Ferromagnetic Glass Research Articles

Formation of New Glass-Ceramic Materials with Controllable Dielectric and Magnetic Properties

Materials with strong susceptibility with respect to the electromagnetic field, namely, ferroelectric (FE) and ferromagnetic (FM) materials are of great interest for modern electronics. On the basis of ferroelectrics, devices such as varicades, delay lines, phase shifters, etc. are being actively developed. Ferromagnets (primarily ferrites) serve as the basis for directional couplers, circulators, valves, filters, phased antenna arrays, etc. Today, the most common method of creating functional composites, combining dielectric and magnetic properties, is the introduction of classical ferroelectrics, such as triglycine sulfate, Siegnette salt (KNaC4H4O6∙4H2O), sodium nitrite, etc. in iron-containing matrices. The relevance of this approach is due to the fact that when a ferroelectric is introduced into the FM matrix, it becomes possible to create composite multiferroic materials with two types of ordering (electric and magnetic). In this paper, we study the possibilities of creating glass-ceramic multiferroic materials based on Siegnette salt and barium titanate, introduced in the pore space of ferromagnetic glass, formed by ion exchange between alkaline glass cations and salt melt. For obtaining porous glass-ceramic materials by the method of ion exchange, potassium iron-containing silicate glasses are used in the work. 15K2O·20Fe2O3·55SiO2, mol. % (KFeSi).

Magnetic excitations in ferromagnetic glasses

We have studied theoretically (including computer simulations) dynamical magnetic properties of aggregates of ferromagnetic amorphous nanogranules in the presence of direct exchange between the neighboring granules and random anisotropy fields. It was shown that in such structures there still exist delocalized magnetic excitations similar to magnons in the bulk materials, although at much lower frequencies. The excitations at high frequencies are localized within the corresponding granules. The details of spectrum of these excitations (including structural factors) are discussed.

Preparation and properties of ferromagnetic glass ceramics and glass fibers based on the composition of SiO2-B2O3-Fe2O3-SrO

The ferromagnetic glass ceramics in the system SiO2-B2O3-Fe2O3-SrO were prepared via four different fabrication methods, i.e., fiber-drawing, melt-quenching, natural-cooling, and annealing, without performing any nucleation and crystallization heat treatments. The influences of chemical composition and fabrication method on the spontaneous crystallization of magnetite were investigated by X-ray diffraction, scanning and transmission electron microscopy. The X-ray diffraction patterns show the presence of nanometric magnetite crystals in the glass matrix, and the increasing boron oxide can promote the spontaneous crystallization of magnetite. The estimated size of crystallized magnetite varies between 12 and 50nm. The magnetic properties of the glass ceramics derived from the four fabrication methods were analyzed using a Vibrating sample magnetometer (VSM), Agilent HP8722ES vector network analyzer and Mössbauer spectra. We find that both the saturation magnetization (MS) and coercivity (Hjc) depend on the chemical composition and fabrication method. The calorimetric measurements were carried out using Orton Standard Dilatometers.

Bioactivity of Fe2O3-CaO-SiO2 glass ceramics modified through the addition of P2O5 and TiO2

The bioactivity of ferromagnetic glass ceramics is one key factor affecting the success of hyperthermia treatments. In order to investigate the effect of the addition of a nucleating agent on the bioactivity of the resulting glass ceramics, two different nucleating agents were used for the fabrication of Fe2O3-CaO-SiO2 glass ceramics, and their short-term and long-term effects on the cytotoxicity of human fetal normal colonic mucosa cells were evaluated. The results show that P2O5 promotes the formation of an apatite-like phase on the surface of Fe2O3-CaO-SiO2 glass ceramics immersed in simulated body fluid. While TiO2 had some adverse effect on the cell viability, P2O5 had little effect on the cell viability over a certain concentration range. In this paper, the prepared Fe2O3-CaO-SiO2 glass ceramics with P2O5 added as nucleating agent are demonstrated to exhibit a good bioactivity and low cytotoxicity, which suggests good application prospects in the field of hyperthermia.

