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Magnetics, IEEE Transactions on

Issue 6 • Date June 2014

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  • Front cover

    Article#: 0003301
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  • IEEE Transactions on Magnetics publication information

    Article#: 0003401
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  • Table of contents

    Article#: 0100903
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  • International Symposium on Frontiers in Materials Science 2013 Chairmen’s Foreword

    Article#: 0301101
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  • International Symposium on Frontiers in Materials Science 2013 Publication Chair’s Preface

    Article#: 0301201
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  • Role of Interactions in Size-Dependent Curie Temperature of Magnetic Ultrathin Films

    Article#: 1100104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB) |  | HTML iconHTML  

    An arbitrary quantum spin Heisenberg model containing nearest neighbor antiferromagnetic and long-range dipole-dipole interactions, and single ion anisotropy is used to investigate the frustration effect in ultrathin magnetic films. Calculations using functional integral method and Gaussian spin fluctuation approximations showed that thicker films and larger spin S enhance the frustration critical ratio ε = |Js|/Jd where Js and Jd are antiferromagnetic exchange at surfaces and dipolar interaction strengths. The perpendicular positive (negative) anisotropy increases (reduces) this critical value. Results for spin S = 1/2 case are agreed with one of the temperature-dependent Green function method applied for quantum Heisenberg model in random phase approximation. View full abstract»

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  • Spin-Fluctuation-Driven Superconductivity in the Kondo Lattice Model

    Article#: 1300205
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    Superconductivity in solids usually arises due to the generation of an attractive effective interaction between fermions close to the Fermi energy by some bosonic fluctuations. In the conventional theory, these are phonons, but in correlated electron systems like the cuprates or heavy fermions, one believes that the relevant bosonic degrees of freedom are the spin fluctuations. In this context, one usually argues that standard s-wave superconductivity cannot be formed as these spin fluctuations in general lead to a repulsive local interaction. Recently, we observed s-wave superconductivity in the Kondo lattice model using the dynamical mean-field approach. We can indeed show that this superconducting (SC) solution is due to local spin fluctuations arising from the Kondo effect. The reason for these fluctuations mediating an effective attractive interaction lies in the special properties of the heavy electron ground state, i.e., the formation of hybridized bands. Using a simple model, we can show that it is indeed an interband coupling that is largely responsible for the observed SC state. Such an observation is possibly rather interesting also concerning the situation in the pnictide superconductors. View full abstract»

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  • Investigation of the Tunability of the Spin Configuration Inside Exchange Coupled Springs of Hard/Soft Magnets

    Article#: 2004906
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    Magnetic multilayer (ML) structures comprising a perpendicular magnetic anisotropy (PMA) layer coupled to an in-plane magnetic anisotropy (IMA) layer are promising materials for zero/low field operating spin-torque oscillators and bit patterned recording media. The magnetization tilt angle can be easily tuned by varying the IMA layer thickness due to the competition between PMA and IMA layers. To explore the underlying magnetization reversal mechanism and to further understand the control of tilt angle and uniformity of the magnetization, the IMA (NiFe, Co, and CoFeB)/PMA (Co/Pd MLs) exchange spring systems are systematically studied. Experimental data obtained from magnetometry show good agreement with 1-D micromagnetic simulations, allowing us to design tunable exchange coupled spring as a function of IMA thickness. View full abstract»

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  • Effect of Annealing on Magnetic Properties and Giant Magnetoimpedance Effect of Amorphous Microwires

    Article#: 2005004
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    We report on the magnetic properties and giant magnetoimpedance (GMI) effect of amorphous glass-coated Co-rich microwires in as-prepared and annealed states. The magnetic field and frequency dependences of GMI, magnetic hysteresis loops, and domain wall (DW) dynamics of Co69.2Fe4.1B11.8Si13.8C1.1 microwires produced by the Taylor-Ulitovski technique were investigated systematically. We have shown that these properties can be tailored either by controlling magnetoelastic anisotropy of the as-prepared microwires or by controlling their magnetic anisotropy via proper annealing. While the GMI effect has been achieved in an as-prepared microwire, high DW velocity and rectangular hysteresis loops have been observed in its annealed counterpart. View full abstract»

