2,170 research outputs found

    Thermodynamics of Two Dimensional Magnetic Nanoparticles

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    A two dimensional magnetic particle in the presence of an external magnetic field is studied. Equilibrium thermodynamical properties are derived by evaluating analytically the partition function. When the external field is applied perpendicular to the anisotropy axis the system exhibits a second order phase transition with order parameter being the magnetization parallel to the field. In this case the system is isomorph to a mechanical system consisting in a particle moving without friction in a circle rotating about its vertical diameter. Contrary to a paramagnetic particle, equilibrium magnetization shows a maximum at finite temperature. We also show that uniaxial anisotropy in a system of noninteracting particles can be missinterpreted as a ferromagnetic or antiferromagnetic coupling among the magnetic particles depending on the angle between anisotropy axis and magnetic field.Comment: 4 pages 6 figures 19 reference

    Giant magnetoimpedance in crystalline Mumetal

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    We studied giant magnetoimpedance (GMI) effect in commercial crystalline Mumetal, with the emphasis to sample thickness dependence and annealing effects. By using appropriate heat treatment one can achieve GMI ratios as high as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best GMI characteristics obtained for amorphous and nanocrystalline soft magnetic materials.Comment: 8 pages, 3 figure

    Structural and magnetic study of a dilute magnetic semiconductor: Fe doped CeO2 nanoparticles

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    This paper reports the effect of Fe doping on the structure and room temperature ferromagnetism of CeO2 nanoparticles. X-ray diffraction and selective area electron diffraction measurement reflects that Ce1-xFexO2 (x = 0.0 - 0.07) nanoparticles exhibit single phase nature with cubic structure and none of the sample showed the presence of any secondary phase. The mean particle size calculated by using a transmission electron microscopy measurement was found to increase with increase in Fe content. DC magnetization measurements performed at room temperature indicates that all the samples exhibit ferromagnetism. The saturation magnetic moment has been found to increase with an increase in the Fe content.Comment: 16 Pages, 5 figure, 1 Table, Accepted in JN

    Spin canted magnetism, decoupling of charge and spin ordering in NdNiO3_3

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    We report detailed magnetization measurements on the perovskite oxide NdNiO3_3. This system has a first order metal-insulator (M-I) transition at about 200 K which is associated with charge ordering. There is also a concurrent paramagnetic to antiferromagnetic spin ordering transition in the system. We show that the antiferromagnetic state of the nickel sublattice is spin canted. We also show that the concurrency of the charge ordering and spin ordering transitions is seen only while warming up the system from low temperature. The transitions are not concurrent while cooling the system through the M-I transition temperature. This is explained based on the fact that the charge ordering transition is first order while the spin ordering transition is continuous. In the magnetically ordered state the system exhibits ZFC-FC irreversibilities, as well as history-dependent magnetization and aging. Our analysis rules out the possibility of spin-glass or superparamagnetism and suggests that the irreversibilities originate from magnetocrystalline anisotropy and domain wall pinning.Comment: 8 pages, 7 figure

    Validity of the N\'{e}el-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles

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    We report a systematic study on the structural and magnetic properties of Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between 55 to 2525 nm, prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (4242 K \leqq TBT_B ≦345\leqq 345 K for 5≦5 \leqq d ≦13\leqq 13 nm ) and large coercive fields (HC≊1600H_C \approxeq 1600 kA/m for T=5T = 5 K). The smallest particles (=5=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the N\'{e}el-Arrhenius relaxation framework without the need of ad-hoc corrections, by including the thermal dependence of the magnetocrystalline anisotropy constant K1(T)K_1(T) through the empirical Br\"{u}khatov-Kirensky relation. This approach provided K1(0)K_1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (τ0≃10−10\tau_0 \simeq 10^{-10} s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener\'{}s relation between K1(T)K_1(T) and M(T)

    Inferring Patient Fear from Word Properties in Pediatric Psychotherapy

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    Pediatric psychotherapy, specifically cognitive behavioral therapy (CBT), is a promising treatment for Obsessive-Compulsive Disorder (OCD). Clinical fear ratings obtained during pediatric psychotherapy provide valuable information about patient progress and have been associated with clinical outcomes. Evidence-based treatments rely on patient fear ratings, but no methods have been developed that can automatically extract fear ratings during psychotherapy. Advancements in computational methods have shown promise in detecting stress from written text that could be used to inform mental health diagnoses. We use a tool made to find the essential meaning of written text and machine learning models to predict patient fear ratings during 434 recorded pediatric OCD therapy sessions. Results indicate there are correlations between clinical fear ratings and the semantic features of words spoken during pediatric OCD therapy. Certain patients are prone to providing consistently low fear ratings, thus impacting the efficacy of machine learning algorithms applied to this dataset. When patients could be in the training and testing data of the machine learning models produced in this study, the area under the receiver operating characteristics (ROC) curve was higher than when patients were separated into either the training or testing data. These findings suggest that it may be possible to extract personality traits from the words spoken during therapy, indicating a correlation between the words spoken during therapy and patient fear

    Magnetic hysteresis in granular CuCo alloys

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    Room-temperature hysteresis loops of granular Cu100-xCox alloys (5 less than or equal to x less than or equal to 15) obtained by planar flow casting in air and submitted to proper annealing treatments have been measured up to a field of 10 kOe by means of a vibrating sample magnetometer. In major loops (\H-vert\ = 10 kOe), the reduced remanence-to-saturation ratio m(r) = M-r/M-s and the coercivity H-c measured on all studied materials appear to be related by an almost linear law of the type m(r) approximate to 1/3 (mu H-c/kT), mu being the average magnetic moment on Co particles. A similar relation is also observed on minor symmetrical loops (100 Oe less than or equal to\H-vert\ less than or equal to 9 kOe). The observed results are accounted for by a model which considers the hysteresis as originating by magnetic interactions among nearly superparamagnetic Co particles. (C) 1999 American Institute of Physics. [S0021-8979(99)51408-4]

    Magnetic properties and giant magnetoresistance in melt-spun CoCu alloys

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    Magnetic, structural, and transport properties of as quenched and annealed Co10Cu90 samples have been investigated using x¿ray diffraction and a SQUID magnetometer. The largest value of MR change was observed for the as¿quenched sample annealed at 450°C for 30 min. The magnetic and transport properties closely correlate with the microstructure, mainly with Co magnetic particle size and its distribution. For thermal annealing the as quenched samples below 600°C, the Co particle diameters increase from 4.0 to 6.0 nm with a magnetoresistance (MR) drop from 33.0% to 5.0% at 10 K. Comparison with the theory indicates that the interfacial electron spin¿dependent scattering mechanism correlates with GMR for Co particle diameters up to about 6.0 nm
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