Ferromagnetic glass ceramics and glass fibers based on the composition of SiO2-CaO-Al2O3-B2O3-Fe2O3 glass system

Ferromagnetic glass-ceramics and glass fibers were obtained by the melt-method from the glass system SiO2-CaO-Al2O3-B2O3-Fe2O3 without performing any nucleation and crystallization heat treatments. Glass-ceramics and glass fibers were characterized by x-ray diffraction, scanning and transmission electron microscopy, magnetic measurements, and thermal expansion instrument. The influence of alumina content on the spontaneous crystallization of magnetite, magnetism properties and thermal expansion performances in glass were investigated. We examined the crystallization behavior of the glasses and found that the spontaneous crystallization capacity of magnetite and magnetism properties in base glass increases with increasing the content of alumina. The ferromagnetic glass fibers containing magnetite nano-crystals are also obtained.

Effect of zirconium substitution on the dielectric and magnetic properties of YMn0.8Fe0.2O3 multiferroic ceramics

Dielectric and magnetic properties of Zr substituted YMn0.8Fe0.2O3 ceramics were investigated in this work. Single phase in space group of P63cm and homogeneous microstructure were identified in the Y0.95Zr0.05Mn0.8Fe0.2O3 ceramics, while small amount of secondary phase located at the grain boundary was detected in the Y0.9Zr0.1Mn0.8Fe0.2O3 ceramics. Compared with YMn0.8Fe0.2O3, the significantly reduced room-temperature dielectric loss was obtained in the Y0.95Zr0.05Mn0.8Fe0.2O3 ceramics, and this improvement has great scientific significance for the potential applications of multiferroic materials. The XPS analysis results confirmed that Fe2+ ions disappeared and the Mn2+ content was obviously decreased, when 5 at.% Zr was introduced to the Y sites of YMn0.8Fe0.2O3. The reduced Mn2+ and Fe2+ ions contents led to the obviously reduced dielectric loss of Y0.95Zr0.05Mn0.8Fe0.2O3 ceramics. The existence of enhanced weak ferromagnetic properties and cluster glass state behavior at low temperature was detected in Zr substituted YMn0.8Fe0.2O3 ceramics. The present work suggests a promising YMnO3 based multiferroic ceramics with reduced room-temperature dielectric loss.

Low power loss in Fe65.5Cr4Mo4Ga4P12B5.5C5 bulk metallic glasses

Power loss – one of the important application-oriented magnetic properties of ferromagnetic metallic glasses – has been well studied in glassy ribbons rather than bulk metallic glasses. This paper studies the influence of frequency, induction, annealing, and specimen thickness on the total power loss – which is divided into hysteresis loss, classical eddy current loss, and excess eddy current loss – of bulk ferromagnetic Fe65.5Cr4Mo4Ga4P12B5.5C5 glasses. The total power loss of bulk glasses increases with frequency and peak induction and follows a power relation, similar to what has been observed in glassy ribbons. Annealing decreases both the hysteresis loss and the classical eddy current loss, resulting in a lower total power loss. The ratio of excess eddy current loss to classical eddy current loss deceases with increasing specimen thickness. The excess eddy current loss is negligible for our thickest glass and comparable to the classical eddy current loss for our thinner glasses. In contrast, the excess eddy current loss is often at least one to two orders of magnitude greater than the classical eddy current loss in glassy ribbons. The low total power loss achieved in bulk ferromagnetic glasses should be beneficial to their practical applications in energy conversion devices.

Effects of metalloids on the thermal stability and glass forming ability of bulk ferromagnetic metallic glasses

We prepared three types of bulk ferromagnetic glasses, Fe–Mo–P–C, Fe–Mo–Ga–P–B–C, and Fe–(Co, Sb, Cr, Mo, Ga)–P–B–C by a flux-melting and water-quenching technique. We systematically changed the content of both alloying metals and metalloids to improve the glass-forming ability (GFA) and thermal stability – the difference between crystallization temperature Tx and glass transition temperature Tg – of bulk ferromagnetic glasses. One of our flux-melted ferromagnetic alloys with optimized compositions has a critical cooling rate on the order of ∼10Ks−1, suggesting that the flux treatments play an important role in improving the GFA. Tuning the thermal stability of supercooled liquid by modifying the content of alloying metalloids is more effective than by modifying the content of alloying metals. Adding 1at.% alloying metalloids and metals can increase Tx–Tg by ∼20K and 4K, respectively. We found that upon increasing the content of alloying metalloids, Tx–Tg increases and reaches a maximum where the GFA is highest. After Tx–Tg reaches a maximum, a further increase in the content of alloying metalloids lowers the GFA whereas Tx–Tg may either increase or decrease. Bulk ferromagnetic glasses can only be formed by modifying the content of metalloids within a narrow range, ∼2–6at.%, in our alloy systems. Our experimental results suggest that optimizing the content of metalloids is a powerful tool for improving the GFA and thermal stability of bulk metallic glasses.

