Magnetic Glass Research Articles

Atomic structure and thermal behavior of (Co0.65,Fe0.35)72Ta8B20 metallic glass with excellent soft magnetic properties

New soft magnetic (Co0.65,Fe0.35)72Ta8B20 metallic glass has been synthesized and its atomic structure and thermal stability have been studied using high-energy synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Analysis of the pair correlation functions (PDF) indicates a notable shift in position of the first PDF peak to a lower distance and the decreasing the average coordination number of the first shell, compared to the (Co0.65,Fe0.35)62Ta8B30 glassy alloy, recently produced. DSC analysis shows that the new alloy has a wide supercooled liquid region of 51 K and relatively high activation energy of crystallization of about 445 kJ/mol, calculated according to the Kissinger and Ozawa methods, which demonstrates its high thermal stability. Magnetic measurements show that the new alloy exhibits outstanding soft magnetic properties, i.e., very low coercivity of 1.2 A/m, high saturation magnetization of 93.5 Am2/kg and Curie temperature of 660 K, which are significantly larger than those of (Co0.65,Fe0.35)62Ta8B30 glassy ribbon. The influence of the annealing treatment on evolution of the soft magnetic properties of the (Co0.65,Fe0.35)72Ta8B20 glassy ribbons has been investigated.

Magnetic Behavior of Soft Magnetic FeMoCuB Metallic Glass at Low Temperature

We have studied a NANOPERM-type Fe76Mo8Cu1B15 metallic glass with emphasis upon its magnetic properties at low temperatures. Temperature evolution of magnetization measured under zero-field cooling and field cooling conditions upon samples with different amounts of nanocrystalline grains have unveiled a two-phase behavior in temperature range from 50 up to about 200 K. In order to understand the correlation between the structural arrangement and resulting magnetic properties, we have employed a local probe method of 57Fe Mossbauer spectrometry performed at 300 and 4.2 K. The latter experiments were also accomplished in an external magnetic field of 6 T. Magnetically distinct regions were unveiled in the amorphous structure of the as-quenched and annealed samples. They are demonstrated by the distributions of hyperfine magnetic fields.

Multiple ferroic glasses via ordering

Structural glasses are characterized by the loss of long-range translational and rotational symmetry. In the last two decades, however, it has been discovered that materials that exhibit ferroic (ferromagnetic, ferroelectric and ferroelastic) phase transformations may also exhibit glassy behavior, in which the ferroic degrees of freedom (magnetization, polarization, strain) exhibit a loss of long-range translational symmetry. A consequence of this loss of long-range symmetry is the suppression of the ferroic phase transitions. Moreover, these unique glassy systems exhibit dynamic and thermodynamic behavior analogous to regular structural glasses. Conventionally, the onset of glassy behavior is brought about by the introduction of spatial heterogeneities, typically originating from point defects, particularly in the case of strain glasses. Here, we demonstrate, for the first time, that configurational order/disorder in a single ferromagnetic alloy (Ni45Co5Mn36.6In13.4) can be used to stabilize both strain and magnetic glasses. The control of the degree of configurational order – through simple heat treatment schedules –, and simultaneous application of stress and magnetic field enabled us to observe a Kauzmann point, that is, the collapse of the entropy difference between a crystalline and a glassy phase. Systematic investigation of the transformation behavior in this system as a function of heat treatment enabled us to observe four kinds of solid–solid phase transitions (ferromagnetic–paramagnetic, martensitic transformation, strain and magnetic glass) in a single composition. The alloy investigated can be used to further elucidate the nature of ferroic glass transitions and their coupling.

Combined use of lightweight magnetic Fe3O4-coated hollow glass spheres and electrically conductive reduced graphene oxide in an epoxy matrix for microwave absorption

Epoxy resin based lightweight composites comprising Fe3O4-coated hollow glass spheres (HGS@Fe3O4) and reduced graphene oxide (RGO) were prepared. Impedance matching condition and electromagnetic wave attenuation characteristic are used for analysis of the reflection loss (RL) performance of the composites. Compared with pure HGS@Fe3O4 and RGO composite, the −10dB absorption bandwidth and the minimum RL of the hybrid composites are enhanced. RL values less than −10dB are obtained in a wide frequency range and the corresponding bandwidth can reach up to 3.6GHz when an appropriate absorber thickness is chosen. The density of the hybrid composite is in the range of 0.57–0.72g/cm3, which is attractive candidate for a new type of lightweight microwave absorber.

