-plastic deformation, plastic deformation and then fracture failure in sequence; when the ferrite is a twin structure, the pearlite undergoes elastic deformation, plastic deformation and then fracture failure in sequence. Due to the influence of the deformation mechanism, the mechanical properties of pearlite with different ferrite structures showed a significant difference. Compared to single-crystal ferrite, when the ferrite structure is nanocrystalline, the strength of pearlite decreases significantly, but the ductility is significantly increased. Moreover, the ductility increases as the size of the nanocrystals decreases. Compared to single-crystal ferrite, when the ferrite has a twinned structure, the strength of the pearlite remains unchanged, but the ductility significantly increases. In addition, the ductility increases as the thickness of the twin layers decreases. The research results provide a new approach for further improving the mechanical properties of cold-drawn pearlitic steel wire.

Study of the influence of gamma irradiation on ferrite-spinel monocrystals

The mechanisms of redistribution of metal ions and the formation of defects in ferrite spinel upon irradiation are complex and depend on a number of factors. Therefore, computer simulations and experimental studies are important for understanding the behavior of the physical properties of these materials under the influence of radiation. The development of new materials that can withstand radiation damage is of great importance for a range of applications, including solid state physics, nuclear physics, space research and medical applications. In this work, the effect of gamma irradiation on Co0,75Cu0,25Fe2O4 ferrite single crystals has been investigated. An earlier study using Mössbauer spectroscopy was carried out to determine the changes in the metal ion content in the sublattices of ferrite spinels. These changes affect the magnetic crystallographic anisotropy of the material [1]. Data can be found in the scientific literature that indicate that gamma irradiation leads to changes in the magnetic susceptibility of materials and to changes in the magnetization curve [2,3]. These changes in physical properties can be explained by redistribution of metal ions in octahedral and tetrahedral sublattices, since metal ions in sublattices have splitting of atomic levels.

Влияние остаточных напряжений в стали У8 с грубопластинчатым перлитом на магнитную проницаемость

The physical reasons for the formation of peaks of that part of the magnetic permeability, which is caused by transitions of only 90-degree domain boundaries µ90(H0) in deformed steel U8 with coarse-plate perlite when the field changes along the back of the hysteresis loop, are considered. It is shown that the orientation relations of the Patch-Pitch between single-crystal ferrite and cementite plates in U8 steel lead to the appearance of a constant angle between the magnetic moments of these plates and, consequently, to the appearance of corresponding local scattering fields. The latter can significantly affect the values of the peak fields of the curve µ90(H0). Theoretical expressions for these fields containing contributions of scattering fields that should be taken into account when determining residual compressive stresses are obtained. It is also shown that to determine the residual stresses, two expressions for peak fields are not enough, and additional experiments are needed, as which it is proposed to use the dependences of the coercive force on elastic tensile stresses. This leads to a complication of the algorithm for determining residual compressive stresses in comparison with the case of low-carbon steels. A method for estimating the values of local scattering fields in the ferrite parts of U8 steel grains with residual compressive stresses is proposed.

Estimation of residual compressive stresses in deformed U8 steels with coarse-plate perlite by field dependences of magnetic permeability

The physical reasons for the formation of peaks of that part of the magnetic permeability, which is caused by transitions of only 90-degree domain boundaries μ90(H0) in deformed steel U8 with coarse-plate perlite when the field changes along the back of the hysteresis loop, are considered. It is shown that the orientation relations of the Patch-Pitch between single-crystal ferrite and cementite plates in U8 steel lead to the appearance of a constant angle between the magnetic moments of these plates and, consequently, to the appearance of corresponding local scattering fields. The latter can significantly affect the values of the peak fields of the curve μ90(H0). Theoretical expressions for these fields containing contributions of scattering fields that should be taken into account when determining residual compressive stresses are obtained. It is also shown that to determine the residual stresses, two expressions for peak fields are not enough, and additional experiments are needed, as which it is proposed to use the dependences of the coercive force on elastic tensile stresses. This leads to a complication of the algorithm for determining residual compressive stresses in comparison with the case of low-carbon steels. A method for estimating the values of local scattering fields in the ferrite parts of U8 steel grains with residual compressive stresses is proposed. Keywords: residual compressive stresses, deformed steel U8 with coarse-plate perlite, magnetic field, magnetization, magnetic permeability, 90-degree domain boundaries (DB), large-angle vicinity(LAV) and small-angle (SAV) grain boundaries of steel, orientation relations of the Patch-Pitch.

