2,170 research outputs found
Thermodynamics of Two Dimensional Magnetic Nanoparticles
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
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
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 NdNiO
We report detailed magnetization measurements on the perovskite oxide
NdNiO. 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
We report a systematic study on the structural and magnetic properties of
Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between to 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 ( K \leqq K for d nm ) and large coercive fields ( kA/m for K).
The smallest particles ( 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 through the empirical Br\"{u}khatov-Kirensky
relation. This approach provided values very similar to the bulk
material from either static or dynamic magnetic measurements, as well as
realistic values for the response times ( s).
Deviations from the bulk anisotropy values found for the smallest particles
could be qualitatively explained based on Zener\'{}s relation between
and M(T)
Inferring Patient Fear from Word Properties in Pediatric Psychotherapy
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
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
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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