Temperature dependence of magnetic properties of heat treated cobalt ferrite

This study demonstrates the effectiveness of heat treatment in optimizing the magneticproperties of cobalt ferrite, compared to other methods such as cation substitution. It also shows how the magnetic properties of the heat treated cobalt ferrite vary under differenttemperature conditions. Saturation magnetization increased more due to heat treatment than due to Zn-substitution; a cation substitution that is known to result in high saturationmagnetization in ferrites. A remarkable observation is that the increase in the saturationmagnetization due to heat treatment was not at the expense of Curie temperature as was often reported for cation substituted materials. The observed variations in the magnetic propertieswere explained on the basis of cation redistribution arising as a result of the heat treatment

Fine structure observation in magnetostriction near the transition temperature in Gd5Si1.95Ge2.05

Gd5(Si\rm xGe1 -\rm x)4 has a complex magnetic-structural phase diagram which can be divided into three distinct regions. It exhibits an unusual first-order coupled magnetic-structural phase transition in the region \rm x \u3c 0.51. A series of magnetostrictive strain measurements were carried out as a function of magnetic field strength at different temperatures and as a function of temperature at near-zero magnetic field strengths. In this paper, we report for the first time the observation of fine structure in the variation of strain with magnetic field near the first-order phase transition temperature. This fine structure was observed only for the single-crystalline and polycrystalline samples of Gd5 Si 1.95 Ge2.05 but not for Gd5 Si2 Ge2 and Gd5 Si2.09 Ge1.91 samples. There was a sudden increase of about 200-300 ppm in the magnetostrictive strain just prior the field-induced first-order phase transition. In this paper, this anomaly is termed as fine structure. It was observed in measurements of both magnetostrictive strain versus magnetic field and magnetostrictive strain versus temperature. In the case of the polycrystalline Gd5Si 1.95Ge2.05 sample, this anomaly was not as sharp, and the sudden magnetostrictive strain change was about 40 ppm just before the field-induced first-order phase transition

New Physics Effects in B→K(∗)ννB \to K^(*) \nu \nu Decays

We present a model-independent analysis of rare B decays, $B \to K^{(*)} \nu \nu$. The effect of possible new physics is written in terms of dimension-6 four-fermi interactions. The lepton number violating scalar- and tensor-type interactions are included, and they induce $B \to K^{(*)} \nu \nu ({\bar \nu} {\bar \nu})$ decays. We show systematically how the branching ratios and missing mass-squared spectrum depend on the coefficients of the four-fermi interactions.Comment: 20 pages with 7 figure

Direct CP and T Violation in Baryonic B Decays

We review the direct CP and T violation in the three-body baryonic B decays in the standard model. In particular, we emphasize that the direct CP violating asymmetry in $B^\pm\to p\bar p K^{*\pm}$ is around 22% and the direct $T$ violating asymmetry in \bar B^0 \ra \Lambda \bar p \pi^+ can be as large as 12%, which are accessible to the current B factories at KEK and SLAC as well as SuperB and LHCb.Comment: 6 pages, Talk given at 4th International Conference on Flavor Physics (ICFP 2007), Beijing, China, 24-28 Sep 200

Growth and characterisation of Gd5(SixGe1−x)4 thin film

We report for the first time successful growth of magnetic thin films containing the Gd5(Six Ge1−x)4 phase, which is expected to show giant magnetocaloric properties. The film wasdeposited by Pulsed Laser Deposition (PLD) on a (001) silicon wafer at 200  °C from a polycrystalline Gd5Si2.09 Ge 1.91 target prepared by arc melting. PLD was achieved using a femto second laser with a repetition rate of 1 kHz, and a pulse energy of up to 3.5 mJ. The average film thickness was measured to be 400 nm using a Scanning Electron Microscopy and the composition of the film was analyzed using Energy Dispersive Spectroscopy and found to be close to the target composition. X-Ray Diffraction analysis confirmed the presence of Gd5Si2Ge 2 monoclinic structure. Magnetic moment vs. magnetic field measurement confirmed that the film was ferromagnetic at a temperature of 200 K. The transition temperature of the film was determined from a plot of magnetic moment vs. temperature. The transition temperature was between 280 and 300 K which is close to the transition temperature of the bulk material

Possible Supersymmetric Effects on Angular Distributions in B→K∗(→Kπ)ℓ+ℓ−B \to K^* (\to K \pi) \ell^+ \ell^- Decays

We investigate the angular distributions of the rare B decay, $B \to K^* (\to K \pi) \ell^+ \ell^-$, in general supersymmetric extensions of the standard model. We consider the new physics contributions from the operators $O_{7,8,9,10}$ in small invariant mass region of lepton pair. We show that the azimuthal angle distribution of the decay can tell us the new physics effects clearly from the behavior of the distribution, even if new physics does not change the decay rate substantially from the standard model prediction

Transcranial magnetic stimulation: Improved coil design for deep brain investigation

This paper reports on a design for a coil for transcranial magnetic stimulation. The design shows potential for improving the penetration depth of the magnetic field, allowing stimulation of subcortical structures within the brain. The magnetic and induced electric fields in the human head have been calculated with finite element electromagnetic modeling software and compared with empirical measurements. Results show that the coil design used gives improved penetration depth, but also indicates the likelihood of stimulation of additional tissue resulting from the spatial distribution of the magnetic field

Thermally activated decomposition of (Ga,Mn)As thin layer at medium temperature post growth annealing

The redistribution of Mn atoms in Ga1-xMnxAs layer during medium-temperature annealing, 250-450 oC, by Mn K-edge X-ray absorption fine structure (XAFS) recorded at ALBA facility, was studied. For this purpose Ga1-xMnxAs thin layer with x=0.01 was grown on AlAs buffer layer deposited on GaAs(100) substrate by molecular beam epitaxy (MBE) followed by annealing. The examined layer was detached from the substrate using a “lift-off” procedure in order to eliminate elastic scattering in XAFS spectra. Fourier transform analysis of experimentally obtained EXAFS spectra allowed to propose a model which describes a redistribution/diffusion of Mn atoms in the host matrix. Theoretical XANES spectra, simulated using multiple scattering formalism (FEFF code) with the support of density functional theory (WIEN2k code), qualitatively describe the features observed in the experimental fine structure

Temperature dependence of magnetic anisotropy of Ga-substituted cobalt ferrite

The temperature dependence of magnetization, magnetic anisotropy, and coercive field of gallium-substituted cobaltferrite was investigated for a series of compositions of CoGaxFe2−xO4 (0⩽x⩽0.8). Hysteresis loops were measured for each sample over the range of −5T⩽μ0H⩽5T for selected temperatures between 10 and 400K. The magnetization at 5T and low temperatures was found to increase for the lower Ga contents (x=0.2 and 0.4) compared to pure CoFe2O4, indicating that at least initially, Ga3+substitutes predominantly into the tetrahedral sites of the spinel structure. The high field regions of these loops were modeled using the law of approach to saturation, which represents the rotational process, together with an additional linear forced magnetization term. The first order cubic magnetocrystalline anisotropy coefficient K1 was calculated from curve fitting to these data. It was found that K1 decreased with increasing Ga content at all temperatures. Both anisotropy and coercivity increased substantially as temperature decreased. Below 150K, for certain compositions (x=0, 0.2, 0.4), the maximum applied field of μ0H=5T was less than the anisotropy field and, therefore, insufficient to saturate the magnetization. In these cases, the use of the law of approach method can lead to calculated values of K1 which are lower than the correct value