Anisotropic Magnetoabsorption of Light in Cobalt Ferrite and Its Correlation with Magnetostriction

The absorption spectra of a CoFe2O4 ferrite spinal single crystal, which has a giant magnetostriction, demonstrate an absorption edge at 1.18 eV and a fine structure of impurity absorption bands in the IR region. In the Voight geometry, the crystal is shown to exhibit magnetoabsorption, which is related to the field-induced changes in the fundamental absorption edge and impurity absorption bands. The magnetoabsorption (magnetotransmission and magnetoreflection of light) is anisotropic and depends on the magnetic field direction with respect to the crystallographic axes of the crystal. The light magnetoabsorption is found to be related to the magnetostriction of the crystal. The magnetostriction of CoFe2O4 is shown to significantly contribute to its magnetic anisotropy constant, which is accompanied by changes in the electronic spectrum and optical properties when a magnetic field is applied. The high magnetoabsorption in CoFe2O4 in a relatively low magnetic field makes it possible to use this magnetic material for the development of a new trend in spintronics, namely, strain-magnetooptics.

Single-crystal growth and magnetic properties of Co-substituted Ca–La magnetoplumbite-type ferrite

Using the flux method, we successfully synthesized Co-substituted Ca–La magnetoplumbite-type ferrite single crystals, CaxLayFezCowO19 (Ca–La–Co system), a base material for high-performance hard ferrite magnets. Wavelength-dispersive X-ray analysis revealed that the chemical compositions of the obtained crystals depended on both the starting composition and reaction atmosphere. The fraction of Fe + Co to Ca + La deviates from the canonical value of 12, and the Co content, which is essential in magnetic anisotropy, improves with the synthesis under an oxygen gas stream. In addition, the magnetic anisotropy is enhanced by the Co substitution, as expected, but also depends on the Ca/La ratio, suggesting an appreciable effect of Fe2+. The magnetocrystalline anisotropy can be larger in the Ca–La–Co system than in the Sr–La–Co system.

Giant spontaneous exchange bias obtained by tuning magnetic compensation in samarium ferrite single crystals.

Spontaneous exchange bias (SEB) under zero field cooling (ZFC) has recently attracted lots of attention due to its underlying physics and potential applications. Here we report the giant SEB (GSEB) of SmFeO3 single crystals by tuning magnetic compensation by temperature, which is rather convenient. A SEB field of up to 1 T at 3.9 K after ZFC (-1.4 T at 3.9 K after field cooling) was obtained. The SEB shows reciprocal relationship with remnant magnetization.

Self-excitation upon nonlinear ferromagnetic resonance

Results from an experimental study of self-excitation in ferrite single crystals upon nonlinear ferromagnetic resonance are considered. The dependences of the frequency and amplitude of self-oscillations on the microwave power and the intensity of oscillation anisotropy are obtained. Self-excitation is of interest because it is the only effect not induced by noise in strongly excited matter.

Crystal Plasticity Finite-element Simulation on Development of Dislocation Structures in BCC Ferritic Single Crystals

Crystal Plasticity Finite-element Simulation on Development of Dislocation Structures in BCC Ferritic Single Crystals

A differential-exponential hardening law for non-Schmid crystal plasticity finite element modeling of ferrite single crystals

Crystal plasticity finite element (CPFE) modeling of multi-phase, third generation advanced high strength steel (3GAHSS) requires finding the hardening parameters of slip systems operating in different phases (e.g. FCC, BCC, BCT). It is common to see the Schmid law used to model the deformation of BCC crystals. However, researches by Bassani and others have shown that BCC crystals could obey the non-Schmid law. In this paper we examined the differences between using a CPFE model based on the Schmid versus a non-Schmid law to model the uniaxial compression of single crystal ferrite micropillars with distinct orientations carved out of dual phase DP980 and three-phase QP980 steel sheets. To accurately model the changing hardening rate of the single crystal, a new exponential hardening model was developed that would differentially harden slip systems. Criteria for transitioning from stage I to stage II hardening of single crystals were also developed and verified.Finally, it was shown that it is not sufficient to use only one single crystal micropillar compression force-displacement curve for the calibration of the non-Schmid CPFE model. The predictions of the resulting model would be unreliable, and its accuracy highly dependent on the orientation of the micropillar chosen for calibration. However, when two mircopillar compression force-displacement curves were used for calibration, the model's predictions were consistently accurate. Using more than two curves for calibration did not result in significant improvements.