Utilization of iron oxide bearing pellets waste for preparing hard and soft ferromagnetic glass ceramics

About 8% of the imported iron oxide pellets burdens to Egypt are wasted. In this paper, broken pellets waste (BPW) is used as raw material for the preparation of hard magnetic glass ceramics (HMGC) as well as soft magnetic glass ceramics (SMGC). About 54 wt% and 37 wt% of BPW are used to prepare SMGC and HMGC, respectively. Differential thermal analysis (DTA) reveals two broad exothermic peaks for HMGC at 591 °C and 697 °C, whereas one exothermic peak at 820 °C is detected for SMGC. X-ray diffraction (XRD) shows the crystallization of hematite as the sol phase in BPW, and meanwhile, Zn-ferrite and Ba-hexaferrite are identified in SMGC and HMGC, respectively. Transmission electron microscopy (TEM) reveals the crystallization of nanosize particles of ∼20 nm for SMGC and ∼12 nm for HMGC. Vibrating scanning magnetometer (VSM) reveals an increase in saturation magnetization from ∼1 emu/g for BPW to ∼77 emu/g for SMGC and 21 emu/g for HMGC.

Investigation of the magnetostriction coefficient of amorphous ferromagnetic glass coated microwires

We measured the magnetostriction coefficient using small angle magnetization rotation method in amorphous ferromagnetic glass-coated Fe, Co, FeCo, and FeCoNi-based microwires. It was found that when the metallic nucleus of the microwire has a high magnetostriction—of the order (10–30) × 10−6 for FeCo-based microwires, the changing of diameters ratio, and hence, the magnitude and distribution of mechanical stresses have no significant effect on the value of the magnetostriction coefficient. In the case of nearly zero magnetostrictive FeCoNi-based microwires, increasing of the ρ−ratio leads to decreasing in the absolute value of the magnetostriction coefficient.

Characterization of Fe<sub>2</sub>O<sub>3</sub>-CaO-SiO<sub>2</sub> Glass Ceramics Prepared by Sol-Gel

Ferromagnetic glass ceramics with magnetism and biological activity could be used for magnetic induction hyperthermia. In this study Fe2O3-CaO-SiO2glass-ceramics were prepared by sol-gel method. The sample was characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). The results showed that the major phases of the sample are wollastonite and magnetite and the crystallization activation energy of sample is 189.3KJ/mol, which would provide a theoretical basis for the establishment of the optimum process conditions of heat treatment technology.

Analytical estimates of the locations of phase transition points in the ground state for the bimodal Ising spin glass model in two dimensions

We analytically estimate the locations of phase transition points in the ground state for the $\pm J$ random bond Ising model with asymmetric bond distributions on the square lattice. We propose and study the percolation transitions for two types of bond shared by two non-frustrated plaquettes. The present method indirectly treats the sizes of clusters of correlated spins for the ferromagnetic and spin glass orders. We find two transition points. The first transition point is the phase transition point for the ferromagnetic order, and the location is obtained as $p_c^{(1)} \approx 0.895 \, 399 \, 54$ as the solution of $[p^2 + 3 (1-p)^2 ]^2 \, p^3 - \frac{1}{2} = 0$. The second transition point is the phase transition point for the spin glass order, and the location is obtained as $p_c^{(2)} = \frac{1}{4} [2 + \sqrt{2 (\sqrt{5} - 1)}] \approx 0.893 \, 075 \, 69$. Here, $p$ is the ferromagnetic bond concentration, and $1 - p$ is the antiferromagnetic bond concentration. The obtained locations are reasonably close to the previously estimated locations. This study suggests the presence of the intermediate phase between $p_c^{(1)}$ and $p_c^{(2)}$; however, since the present method produces remarkable values but has no mathematical proof for accuracy yet, no conclusions are drawn in this article about the presence of the intermediate phase.

