Magnetic Glass Research Articles

Track-etch membranes enabled nano-/microtechnology: A review

The art and science of fabricating structures with nano-/micrometric dimensions as well as precision is of the immense concern to any one investigating into nano-/microtechnology. The synergetic support of radiation and its potential in combining radiation effects with nano-/micromaterials has been recognized from the very early stages of nano-science research. In the myriad of applications and uses of nano-/microstructures, and nano particles in particular, from filtration, fabrication of biosensors, a chemical catalysis, magnetic structures, nano-electronics, MEMS, mechano-chemical conversion, quantum computing etc to name a few, radiation can play a significant role. One such potential application is track-etch membranes- a spin-off from the matter–radiation interaction. In the recent years, there has been a tremendous leap in the potential applications of metallic as well as non-metallic nano-/microstructures and materials. Nanotechnology has initiated a big hop and appears to be all set for bringing in revolution in the development and advancement of techniques involved in the synthesis and fabrication of sensors and devices. The conventional techniques for fabrication of very low dimensional wires – say quantum wires, include wet chemistry, electron beam lithography, focused ion beam techniques and atomic-beam lithography but for certain drawbacks and problems mentioned further. That has shown the ways for adopting newer alternative approaches which are relatively inexpensive, easier to handle and synergistically adorned with high efficacy. It is now well known that size of the devices and components dictate many unusual traits where quantum effects become more predominant. Quasi-one-dimensional nanostructures and materials like nanowires, fibres, tubules etc, having high aspect ratio would provide unusual and uncommon properties. Some properties like strength and hardness enhancement, dramatic changes in electrical conduction, field-ion-emission through tunneling phenomenon, optical, magnetic, and chemical and other important functional attributes etc are found to be enhanced when the size reduction comes into play. This review article addresses the art and science of specific technique-the “Template Synthesis”(TS) used as a route in the development of nano-/micromaterials and structures involving metals, non-metals, semiconductors, magnetic multilayered nanowires, conducting polymers, glasses, nanotubules, wires and whiskers etc. The recent past has witnessed keen interest being generated on the use of innovative technologies like TS in the production of nanomaterials' fabrication reported from various authors and from our lab. The strategy for embedding matter of interest within the etched pores or channels in the template is the material's placement through some suitable mechanism at the desired places viz., pores.

Large relative cooling power of Gd 52.5Co 16.5Al 31 magnetic bulk metallic glass

The magnetocaloric effect and thermal stability have been investigated on the new bulk metallic glass (BMG) Gd 52.5Co 16.5Al 31 alloy. The extent of supercooled liquid region is 70 K, which is wider than that of any other Gd–Co–Al ternary BMGs. The magnetic entropy change (Δ S M ) and relative cooling power ( RCP) of 9.8 J/kg K and 9.1×10 2 J/kg are obtained, respectively, under a field change of 5 T. The large Δ S M and RCP values make Gd 52.5Co 16.5Al 31 BMG attractive potential candidate for the magnetic refrigeration application.

Excess specific heat and evidence of zero-point entropy in magnetic glassy state of half-doped manganites

We show that specific heat ${C}_{p}$ has non-Debye behavior for glassy states in half-doped manganites. Irrespective of the magnetic order or electronic states, these magnetic glasses have higher ${C}_{p}$ compared to their equilibrium counterparts. The excess ${C}_{p}$ contributed by the glassy state varies linearly with temperature similar to conventional glasses indicating tunneling in the two-level systems. These glassy states show signature of zero-point entropy. Magnetic glasses can be produced simply by different field cooling protocols and may be considered ideal magnetic counterpart of the conventional glass.

Persistent photoinduced magnetization and oxygen non-stoichiometry inLa0.9Ca0.1MnO3 films

The influence of thermal annealings onLa0.9Ca0.1MnO3 (LCMO) films in oxygen and in vacuum with low hole doping is investigated in thephase separation region where competition between AFM and FM phases is high.Measurements by x-ray diffractometry, atomic force microscopy and magnetometryreveal changes in the lattice parameters and magnetic properties of the films,depending on the oxygen content. All films show magnetic cluster glass properties withsimilar freezing temperatures of around 45 K. Clearly the highest increase of themagnetization is observed in the films annealed in vacuum. We attribute this effect totrapping of unpaired electrons at oxygen vacancies where they can form rigidself-trapped magnetic polarons in potential wells of local moments. As a resultlong-range spin distortions with local ferromagnetic order may be realized. Inconformity with these results, photoinduced persistent magnetization showing differentmechanisms of generation, depending on the method of thermal annealing, is observed.