Modeling Barkhausen Noise in magnetic glasses with dipole-dipole interactions

Long-ranged dipole-dipole interactions in magnetic glasses give rise to magnetic domains having labyrinthine patterns on the scale of about 1 micron. Barkhausen Noise then results from the movement of domain boundaries which is modeled by the motion of elastic membranes with random pinning. Here we propose that on the nanoscale new sources of Barkhausen Noise can arise. We propose an atomistic model of magnetic glasses in which we measure the Barkhausen Noise which results from the creation of new domains and the movement of domain boundaries on the nanoscale. The statistics of the Barkhausen Noise found in our simulations is in striking disagreement with the expectations in the literature. In fact we find exponential statistics without any power law, stressing the fact that Barkhausen Noise can belong to very different universality classes. In the present model the essence of the phenomenon is the fact that the spin response Green's function is decaying too rapidly for having sufficiently large magnetic jumps. A theory is offered in excellent agreement with the measured data without any free parameter.

The effect of magnetic field on the ferroelectric phase transition in KH2PO4 nanoparticles embedded in magnetic porous glass

We have studied the effect of an external magnetic field on the ferroelectric phase transition in KH2PO4 nanoparticles embedded in macroporous magnetic glass with an average pore diameter of 50 nm. It is established that, in a magnetic field of 10 T, the ferroelectric phase transition temperature increases by approximately 6 K.

An immobilization-free electrochemical impedance biosensor based on duplex-specific nuclease assisted target recycling for amplified detection of microRNA.

An immobilization-free electrochemical impedance biosensor for microRNA detection was developed in this work, which was based on both the duplex-specific nuclease assisted target recycling (DSNATR) and capture probes (Cps) enriched from the solution to electrode surface via magnetic beads (MBs). In the absence of miR-21, Cps cannot be hydrolyzed due to the low activity of duplex-specific nuclease (DSN) against ssDNA. Therefore, the intact Cps could be attached to the surface of magnetic glass carbon electrode (MGCE), resulting in a compact negatively charged layer as well as a large charge-transfer resistance. While in the presence of miR-21, it hybridized with Cp to form a DNA-RNA heteroduplex. Due to the considerable cleavage preference for DNA in DNA-RNA hybrids, DSN hydrolyzed the target-binding part of the Cp while liberating the intact miR-21 to hybridize with a new Cp and initiate the second cycle of hydrolysis. In this way, a single miR-21 was able to trigger the permanent hydrolysis of multiple Cps. Finally, all Cps were digested. Thus, the negatively charged layer could not be formed, resulting in a small charge-transfer resistance. By employing the above strategy, the proposed biosensor achieved ultrahigh sensitivity toward miR-21 with a detection limit of 60aM. Meanwhile, the method showed little cross-hybridization among the closely related miRNA family members even at the single-base-mismatched level. Successful attempts were made in applying the approach to detect miR-21 in human serum samples of breast cancer patients.

A novel sandwich electrochemiluminescence immunosensor for ultrasensitive detection of carbohydrate antigen 19-9 based on immobilizing luminol on Ag@BSA core/shell microspheres.