Flux growth of magnetoplumbite-type strontium ferrite single crystals with La–Co co-substitution

The Na2O flux method was successfully applied in the single crystal synthesis of the magnetoplumbite-type strontium ferrite with La–Co co-substitution (Sr1−xLaxFe12−yCoyO19), which is a familiar base material for commercial permanent magnets. The initial amount of Na2O flux was fixed in the molar ratio of Na/(Sr+La)=5.17. Composition analysis revealed discordance between La and Co concentrations (x>y) in the obtained crystals, indicating that the extra charge introduced by the Co2+ substitution for Fe3+ is not compensated by La3+ for Sr2+. In the present growth condition, the necessary amount of La is nearly twice that of Co (y/x≃0.55), suggesting valence instability of an appreciable amount of Fe3+ to Fe2+. Single crystalline magnetization measurements showed that the substitution markedly enhances the magnetic anisotropy and slightly raises the saturation magnetization. Remaining problems, which should be resolved before the experimental determination of the Co site occupation, are also discussed.

Выращивание монокристаллов феррита стронция из раствора

The results of the growth of strontium ferrite single crystals from the Na 2 O based flux using the method of spontaneous crystallization are presented. For the growth experiments the resistive furnace with the PID temperature controller was used. Iron oxide Fe 2 O 3 and strontium carbonate SrСO 3 were used as basic materials. Black single crystals with a typical hexagonal shape and sizes of 2–5 mm were obtained. Also black powders were obtained. The structural and morphological characterization of the grown hexaferrites was performed by X-ray diffraction and the scanning electron microscopy (SEM), respectively. An X-ray analysis of the grown samples was measured with the scan speed 1°/min from 10 to 90°. For this aim the powder X-ray diffractometer Rigaku Ultima IV was used. Cell parameters were obtained: а = 5.8832(4) Å, с = 23.0361(14) Å, V = 690.51(6) Å 3 . These data are in a good agreement with the previously published data. An X-ray analysis of the Na 2 CO 3 solution revealed additional phases. The grown crystals were tested with the scanning electron microscopy Jeol JSM-7001F. Uniform distribution of Fe and Sr ions was proved. Element distribution detected that the material had a single phase structure.

Mn-Znフェライト単結晶の初透磁率に及ぼす応力効果の異方性

Manganese Zinc ferrite single crystals have been widely used for making video cassette recorder (VCR) heads. The initial permeability is one index relating to the performance of magnetic heads. It was known that the initial permeability of the crystals decreased as a function of residual stresses left after machining of the magnetic heads. At that time, most of the crystals were grown in the Bridgman furnace, so that compositional segregation could not be avoided and no research work was systematically carried out on the relationship between anisotropic stress effects and initial permeability of the crystals. For the tensile and compressive samples we used very uniform single crystals of less than 0.1mol% compositional segregation, produced by solid phase reaction. The variously orientated crystal samples, shaped like picture frames, were cut by ultrasonic machining and etched more than 20μm deep by a heat phosphoric acid to remove residual stresses. The initial permeability was measured during tensile and compressive tests as a parameter of frequency from 100kHz to 100MHz, in a temperature-controlled silicon oil bath. The initial permeability of the crystal samples under uniaxial stress was also obtained theoretically by the magnetocrystalline anisotropy energy due to the rotation magnetization. It was found that the initial permeability at 50MHz might be improved by more than 10dB by applying the tensile stress of 25MPa at <100> direction. This phenomenon may be applied to other applications.

Complementary use of monochromatic and white-beam X-ray micro-diffraction for the investigation of ancient materials

Archaeological artefacts are often heterogeneous materials where several phases coexist in a wide grain size distribution. Most of the time, retrieving structure information at the micrometre scale is of great importance for these materials. Particularly, the organization of different phases at the micrometre scale is closely related to optical or mechanical properties, manufacturing processes, functionalities in ancient times and long-term conservation. Between classic X-ray powder diffraction with a millimetre beam and transmission electron microscopy, a gap exists and structure and phase information at the micrometre scale are missing. Using a micrometre-size synchrotron X-ray beam, a hybrid approach combining both monochromatic powder micro-diffraction and Laue single-crystal micro-diffraction was deployed to obtain information from nanometre- and micrometre-size phases, respectively. Therefore providing a way to bridge the aforementioned gap, this unique methodology was applied to three different types of ancient materials that all show a strong heterogeneity. In Romanterra sigillata, the specific distribution of nanocrystalline hematite is mainly responsible for the deep-red tone of the slip, while the distribution of micrometre-size quartz in ceramic bodies reflects the change of manufacturing process between pre-sigillataand high-qualitysigillataperiods. In the second example, we investigated the modifications occurring in Neolithic and geological flints after a heating process. By separating the diffracted signal coming from the nano- and the micrometre scale, we observed a domain size increase for nanocrystalline quartz in geological flints and a relaxation of the residual strain in larger detritic quartz. Finally, through the study of a Roman iron nail, we showed that the carburation process to strengthen the steel was mainly a surface process that formed 10–20 µm size domains of single-crystal ferrite and nanocrystalline cementite.

Cu-substituted barium hexaferrite crystal growth and characterization

Magnetoplumbite type barium ferrite single crystals BaFe12−xCuxO19 with various Cu-contents in the range of x≤0.032 with edge-length of up to 12mm were obtained from carbonate flux at 1260°C. The unit cell parameters of obtained crystals increase slightly with Cu-concentration. Saturation magnetization, Curie temperature and coercivity of BaFe12−xCuxO19 drop with Cu-content, particularly above about x=0.02. The change in Hc is only insignificant.

Nanodomains and nanometer-scale disorder in multiferroic bismuth ferrite single crystals

We report on an investigation of state-of-the-art flux-grown multiferroic bismuth ferrite (BiFeO3; BFO) single crystals by transmission electron microscopy and electron diffraction. The crystals were pre-characterized by piezoresponse force microscopy, electrical resistance and superconducting quantum interference device magnetization measurements. The structurally highly perfect crystals show a ferroelectric stripe domain structure characterized by a domain width of 55nm. Inside these domains an additional contiguous nanodomain substructure occurs, consisting of 180° related domains, giving rise to satellite reflections at 121212-type positions along 〈110〉 directions in the electron diffraction pattern corresponding to a characteristic length in real space of 15.5nm. Furthermore, we present the first atomic-resolution study on the short-range order by aberration-corrected transmission electron microscopy in which all atoms including oxygen are imaged directly. By measuring the –Fe–O–Fe– atom topology, bond angles and atomic distances we derive the electrical dipole moment as well as the magnitude of the magnetic moment on the unit-cell level. The results evidence substantial atomic- to nano-scale disorder. Both the nanodomain substructure as well as the disorder should affect the subtle magnetoelectric interactions in this material and thereby impede the formation of long-range cycloidal spin ordering which up to now was considered an intrinsic feature of the magnetic properties of BiFeO3 single crystals. By Monte Carlo simulation on the basis of a state-of-the-art effective Hamiltonian we scrutinize certain aspects of the phase formation behavior in the BFO system forming the background of single-crystal growth. This study reveals a very sluggish phase evolution behavior, which should make it invariably difficult to obtain structurally fully equilibrated single crystals.

Aging and memory effect in magnetoelectric gallium ferrite single crystals

Abstract Here, we present a time and temperature dependent magnetization study to understand the spin dynamics in flux grown single crystals of gallium ferrite (GaFeO 3 ), a known magnetoelectric, ferroelectric and ferrimagnet. Results of the magnetic measurements conducted in the field-cooled (FC) and zero-field-cooled (ZFC) protocols in the heating and cooling cycles were reminiscent of a “memory” effect. Subsequent time dependent magnetic relaxation measurements carried out in ZFC mode at 30 K with an intermittent cooling to 20 K in the presence of a small field show that the magnetization in the final wait period tends to follow its initial state which was present before the cooling break taken at 20 K. These observations provide an unambiguous evidence of single crystal gallium ferrite having a spin glass like phase.

Determination of the concentration of conduction electrons in Y3Fe5O12 garnet crystals

Ferrites (garnets) are a model object of study and a promising material to be used in magneto-optical devices for data recording and processing and IR modulators. Due to the narrow ferromagnetic resonance line, optical transparency, and high elastic Q factor of ferrite single crystals, they are promising for solid-state microwave, optoelectronic, and computation devices. To ensure the optimal application of ferromagnetic materials, it is necessary to complete the following important task: develop a certification for samples with allowance for the degree of their imperfection caused by the deviation of crystals with garnet structure from stoichiometry, the competitive incorporation of process and dominant impurities, oxygen vacancies, etc.

Dielectric response and magnetoelectric coupling in single crystal gallium ferrite

Here we report the dielectric response and electric conduction behavior of magnetoelectric gallium ferrite single crystals studied using impedance analysis in time and temperature domain. The material exhibits two distinct relaxation processes: a high frequency bulk response and a low frequency interfacial boundary layer response. Calculated bulk capacitance as a function of temperature showed an anomaly at ferri- to paramagnetic transition temperature (∼ 300 K), suggestive of magneto-dielectric coupling in the material. Interestingly, we also witness an abrupt change in the activation energy at ∼ 220 K, in the vicinity of spin-glass transition temperature in GaFeO3.

Growing doped barium ferrite single crystals using the flux method

Substances exhibiting ferromagnetic properties areused in inductors, devices for recording and reproduction of sound, and information storage devices, as wellas in electronic and electrical appliances.For solving many technical problems, ferromagnets with rather high Curie temperatures (350°С) areof crucial importance. This property is inherent in barium ferrite (BaFe