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  • Magnetic Properties of Annealed ${rm Fe}_{65}{rm Co}_{35}$ Powders Prepared By Mechanical Alloying

    Article#: 2005104
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    Fe-Co alloy powders were prepared by mechanical alloying of the elemental Fe and Co powders in air and subsequently annealed at various temperatures. Structural and magnetic characteristics of the annealed powders were studied in detail as a function of annealing temperatures by using an X-ray diffractometer (XRD), a field emission scanning electron microscope, a vibrating sample magnetometer, and a physical property measurement system. The XRD results showed an existence of the nanocrystals with sizes of 15-50 nm. The magnetic studies indicated a strong increase of magnetization and a sharp decrease of coercivity as annealing temperature increased. Both the effect of the oxidation on the magnetic properties as well as magnetization stability of the annealed samples will be discussed. View full abstract»

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  • Electrical Field-Induced Magnetization Switching in CoFe/NiFe/PZT Multiferroics

    Article#: 2005204
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    In this paper, we have investigated the change in magnetization of multiferroic material, based on magnetic nanostructured CoFe/NiFe film grown on the piezoelectric lead zirconate titanate (PZT), under the effect of the strain originated from PZT layer. In this material, a converse magnetoelectric effect and especially, an electric field-induced magnetic anisotropy and magnetization switching process have been observed at the changing stages of applied electric voltage. In addition, a significant relative change in magnetization, above 100%, is obtained, which facilitates practical applications of the materials. This opens possibilities in achieving new types of memory devices, the low energy consumption devices, as well as other functionalities, such as voltage-tunable field sensing. A simple theory based on strain-mediated magnetic-electric coupling is also presented to understand the origin of the change in magnetic properties of the materials. View full abstract»

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  • Enhancing Coercivity of Sintered Nd-Fe–B Magnets by Nanoparticle Addition

    Article#: 2102204
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    In this paper, we investigated the influence of addition of Dy40Nd40Al30 nanoparticles on the structure and magnetic properties of sintered Nd-Fe-B magnets. The nanoparticles with a size smaller than 50 nm were prepared using high-energy ball milling method and then mixed with micrometer Nd2Fe14B powder before magnetic anisotropic pressing, vacuum sintering, and annealing. The structure of the magnets was thoroughly analyzed using X-ray diffraction and electron microscopy techniques. The magnetic properties of the magnets were investigated on a pulsed field magnetometer. The atoms of Dy were detected mainly at the grain boundaries and partly in the near-boundary area of the grains. On adding 2% of the nanoparticles, the coercivity of the magnets is enhanced by quite a large amount, from 12 kOe for the unadded magnets to 21 kOe for the added ones. The large increase of the coercivity is probably due to the diffusion of Dy to the Nd2Fe14B grains to form (Nd,Dy)2Fe14B phases with high magnetocrystalline anisotropy. The nanoparticles might make Dy distribute more homogeneously and diffuse to the Nd2Fe14B grains more efficiently. View full abstract»

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  • Impact of Surface on the $d^{0}$ Ferromagnetism of Lithium-Doped Zinc Oxide Nanowires

    Article#: 2400407
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    We present a first-principles study on the impacts of the surface on the ferromagnetism (FM) induced by non-magnetic defects (lithium substitutional dopants at zinc sites LiZn and zinc vacancies VZn) of zinc oxide (ZnO) nanowires. We show that unlike bulk ZnO structures, both LiZn and VZn are able to induce d0 FM in ZnO nanowires. While the structural confinement at the nanowire surface is found to play a key role in the FM induced by LiZn, the reconstruction of the surface tunes the defect-induced FM. By suppressing the surface reconstruction, we find that a LiZn and a VZn, regardless of their position, induce the same magnetic moments of 0.71 and 2.00 μBB is the magneton Bohr), respectively. The steady correlation between the defect-induced FM, the dangling bonds introduced at these defects, and the local structural reconstruction surrounding these defects is unveiled. Finally, we discuss the saturation of the magnetic moment as the defect density increases. View full abstract»

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  • Optical and Magnetic Properties of Mn-Doped ZnS Nanoparticles Synthesized by a Hydrothermal Method