A novel sandwich-type electrochemiluminescence immunosensor based on immobilizing luminol on Ag@BSA core/shell microspheres (Ag@BSA-luminol) for ultrasensitive detection of tumor marker carbohydrate antigen 19-9 (CA19-9) has been developed. Herein, magnetic carbon nanotubes (MAGCNTs) decorated with polyethylenimine (PEI) was used to construct the base of the immunosensor. MAGCNTs with prominent electrical conductivity and high surface area could be beneficial for promoting the electron transfer and loading plenty of primary antibodies (Ab1) via glutaraldehyde (GA). Meanwhile, the magnetic property of MAGCNTs makes it easy to be attached to the surface of magnetic glass carbon electrode (MGCE) through magnetism interaction, which provides an outstanding platform for this immunosensor. Moreover, Ag@BSA microspheres with large surface area, good stability, and excellent biocompatibility were desirable candidates for effective cross-link of CA19-9 detection antibodies (Ab2). A more interesting thing was that ELISA color reaction was used as an ultrasensitive strategy for identifying Ab2 was successfully coated on Ag@BSA with the naked eye. Additionally, we immobilized the luminol on the surface of Ag@BSA to prepare the target immunosensor. Immobilization of luminol on the surface of Ag@BSA could decrease the distance between luminophores and the electrode surface, leading to great enhancement of the ECL intensity of luminol in the present of hydrogen peroxide (H2O2). Under the optimal conditions, the intensity of the ECL immunosensor increased linearly with the logarithm of CA19-9 concentration in a wide linear range from 0.0005 to 150UmL(-1) with a detection limit of 0.0002UmL(-1) (S/N=3). All the results suggested the prepared CA19-9 immunosensor displayed high sensitivity, excellent stability and good specificity. The developed method opened a new avenue to clinical bioassay.

Fabrication of Fe-based bulk metallic glass by selective laser melting: A parameter study

Abstract Soft magnetic Fe-based bulk metallic glass cylindrical specimens with a diameter of 2 mm and height of 6 mm have been successfully fabricated by selective laser melting (SLM) and the effect of scan speed v and laser power P on the microstructure, thermal stability and soft magnetic properties has been investigated. The results indicate that low v and high P lead to the formation of SLM samples with high relative densities, which can reach values of about 99.7%. This can be ascribed to the optimal energy transfer during processing at low v and high P. Structural and calorimetric studies prove that the SLM samples are fully amorphous. In addition, magnetic measurements reveal that the amorphous structure of the SLM material is identical to the parent atomized powders. Although additional work is required to remove the residual porosity and to avoid the formation of cracks during processing, the present results confirm that additive manufacturing by SLM represents an alternative processing route for the preparation of bulk metallic glass components with designed geometry having excellent magnetic softness.

Heating influence on magnetic structure in Co and Fe rich amorphous microwires

The influence of temperature on surface magnetic structure has been studied in Co- and Fe-rich magnetic glass covered microwires. The investigations have been performed using magneto-optical Kerr effect technique with a thermo-controlled system. It was found different types of domain structures depending on the temperature and the microwire composition. These types are characterised by the different domain period and the angle of the inclination of domain walls. It was established the direct correlation between surface domain structures and hysteresis loops. The coexistence of domain walls with different value of mobility has been found. It was observed original mechanism of the domain structure transformation: sharp change in the domain structure without movement of the domain walls.

Magnetic properties of novel magnetic porous glass-based multiferroic nanocomposites

In this paper we report on the first experimental studies of the magnetic and electric properties of the ferroelectric materials incorporated in magnetic porous glasses with the controlled pore size. This new material exhibits very small electrical conductivity which allows us to examine the dielectric and magnetoelectric characteristics of these porous glasses concerning magnetite. The magnetic measurements of empty porous glasses and glasses with multiferroic nanocomposites demonstrate the Verwey transition in magnetite. Ferroelectric phase transitions were observed together with hysteresis loops as irrefutable proof of the ferroelectricity in multiferroic nanocomposites based on magnetic porous glasses. The observed exceptional electrical properties show large potential of this novel group of multiferroics for modern applications.