Low-temperature phase segregation in La2∕3Ba1∕3MnO3: Manifestation of nonequilibrium thermodynamics

Thermodynamic characteristics of the perovskite-like compound La2∕3Ba1∕3MnO3, exhibiting a structural phase transformation of the martensitic type with a characteristic temperature Ts≈200K, are studied in the temperature range 2–340K. Step-like hysteretic temperature behavior of the effective heat capacity is revealed at 150–250K and attributed to the discrete kinetics and a latent heat of the martensitic transformation. The magnetic subsystem is found to exhibit a magnetic glass state below 220K and temperature hysteresis of the magnetic susceptibility clearly pronounced in the 40–100K and 180–230K regions. The Debye and Einstein temperatures, θD=230K and θE=500K, respectively, derived from the experimental Debye–Waller factors for the La∕Ba, Mn, and O sublattices, are used to refine contributions from the structural and magnetic transformations to the heat capacity and to reveal thermodynamically nonequilibrium states.

Cluster spin-glass state and Kondo behavior in Sm-based bulk metallic glasses

We investigate the magnetization and electrical transport properties of Sm-based ternary magnetic bulk metallic glasses at low temperatures. A cluster spin-glass phase is evidenced below Tf∼25 K, which is probably ascribed to competition among the multifold magnetic interactions and intrinsic structural inhomogeneity, and further demonstrated by the magnetic hysteresis under field-cooling conditions. It is shown that the short-range magnetic clusters play as scattering centers for conductive electrons and result in a Kondo-like transport behavior in highly spin disordered Sm50Al25Co25 at low temperature.

Separation of PCR-ready DNA from dairy products using magnetic hydrophilic microspheres and poly(ethylene glycol)–NaCl water solutions

Carboxyl group-containing magnetic nonporous poly(2-hydroxyethyl methacrylate- co-glycidyl methacrylate) (P(HEMA- co-GMA)) and magnetic glass microspheres were used for the isolation of bacterial DNA. P(HEMA- co-GMA) microspheres were prepared by the dispersion polymerization in toluene/2-methylpropan-1-ol mixture in the presence of magnetite nanoparticles obtained by coprecipitation of Fe(II) and Fe(III) salts with ammonium hydroxide. Carboxyl groups were then introduced by oxidation of the microspheres with potassium permanganate. The most extensive DNA recovery was achieved at PEG 6000 concentrations of 12% or 16% and 2 M NaCl. The method proposed was used for bacterial DNA isolation from different dairy products containing Bifidobacterium and Lactobacillus cells. The presence of target DNA and the quality of isolated DNA were checked by polymerase chain reaction (PCR) amplification with specific primers.

Contrasting the magnetic response between a magnetic glass and a reentrant spin glass

Magnetic glass is a recently identified phenomenon in various classes of magnetic systems undergoing a first-order magnetic phase transition. We shall highlight here a few experimentally determined characteristics of magnetic glass and the relevant set of experiments, which will enable to distinguish a magnetic glass unequivocally from the well-known phenomena of spin glass and reentrant spin glass.

Structural Changes in Deformed Soft Magnetic Ni-Based Metallic Glass

The effects of intensive plastic deformation of the soft magnetic metallic glass Ni Si 13 on the structural relaxation were examined. The enthalpy changes studied by differential scanning calorimetry revealed that the intensive plastic deformation was associated with the partial structural relaxation of the amorphous structure.

Revealing novel quantum phases in quantum antiferromagnets on random lattices

Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by applying a magnetic field or pressure on the sample. When doping the system with non-magnetic impurities, novel inhomogeneous phases emerge from the interplay between geometric randomness and quantum fluctuations. In this paper we review our recent work on quantum phase transitions and novel quantum phases realized in disordered quantum magnets. The system inhomogeneity is found to strongly affect phase transitions by changing their universality class, giving the transition a novel, quantum percolative nature. Such transitions connect conventionally ordered phases to unconventional, quantum disordered ones - quantum Griffiths phases, magnetic Bose glass phases - exhibiting gapless spectra associated with low-energy localized excitations.

Magnetic power losses in [(Fe1-xCox)75B20Si5]93Nb4Y3 (x = 0, 0.2, 0.4) bulk metallic glasses

Magnetic power losses of [(Fe1-xCox)75B20Si5]93Nb4Y3 (x = 0, 0.2, 0.4) metallic glasses have been investigated. Bulk samples were prepared by water-cooled Cu-mold injection casting technique with shapes of cylinders (0.8 mm diameter and 30 mm length) and toroids (10 mm external diameter and 0.5 mm thickness). Ribbons prepared by the melt- spinning technique were also analyzed. Glassy structures were confirmed by the presence of a main halo in XRD and by crystallization signal in DSC. Power losses were studied with a digital wattmeter over a range of frequencies from 1 to 400 Hz at selected peak inductions. Ribbons show smaller losses than bulk samples, presenting 24.5 J/m3 at 50 Hz and 0.65 T peak induction. It was observed that the Co addition reduces significantly the power losses. A separation theory was applied in order to explain the square root behavior of the measured power losses as a function of frequency and the results are in good agreement with the experimental data. The magnetic data were used to identify the presence of crystalline inclusions in the magnetic bulk metallic glasses. The effect of sample shape and composition on magnetic properties will be discussed.

Magnetostriction and dilatation measurements of Fe-Ni-Nb-B metallic glasses

Soft magnetic metallic glasses or their corresponding nanocrystalline counterparts based on Fe and on Ni frequently exhibit different magnetic properties. This work is devoted to rapidly quenched (Fe-Ni)81Nb7B12 ribbon system with the ratio of Ni/Fe being 0, 1/6, 1/3, 1/2, 1, 2 and 3 prepared by planar flow casting. Using temperature dependencies of dilatation, the Curie temperature TC and structural transitions (glass transition, crystallization) were determined. Direct measurement of magnetostriction was employed to determine the values of saturation magnetostriction λS at room temperature. The values for as-quenched samples with low Ni-content (0, 1/6) clearly indicate the proximity of TC to room temperature and thus the values of λS are low. The highest value of λS observed for Ni/Fe = 1/3 is 15.86 ppm. Increasing Ni-content leads to decrease of λS down to 1 ppm for Ni/Fe = 3, in accord with its negative value observed in pure Ni.

Conversion of a glassy antiferromagnetic-insulating phase to an equilibriumferromagnetic-metallic phase by devitrification and recrystallization in Al substitutedPr0.5Ca0.5MnO3

We show that Pr0.5Ca0.5MnO3 with 2.5%Al substitution and La0.5Ca0.5MnO3 (LCMO) exhibit qualitatively similar and visibly anomalousM–H curves at low temperature. Magnetic field causes a broad first order but irreversibleantiferromagnetic (AF)–insulating (I) to ferromagnetic (FM)–metallic (M) transition inboth and gives rise to a soft FM state. However, the low temperature equilibrium state ofPr0.5Ca0.5Mn0.975Al0.025O3 (PCMAO) is FM-M whereas that of LCMO is AF-I. In both systems the respectiveequilibrium phase coexists with the other phase with contrasting order, which is not inequilibrium, and the cooling field can tune the fractions of the coexisting phases. It isshown earlier that the coexisting FM-M phase behaves like ‘magnetic glass’ in LCMO. Herewe show from specially designed measurement protocols that the AF-I phase ofPCMAO has all the characteristics of magnetic glassy states. It devitrifies onheating and also recrystallizes to an equilibrium FM-M phase after annealing. Thisglass-like AF-I phase also shows a similar intriguing feature observed in FM-Mmagnetic glassy state of LCMO, that when the starting coexisting fraction ofglass is larger, successive annealing results in a larger fraction of the equilibriumphase. This similarity between two manganite systems with contrasting magneticorders of respective glassy and equilibrium phases points to a possible universality.

Formation of magnetic Fe-based bulk metallic glass under low vacuum

Bulk metallic glass (BMG) Fe 75Hf 3Mo 3B 15Y 4 can be cast into glassy rod with a diameter of at least 2 mm by copper mold casting technique under a low vacuum of 1.5 Pa. The alloy exhibits a large supercooled liquid region of 57 K and high glass transition temperature of 855 K, demonstrating a good thermal stability. Moreover, the as-cast BMG also shows good soft magnetic properties with a high saturation magnetization of 95 emu/g and low coercivity of around 1.4 Oe at room temperature.

Magnetic cluster glass behavior and grain boundary effect in Nd0.7Ba0.3MnO3 nanoparticles

The magnetic and transport properties of Nd0.7Ba0.3MnO3 nanoparticles were explored by transmission electron microscopy, x-ray powder diffraction, resistivity, magnetoresistance, thermopower (S), and magnetic measurements. The metal-insulator transition behavior of the temperature dependence of resistivity for the sample with the largest particle size changes to insulating nature with the decrease in the particle size due to the enhancement of the grain boundary effect. The magnetoresistance of the nanoparticles is analyzed in the light of a phenomenological model based on the spin polarized tunneling at the grain boundaries. The thermopower of the samples shows a crossover from negative to positive values and at high temperatures S follows adiabatic small polaron hopping theory. The zero field cooled and field cooled (FC) magnetizations display broad ferromagnetic transition. The Curie temperature (TC) and the irreversibility temperature (Tirr) decrease considerably with the decrease in the particle size. During cooling the ac susceptibility of the nanoparticles exhibits two magnetic phase transitions with paramagnetic, ferromagnetic, and glassy phases. The frequency dependent peak in the out of phase part (χ″) of the ac susceptibility is the signature of cluster glass behavior. Large thermomagnetic irreversibility, monotonic increase in the FC magnetization, nonsaturation of the magnetization, and the observation of two distinct magnetic transitions in ac susceptibility give evidence for the cluster glass nature of the nanoparticles.