    Article#: 2400504
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    The Mn-doped ZnS nanoparticles with T2d - F4̅3m cubic structure and an average crystalline size of about 16 nm were synthesized using the hydrothermal method at 220 °C for 15 h from Zn(CH3COO)2 (0.1M), Mn(CH3COO)2 (0.01M), and Na2S2O3 (0.1 M) as the precursors. The appearance of characteristic photoemission bands of Mn2+ (3d5) ions at 390, 430, 467, and 493 nm in the photoluminescence excitation spectra while monitoring the yellow-orange band at 585 nm showed that the Mn2+ (3d10) ions substituted for Zn2+ (3d10) ions in ZnS matrix and caused the ferromagnetism of Mn-doped ZnS nanoparticles. The dependence of photoluminescence, photoluminescence excitation spectra, and magnetization curves on Mn content and the wavelength of excitation radiation were reported. View full abstract»

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  • Nanostructured Iron-Doped Indium Tin Oxide Films: Synthesis and Characterization

    Article#: 2400604
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    Multifunctional, Fe-doped indium tin oxide (ITO) nanostructured films were grown by pulsed laser deposition on sapphire substrates. The films showed low resistivity and n-type conductivity with a carrier density as high as 3 × 1021 cm-3. A magnetic moment at room temperature larger than those of any iron oxides was measured in films with Fe doping as low as 2%. We ascribe it to the formation of bound polarons. A strong green photoemission at room temperature was observed, which we ascribe to quantum confinement effect. The coexistence of ferromagnetism and luminescence in the visible range makes our films of potential for magneto-optoelectronic applications. View full abstract»

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  • Monte Carlo Study of Room-Temperature Ferromagnetism in C-Doped ZnO

    Article#: 2400704
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    The room-temperature ferromagnetism of diluted magnetic semiconductors (DMS) doped with light elements has been extensively studied for potential applications in spintronic devices. The existence and stability of ferromagnetism of DMS with low concentration regime is an interesting topic, followed by researches using both Monte Carlo (MC) simulation and first-principle calculations. Both continuous and discrete spin models were developed to describe the ferromagnetic phase but it is still unclear, which one produces a better outcome. To clarify the issue of a continuous spin model versus a discrete spin model, we have performed a large-scale MC simulation of C-doped ZnO system. We found that the discrete spin model exhibit magnetic phase transition at near room-temperature while the continuous spin model does not show phase transition in the investigated low temperature range. View full abstract»

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  • Optical and Magnetic Properties of ${rm Zn}_{1-x}{rm Mn}_{x}{rm O}$ Grown by Plasma-Assisted Molecular Beam Epitaxy

    Article#: 2400804
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    Zn1-xMnxO films (0 ≤ ×≤ 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x ≤ 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect. View full abstract»

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  • Comparative Study of Room-Temperature Ferromagnetism in Undoped and Mn-Doped CdSe Quantum Dots

    Article#: 2400904
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    We report a comparative study of room-temperature ferromagnetism (RTFM) in undoped and Mn-doped CdSe quantum dots (QDs) synthesized by a pyrolysis method. Both undoped and Mn-doped CdSe QDs exhibited the RTFM with a coercive field of ~160 Oe. The magnetic moment of the QDs showed a strong dependence on the QD size, indicating that the RTFM of the QDs was due to an intrinsic effect. The saturation magnetization value of QDs increased with a decreasing of the QD size. Compared with the undoped QDs, the Mn-doped CdSe QDs exhibited the enhancement of saturation magnetization value with a slight doping concentration. By further increasing the Mn doping concentration to 4 at.%, the increase of the saturation magnetization value of the doped-QDs was not observed, which could be attributed to the enhancement of antiferromagnetic coupling between Mn2+ ions. View full abstract»

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  • Magnetocaloric Effect and Magnetoresistance Due to Itinerant Electron Metamagnetic Transition in ${rm Co}({rm S}_{1-x}{rm Se}_{x})_{2}$