Multiple magnetic transitions, dynamical magnetic liquid and magnetic glass in La1−x−yPryCaxMnO3 (x≈0.42, y≈0.40) thin films: A thickness dependent study

The influence of substrate induced strain and its relaxation on the evolution of the multiple magnetic transitions and ensuing modifications in the degree of phase separation, the nature of the dynamical magnetic liquid, the randomly frozen glass and insulator–metal transitions have been investigated in single crystalline La1−x−yPryCaxMnO3 (x≈0.42, y≈0.40) in t~20–140nm thick films deposited on LaAlO3 (001) substrates. The ferromagnetic (FM) transition temperature (TC) first decreases as the film thickness is increased from t~20nm to t~60nm and then increases with increasing film thickness. In contrast the charge ordering (CO), antiferromagnetic (AFM) and glass transition temperatures shift towards higher values with increasing film thickness. The field cooled cooling (FCC) and field cooled warming (FCW) magnetization (M–T) of films having t≥60nm shows pronounced hysteresis and ΔTC=TCFCW−TCFCC decreases concomitantly from 46K to 35K as the thickness increases from ~60 to ~140nm. The thinnest film shows insulator to metal transitions (IMT) only at magnetic field H>40kOe. Films with t≥TC show sharp hysteretic IMT, with ΔTIM=TIMW−TIMC decreasing from ~70K to ~50K as the thickness increases from ~60nm to ~140nm. Such strong hysteresis is a characteristic of first order phase transition and also a signature of magnetic liquid like phase created by the magnetic frustration created by the delicate balance between FM and AFM/CO phases. The H induced AFM/CO to FM transition reduces ΔTIM and at higher fields the phase transition appears akin to the second order. The observed difference in the magnetic and transport properties have been explained in terms of the substrate induced strain at lower film thickness and its relaxation at higher thickness.

Supercooled spin liquid state in the frustrated pyrochlore Dy2Ti2O7

A "supercooled" liquid develops when a fluid does not crystallize upon cooling below its ordering temperature. Instead, the microscopic relaxation times diverge so rapidly that, upon further cooling, equilibration eventually becomes impossible and glass formation occurs. Classic supercooled liquids exhibit specific identifiers including microscopic relaxation times diverging on a Vogel-Tammann-Fulcher (VTF) trajectory, a Havriliak-Negami (HN) form for the dielectric function ε(ω, T), and a general Kohlrausch-Williams-Watts (KWW) form for time-domain relaxation. Recently, the pyrochlore Dy2Ti2O7 has become of interest because its frustrated magnetic interactions may, in theory, lead to highly exotic magnetic fluids. However, its true magnetic state at low temperatures has proven very difficult to identify unambiguously. Here, we introduce high precision, boundary-free magnetization transport techniques based upon toroidal geometries and gain an improved understanding of the time- and frequency-dependent magnetization dynamics of Dy2Ti2O7. We demonstrate a virtually universal HN form for the magnetic susceptibility χ (ω, T), a general KWW form for the realtime magnetic relaxation, and a divergence of the microscopic magnetic relaxation rates with the VTF trajectory. Low-temperature Dy2Ti2O7 therefore exhibits the characteristics of a supercooled magnetic liquid. One implication is that this translationally invariant lattice of strongly correlated spins may be evolving toward an unprecedented magnetic glass state, perhaps due to many-body localization of spin.

Effect of the external field on the soft magnetic properties and microstructure of directly cast Fe75P8.7B5C7Si4.3 nanocrystalline sheets

A new method to fabricate soft magnetic bulk metallic glasses (BMGs) by an injection casting with applying external magnetic field during solidification has been developed. The effect of applying magnetic fields (Ha) on soft magnetic properties and microstructure of Fe75P8.7B5C7Si4.3 alloy sheets with dimension of t × 4 mm × 15 mm (t = 1–3 mm) have been studied. The microstructure shows that the fully amorphous is attained by the applying magnetic field even at the core region of the thicker sheets with t = 3 mm. All studied sheets exhibit similar saturation magnetization of 1.23–1.25 T, but the coercivity and resistivity are strongly dependent on the thickness t and the strength of magnetic field Ha, where Hc increases with t, the slope of Hc versus t decreases with the increase of Ha, and the resistivity increases with the increase of Ha. The changes of coercivity and resistivity are strongly related to the fully amorphous induced by Ha. The external magnetic field has significant improvement in glass forming ability, and thus coercivity and resistivity for the studied sheet, especially for larger t = 3 mm. This study suggests that applying a magnetic field during the casting process provides a useful way to produce high-performance magnetically soft Fe-based BMGs.