Effect of Cu Addition on Nanocrystallization Behavior in a Co-Based Soft Magnetic Metallic Glass

Microstructure and magnetic properties of a nanocrystalline soft magnetic material having composition Co64.5 Fe3.5 Si16.5 B13 Ni1.5 Cu1 has been studied. Amorphous ribbon could be produced by melt spinning unit. DSC analysis showed four distinct crystallization events. Heat treated samples were characterized using XRD and TEM techniques. Co2B, and CoB phases were found to crystallize before magnetic phase a−Co. Addition of copper was proved to have adverse effect on soft magnetic properties.

Soft magnetic properties and glass formability of Y–Fe–B–M bulk metals (M = Al, Hf, Nb, Ta, and Ti)

The glass formability, magnetic properties and thermal stability of the Y–Fe–B–M bulk metals (M = Al, Hf, Nb, Ta, and Ti) alloys have been investigated. For (Y 0.06Fe 0.72B 0.22) 98M 2 series alloys, Al or Hf addition deteriorates the glass forming ability (GFA), but Nb or Ta addition broadens supercooled region from 50.2 °C for ternary rod to 61.5 °C for M = Ta and 62 °C for M = Nb, respectively. The bulk glassy rod as large as 3 mm in diameter can be obtained. However, their magnetization and Curie temperature are reduced due to the magnetic dilution by the addition of these nonmagnetic elements. On the other hand, for Y 4Fe 72B 22M 2 series alloys, almost all the substitution elements, except Al, can improve GFA of alloy rod, making the diameter of bulk glassy rod as large as 3 mm for Ti or Hf substitution and 4 mm for Ta or Nb substitution, respectively. It is arisen from the further expansion of the supercooled region to 70.4–84.2 °C. In this study, Y 4Fe 72B 22Ta 2 amorphous rod displays the optimal glass forming ability and also good soft magnetic properties of σ s = 123 emu/g, H c = 0.2 Oe, and T C = 276 °C.

One-pot synthesis of magnetic and mesoporous bioactive glass composites and their sustained drug release property

A novel kind of magnetic and mesoporous bioactive glass (MMBG) composite with Fe 3O 4 nanoparticles confined and dispersed in ordered mesoporous glass matrices has been prepared by a one-pot synthesis route of simultaneous evaporation-induced self-assembly of Ca, P, Si and Fe sources and subsequent reduction in an H 2 atmosphere. The MMBG composites exhibit the type IV isotherm curve with a well-defined step P/ P 0 between 0.4 and 0.8. Ibuprofen storage and release experiments with these composites show adjustable loading amounts from 199 to 420 mg g −1 and a sustained drug release property. A superparamagnetic behavior was identified and the saturation magnetization of the bioactive glass composites was found to increase at increased loading amounts of Fe species. The magnetic and mesoporous bioactive glass composites are believed to be potentially applicable for selectively targeted drug delivery and hyperthermia treatment of bone tumors.

Devitrification and recrystallization of magnetic glassLa0.5Ca0.5MnO3

We report studies on a magnetic glass formed by the arrest of the ferromagnetic-metallic to antiferromagnetic-insulating transition in a manganite around half doping, ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$. The observed glass-to-crystal conversion rate varies drastically and nonmonotonically with temperature; this variation is qualitatively consistent with what we predict by phenomenology. We also show that both homogeneous and heterogeneous nucleation can be obtained in the same sample under different annealing conditions. This gives rise to a gigantic change in resistivity without application of any magnetic field.

Excellent Thermal Stability and Bulk Glass Forming Ability of Fe-B-Nb-Y Soft Magnetic Metallic Glass

Effects of Y addition on the glass forming ability (GFA) of a Fe-B-Nb marginal glass former, and annealing effects on glassy/supercooled liquid phases as well as soft magnetic properties in the multicomponent Fe-B-Nb-Y alloy system were investigated. The origin of highly improved GFA in the multicomponent system is discussed with related to a characteristic exothermic phase transformation, chemical short range ordering, in the supercooled liquid region due to the positive heat of mixing between Nb-Y elements. The separating tendency between Nb and Y elements is considered to suppress precipitation of metastable Fe23B6 and � -Fe crystalline phases, thus to result in highly improving GFA and distinct high thermal stability against heat treatment of the alloy system. In addition, a glassy ring was fabricated by copper mold casting and magnetic properties were investigated before/after heat treatment. [doi:10.2320/matertrans.MBW200732]