    Article#: 2501806
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    The Co(S1-xSex)2 compounds with the cubic Pyrite structure show itinerant electron metamagnetism for 0.12 ≤ x. We studied the magnetocaloric effect and magnetoresistance (MR) of this system. It was found that a substantial magnetic entropy change was obtained for Co(S0.88Se0.12)2, which has a paramagnetic ground state. We observed giant positive MR associated with the itinerant electron metamagnetic transition for Co(S1-xSex)2. The magnitude of the MR jump is independent of temperature and concentration for 0.13 ≤ x ≤ 0.15. These results are discussed in terms of a simple band structure of CoS2, in which high-spin polarization is realized in a ferromagnetic state. View full abstract»

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  • Effect of Nanocrystallization on Magnetic Properties and GMI Effect of Microwires

    Article#: 2501905
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    We studied giant magnetoimpedance (GMI) effect and magnetic properties of FINEMET-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor-Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires or controlling their structure by heat treatment or changing the fabrication conditions. We observed considerable magnetic softening of studied microwires after annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous microwires exhibited low GMI effect (GMI ratio below 5%). Considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat treated microwires with nanocrystalline structure. Some of as-prepared Fe-rich exhibited nanocrystalline structure and the GMI ratio up to 45%. View full abstract»

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  • Influence of Mn Doping on the Structure, Optical,and Magnetic Properties of ${rm PbTiO}_{3}$ Material

    Article#: 2502004
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    In this paper, the influences of the Mn2+ doping on the structure, optical, and magnetic properties of PbTi1-x MnxO3 (with x = 0.00, 0.03, 0.06, 0.08, 0.10, and 0.12), prepared by the sol-gel method have been investigated by X-ray diffraction (XRD), Raman scattering, optical absorption, and vibrating sample magnetometer measurements. The detailed analysis of XRD patterns showed that the tetragonal lattice distorted ratio (c/a) decreased undesirably with the increasing of Mn content. However, c/a ratio increased again after calcining at higher temperature. The shift to the lower wavenumber and the broadening of some Raman peaks, such as E(2TO) and A1(2TO), indirectly indicated the incorporation of Mn2+ ions into PbTiO3 (PTO) lattice. Absorption spectra exhibited a remarkable decrease of effective optical bandgap (Eg) from 2.99 eV for pure PTO to 1.5 eV for Mn-doped PTO. Therefore, Mn-doped PTO material may be considered as a promising material for photovoltaic and photocatalytic application. In addition, the diamagnetic nature of pure PTO disappeared and the ferromagnetism gradually increased as the Mn content increases. The saturation magnetization Ms varied from 0.014 emu/g for pure PTO to 0.064 emu/g for the PbTi0.88 Mn0.12O3 (Mn12) sample. The nature of this ferromagnetic order in samples could be assigned to the incorporation of ion Mn2+ in PTO lattice. View full abstract»

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  • Crystallization Process and Magnetic Properties of Amorphous ${rm NiFe}_{2}{rm O}_{4}$ Nanoparticles

    Article#: 2502104
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    We investigate the crystallization process of NiFe2O4 nanoparticles prepared by microwave heating technique, which were then characterized using X-ray diffraction, high-resolution transmission electron microscopy, the differential scanning calorimetry, Raman scattering, Fourier transformed infrared spectra (FTIR), and magnetic measurements. The results showed that crystallization of the amorphous NiFe2O4 nanoparticles occurred at around 300 °C. The best crystallization quality would be obtained by annealing the sample at 500 °C. After crystallization, the sample shows ferromagnetic behavior with a saturation magnetization of about 30 emu/g. The FTIR and Raman measurements also provided further information about the crystallization process and the phase transformation of the NiFe2O4 nanoparticles. View full abstract»

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  • Inhomogeneous Ferromagnetism and Spin-Glass-Like Behavior in $({rm Nd}_{1-x}{rm Y}_{x})_{0.7}{rm Sr}_{0.3}{rm MnO}_{3}$ With $x=0.21{-}0.35$