Effect of La2O3, CoO, Cr2O3 and MoO3 nucleating agents on crystallization behavior and magnetic properties of ferromagnetic glass–ceramic in the system Fe2O3·CaO·ZnO·SiO2

Preparation and characterization of ferromagnetic glass ceramic in the system Fe2O3·CaO·ZnO·SiO2 with different nucleating agents was studied. The effect of La2O3, CoO, Cr2O3 and MoO3 as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of crystallization and microstructure of the samples. XRD analysis for as prepared samples revealed the crystallization of single magnetite phase. Heat treatment at 900°C/2h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside magnetite. TEM revealed crystallization of crystallite size in the range 50–100nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20kG.

Preparation and Characterization of SrO-Al2O3-Fe2O3-B2O3 System Nano-Ferrimagnetic Glass-Ceramics

Based on the SrO-Al2O3-Fe2O3-B2O3 system, the nano-ferrimagnetic glass ceramics has been prepared through heat treating the melted glass. Using the aqueous solution solvent evaporation and melt method, we firstly obtained the molecular-scale homogenously mixed compound. And thus the glass specimen was produced by naturally cooling the batch melts. The crystallization of the glass systems with diffirent component has been systematically investigated by using X-ray diffraction (XRD), Thermo gravimetric (TG), Differential Thermal Analysis (DTA) as well as Vibrating Sample Magnetometer (VSM). It is found that Fe3O4 crystal precipitated during naturally cooling the melt from 1500°C to anneal temperature. Moreover, the nano-ferromagnetic glass ceramics with the main crystal phase of SrFe12O19 was obtained after heat-treated at 865°C for 2 hours. The size of crystal was 20-50nm. The magnetic properties of the obtained ferromagnetic glass ceramics indicated that the saturation magnetization and the intrinsic coercivity were 32A•m2/kg and 236KA/m, respectively.

Magnetic properties of nanoparticles glass–ceramic rich with copper ions

The current study aimed at the assessment of CuO gradual addition on the crystallization behavior and magnetic properties of ferromagnetic glass ceramic in the system Fe 2O 3·CaO·ZnO·SiO 2. Ferromagnetic glass–ceramics with a high quantity of magnetite were designed to be crystallized in the system Fe 2O 3·CaO·ZnO·SiO 2. The influences of gradual addition of CuO and melting temperature on the sequence of crystallization and magnetic properties were studied. The X-ray diffraction patterns showed the presence of nanometric magnetite crystals in a glassy matrix after direct cooling from the melt without any additional heat treatments. Increasing the melting temperature resulted in an increase in the magnetite crystallization. The addition of up to 20 g CuO/100 g batch composition revealed a decreasing effects in both endo- and exothermic values, whereas, the same values were inversely increased with increasing the CuO addition to 30 g. In general, increasing the CuO amounts greatly enhanced the crystallization of magnetite. A significant amount of delaffosite (CuFeO 2) was unexpectedly detected and increased by increasing both the added amount of CuO and the treatment temperature. The XRD results detected some traces of cuprite (Cu 2O) in the samples of high CuO content. The TEM results reflected the precipitation of nano-magnetite crystals in the 2–10 nm size range. Magnetic hysteresis cycles were analyzed using a vibrating sample magnetometer with a maximum applied field of 20 kOe at room temperature in quasi-static conditions. From the obtained hysteresis loops, the saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) were determined.

Phase field theory of proper displacive phase transformations: Structural anisotropy and directional flexibility, a vector model, and the transformation kinetics

A phase field theory of proper displacive transformations is developed to address the microstructure evolution and its response to applied fields in decomposing and martensitic systems. The theory is based on the explicit equation for the non-equilibrium free energy function of the transformation strain obtained by a consistent separation of the total strain into transformation and elastic strains. The transformation strain is considered to be a relaxing long-range order parameter evolving in accordance with the system energetics rather than as a fixed material constant used in the conventional Eshelby theory of coherent inclusions. The elastic strain is defined as a coherency strain recovering the crystal lattice compatibility. The obtained free energy function of the transformation strain leads to the concepts of structural anisotropy and directional flexibility of low symmetry phases. The formulated vector model of displacive transformation makes apparent a similarity between proper displacive transformation and ferromagnetic/ferroelectric transformation and, in particular, a similarity between the structural anisotropy and magnetic/polar anisotropy of ferromagnetic/ferroelectric materials. It even predicts the feasibility of a glass-like structural state with unlimited directional flexibility of the transformation strain that is conceptually similar to a ferromagnetic glass. The thermodynamics of the equilibrium between low symmetry phases and the thermodynamic conditions leading to the formation of adaptive states are formulated.

Ferromagnetic glass on the base of aggregates of Ni amorphous nanogranules

We have studied theoretically (including computer simulations) magnetic properties of aggregates of ferromagnetic amorphous nanogranules in the presence of direct exchange between the neighboring granules and random anisotropy fields. We show that such a system can be considered as ferromagnetic glass. We demonstrate (basing on analytical considerations as well as on the results of numerical simulations) that the system is decomposed to clusters or domains with nearly collinear orientation of magnetization. The size of the domains depends on the ratio of the exchange interaction and random anisotropy. For quasi-2D structures we predict that the dipole–dipole interactions between the granules lead to a formation of magnetic vortices. Moreover, the computer simulations also reproduce the puzzling increase of the thermoremanent magnetization observed experimentally, which is expected to be a result of a temperature-dependent decrease in the anisotropy (or a temperature-dependent increase in the exchange). We also consider the structures with weak intergranular exchange and show that they are characterized by the presence of two critical temperatures.

Nano particles of iron oxides in SiO2 glass prepared by ion implantation

Quartz (SiO2) glass was implanted with 5 × 1016 57Fe ions/cm2 at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mossbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO2 glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe3+ and Fe2+ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe2+ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic e-Fe2O3 precipitated in SiO2 matrix. Small amounts of α-Fe2O3 were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible.

Magnetotransport properties of a percolating network of magnetite crystals embedded in a glass-ceramic matrix

Electrical resistance, magnetization, and magnetoresistance have been measured as functions of temperature from 50 to 300 K on three ferromagnetic glass ceramics containing different magnetite crystals by preparing conditions and crystal morphology. Magnetite crystals form a percolating network for electrons with weak links at crystal-crystal contact points. All samples exhibit a broadened Verwey transition, peaked at temperatures lower than measured in bulk stoichiometric magnetite. The negative magnetoresistance ratio increases in absolute value with sample cooling from RT down to the Verwey temperature and decreases on further cooling. This behavior indicates that electron transfer between magnetite crystals is achieved through spin-dependent and spin-independent channels acting in parallel. Magnetic correlation states for spins at contact points between magnetite crystals are studied by plotting the magnetoresistance as a function of reduced magnetization. The transition from activated hopping to variable range hopping affects the magnetoresistance versus magnetization curves.

Preparation and characterization of some ferromagnetic glass–ceramics contains high quantity of magnetite

Ferrimagnetic glass–ceramics are promising candidates for magnetic induction hyperthermia, which is one form of inducing deep-regional hyperthermia, by using a magnetic field. The aim of this work was to study the effect of increasing the amount of crystallized magnetite on the magnetic properties of glass–ceramic samples. Two different ferrimagnetic glass–ceramics with the composition based on wollastonite or hardystonite with high quantity (∼60%) of magnetite were prepared by melting the starting materials at 1450 °C for 2 h. The influences of chemical composition, amount of crystallized magnetite and microstructure of ferrimagnetic glass–ceramics on magnetic properties of ferromagnetic glass–ceramics were investigated using differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The X-ray diffraction patterns show the presence of nanometric magnetite crystals in a glassy matrix after cooling from melting temperature. The amount of crystallized magnetite varies as a function of the chemical composition and heat treatment schedule. The presence of ZnO in the glass–ceramics was found to decrease the viscosity and so cases higher degree of mobility of ions leading to higher degree of crystallinity. The higher heat treatment parameters and so the lower viscosity of the glass containing ZnO are assumed to allow the magnetite to grow to larger crystallite size. Glass transition temperature and thermal stability were found to be functions of chemical composition. Magnetic hysteresis cycles were analyzed using a vibrating sample magnetometer (VSM) with a maximum applied field of 15 kOe at room temperature in quasi-static conditions. From the obtained hysteresis loops, the saturation magnetization (Ms), remanance magnetization (Mr) and coercivity (Hc) were determined. The results showed that these materials are expected to be useful in the localised treatment of cancer.