Synthesis, characterization and in vitro study of magnetic biphasic calcium sulfate-bioactive glass

Calcium sulfate-bioactive glass (CSBG) composites doped with 5, 10 and 20 mol% Fe were synthesized using quick alkali sol-gel method. X-ray diffraction (XRD) data of samples heated at 700 °C revealed the presence of anhydrite, while field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) characterization confirmed the formation of nano-sized CSBGs. The UV-vis studies confirmed that the main iron species in 5% Fe and 10% Fe doped CSBGs were tetrahedral Fe(III) whereas that in 20% Fe doped CSBG were extra-framework FeOx oligomers or iron oxide phases. Measurement of magnetic properties of the samples by vibrating sample magnetometer (VSM) showed very narrow hysteresis loop with zero coercivity and remanence for 10% Fe and 20% Fe doped CSBG, indicating that they are superparamagnetic in nature. All samples induced the formation of apatite layer with Ca/P ratio close to the stoichiometric HA in simulated body fluid (SBF) assessment.

High-pressure synthesis, crystal structures, and magnetic properties of 5d double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6.

Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ∼1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ∼19 K and an antiferromagnetic (AFM) transition at ∼110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices.

Production of Magnetic Alkali-Borosilicate Glasses by Induction Melting

The equipment and procedure for fabrication of magnetic alkali-borosilicate glasses by the method of induction melting are described. Field dependencies of the specific magnetization are presented and the values of the coercive fields (about 100 Gs) of the magnetic glasses are determined.

Current sensors using Fe–B–Nd–Nb magnetic metallic glass micro-cantilevers

We report on the development of MEMS current sensors composed of Fe67.5B22.5Nd6.3Nb3.7 (FBNN) magnetic metallic glass thin films. These current sensors are based on free-standing cantilever structures that benefit from the superior mechanical properties of the metallic glass, such as high fracture toughness and high yield strength. The resonant frequency of the proposed FBNN cantilever was 3.85kHz in the fundamental flexure mode when the length, width and thickness of the cantilever were 750μm, 150μm and 3μm, respectively. A feed wire with a diameter of 500μm was placed close to the FBNN cantilever, and a downshift in the resonance peak was observed when the current intensity through the feed wire increased. The sensitivity of this frequency shift to the current intensity was 5.0√Hz/A when the distance between the cantilever and the wire was 500μm.

Room temperature nonlinear magnetoelectric effect in lead-free and Nb-doped AlFeO3 compositions

It is still a challenging problem to obtain technologically useful materials displaying strong magnetoelectric coupling at room temperature. In the search for new effects and materials to achieve this kind of coupling, a nonlinear magnetoelectric effect was proposed in the magnetically disordered relaxor ferroelectric materials. In this context, the aluminum iron oxide (AlFeO3), a room temperature ferroelectric relaxor and magnetic spin glass compound, emerges as an attractive lead-free magnetoelectric material along with nonlinear magnetoelectric effects. In this work, static, dynamic, and temperature dependent ferroic and magnetoelectric properties in lead-free AlFeO3 and 2 at. % Nb-doped AlFeO3 multiferroic magnetoelectric compositions are studied. Pyroelectric and magnetic measurements show changes in ferroelectric and magnetic states close to each other (∼200 K). The magnetoelectric coefficient behavior as a function of Hbias suggests a room temperature nonlinear magnetoelectric coupling in both single-phase and Nb-doped AlFeO3-based ceramic compositions.

Fragmentation of Co-Fe-Ta-B Soft Magnetic Amorphous Alloy

The main limitation of high-strength Co-based bulk metallic glasses for their application as structural materials is the large brittleness. Spontaneously emerging cracks in the alloy degrade the magnetic properties. We analyzed the failure characteristics of Co43Fe20Ta5.5B31.5 bulk soft magnetic metallic glass deformed in the compression at room temperature and the low strain rate. Under loading the amorphous structure stores high elastic energy. During the failure this energy is released and the alloy breaks into small particles or powder exhibiting a fragmentation mode.