    Article#: 2502204
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    The magnetic properties of polycrystalline ceramic samples (Nd1-xYx)0.7Sr0.3MnO3 with x = 0.21 - 0.35 were studied by means of dc magnetization and ac susceptibility measurements. Experimental results reveal a strong decrease of the ferromagnetic (FM)-paramagnetic phase-transition temperature (TC) from 97 to 65 K as increasing x from 0.21 to 0.35, respectively. There is magnetic inhomogeneity associated with short-range FM order. Particularly, the samples undergo a spin-glass (SG) phase transition at the so-called blocking temperature (TB) below TC, which shifts toward lower temperatures with increasing the applied field, Hex; TB → Tg (the SG phase-transition temperature) as Hex → 0. The existence of the SG behavior in these samples was also confirmed by frequency (f) dependences of the ac susceptibility. For the in-phase/real component, χ'(T), it shows a frequency-dependent peak at the SG freezing temperature (Tf); Tf → Tg as f → 0. Dynamics of this process were analyzed by means of the slowing down scaling law, τ/τ0 ∝ (Tf /Tg - 1)-zv, where τ0 and zv are the characteristic time and critical exponent, respectively. Fitting the experimental Tf (f) data to the scaling law gave the results of zv = 10.1-12.3 and τ0 = 10-21-10-15s. These values are different from those expected for canonical SG systems with zv = 10 and τ0 = 10-13s, revealing the cluster-SG behavior of (Nd1-xYx)0.7Sr0.3MnO3 samples. Notably, the increase in Y content leads to the shift of τ0 and zv values toward those of canonical SG systems, which is ascribed to an expansi- n of SG clusters. View full abstract»

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  • Substitution Mechanism of Mn and Fe Ions in ${rm Bi}_{4}{rm Ti}_{3}{rm O}_{12}$

    Article#: 2502306
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    Single-phased polycrystalline Mn- and Fe-doped Bi4Ti3O12 were fabricated using a solid-state reaction technique, doping with various concentrations of Mn and Fe ions. Substitution mechanism of Mn and Fe ions in Bi4Ti3O12 were investigated with X-ray absorption near-edge structure (XANES) measurements and first-principles calculations. The valence states of the Mn and Fe ions are 4+ and 3+, respectively, inferred from the L2,3-edge XANES profiles. From the K-edge XANES analysis, it is determined that Mn and Fe ions are substituted at one of the Ti sites, i.e., Ti(2a) or Ti(4e) sites. Our first-principles total electronic energy calculations suggest that Mn ions are likely to substitute at Ti(2a) sites rather than at Ti(4e) sites, whereas the opposite is true for Fe substitution. Taken together, these results give a clear description of the locations and charge states of the Mn and Fe dopants in Bi4Ti3O12. View full abstract»

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  • Electrical and Magnetotransport Properties of ${rm La}_{{0.7}}{rm Ca}_{{0.3}}{rm Mn}_{{1-x}}{rm Co}_{{x}}{rm O}_{3}$

    Article#: 2502404
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    This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of La0.7Ca0.3Mn1-xCoxO3(x = 0.09-0.17) prepared by solid-state reaction. Magnetic measurements versus temperature revealed gradual decrease of the magnetization (M) and Curie temperature (TC) with increasing Co concentration (x). The TC values vary from 194 to 159 K as changing x from 0.09 to 0.17, respectively. H/M versus M2 performances around TC prove the x = 0.09 sample undergoing a first-order magnetic phase transition (FOMT) while the samples with x ≥ 0.11 undergo a second-order magnetic phase transition (SOMT). The other with x = 0.10 is considered as a threshold concentration of the FOMT-SOMT transformation. Considering temperature dependences of resistivity, ρ(T), in the presence and absence of the magnetic field, the samples (excepting x = 0.17) exhibit a metal-insulator transition at TP = 60-160 K, which shifts toward lower temperatures with increasing x. the metallic-ferromagnetic region, the ρ(T) data are well fitted to a power function ρ(T) = ρ0 + ρ2 T2 + ρ4.5 T4.5. This indicates electron-electron and electron-magnon scattering processes are dominant at temperatures T <; TP. In addition, the conduction data at temperatures T > θD/2 (θD is the Debye temperature) and TP <; T <; θD/2 obey the small-polaron and variable-range hopping models, respectively. The values of activation energy Ep, and density of states at the Fermi level N(EF) were accordingly determined. Here, N(EF) increases while Ep decreases when an external magnetic field is applied. We also have found that N(EF) - ncreases when materials transfer from the FOMT to the SOMT, and N(EF) value becomes smallest for the sample having the coexistence of the FOMT and SOMT (i.e., x = 0.10). View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology