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In order to obtain "table-like" magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (–ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum –ΔSM value of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of –ΔSM for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle. [ABSTRACT FROM AUTHOR]

Transcranial Magnetic Stimulation has the potential to treat various neurological disorders noninvasively and safely. The "Halo coil" configuration can stimulate deeper regions of the brain with lower surface to deep-brain field ratio compared to other coil configurations. The existing "Halo coil" configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current "Halo coil" design along with a graphical user interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable "Halo coil" configuration can stimulate different regions of the brain by adjusting the position and orientation of the larger coil on the head. We have calculated magnetic and electric fields inside a MRI-derived heterogeneous head model for various positions and orientations of the coil. We have also investigated the mechanical and thermal stability of the adjustable "Halo coil" configuration for various positions and orientations of the coil to ensure safe operation of the system. [ABSTRACT FROM AUTHOR]

This work presents investigations and detailed analysis of ringing in a non-resonant pulsed nuclear magnetic resonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirable that those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of the magnetic core used in the antenna (acting as an inductive load). We will demonstrate that an LRC subcircuit is also set-up due to the inductive load and needs to be considered due to its parasitic effects. It is observed that the parasitics associated with the inductive load become important at certain frequencies. The output response can be related to the response of an under-damped circuit and to the magnetic core material. This research work demonstrates and discusses ways of controlling ringing by considering interrelationships between different contributing factors. [ABSTRACT FROM AUTHOR]

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3 thin films. CrxBi2-xTe3 thin films with x=0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2-xTe3. When x=0.14 and 0.29, ferromagnetism appears in CrxBi2-xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration. The Arrott-Noakes plot demonstrates that the critical mechanism of the ferromagnetism can be described better with 3D-Heisenberg model than with mean field model. Our work may benefit for the practical applications of magnetic topological insulators in spintronics and magnetoelectric devices. [ABSTRACT FROM AUTHOR]

To understand the effect of Co doping on the magnetic entropy changes in Gd2AI phase, a series of Gd2AlCox, alloys with 0 ≤ x ≤ 0.6 were synthesized by arc-melting and the crystal structure was analyzed by XRD. The magnetic properties were investigated, and the entropy changes were calculated for a magnetic field change of 50 kOe. All the as-cast alloys doped with Co exhibited greater magnetic entropy changes than the original binary Gd2AI phase. The main reasons attributed to this are the increase of ferromagnetic interaction indicated by the disappearance of cusp and sharp drop in magnetization and the reduction of the critical field required to trigger the field-induced transition below 50 K in Gd2Al phase after Co alloying. [ABSTRACT FROM AUTHOR]

First order phase transitions may occur in several magnetic systems, with two structural phases having different magnetic properties each and a structural transition between them. Here, a novel physics based phenomenological model of such systems is proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by extended Jiles-Atherton theory) and paramagnetism (described by the Curie-Weiss law) in respective phases. An identification procedure to extract material parameters from experimental data is proposed. The proposed phenomenological approach was successfully applied to magnetocaloric Gd5(SixGe1-x)4 system and also has the potential to describe the behavior of Griffiths phase magnetic systems. [ABSTRACT FROM AUTHOR]

Gd5(SixGe1-x)4 has mixed phases in the composition range 0.32

Gd5(SixGe1-x)4 has mixed phases in the composition range 0.325Si1.3Ge2.7 and Gd5Si1.4Ge2.6. We have investigated the first order and second order phase transition temperatures of these samples using magnetic moment vs. temperature and magnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the "hidden" second order phase transition temperature of the orthorhombic II phase. [ABSTRACT FROM AUTHOR]

Materials exhibiting a large magnetocaloric effect (MCE) at or near room temperature are critical for solid-state refrigeration applications. The MCE is described by a change in entropy (ΔSM) and/or temperature (ΔTad) of a material in response to a change in applied magnetic field. Ball milled materials generally exhibit smaller ΔSM values compared to bulk; however, milling broadens the effect, potentially increasing the relative cooling power (RCP). The as-cast Gd5Si4 is an attractive option due to its magnetic transition at 340 K and associated MCE. Investigation of effect of particles size and transition temperature in the binary material, Gd5Si4, can lead to development of functionally graded bulk material with higher MCE and RCP than the traditional bulk materials. A two-step ball-milling process, in which coarse powder of Gd5Si4 was first milled with poly(ethylene glycol) followed by milling in heptane was used to produce fine particles of Gd5Si4 that showed a broad distribution in particle size. Magnetic measurement on the milled sample obtained after washing with water show a decrease in Curie temperature and significant broadening of the magnetic transition. Compared to bulk Gd5Si4, the maximum MCE of the milled samples is also reduced and shifted down by close to 30 K, but the MCE remains substantial over a broader temperature range. The RCP of both milled samples increased 75% from the bulk material. [ABSTRACT FROM AUTHOR]

The triboelectric energy generators prepared using the combination of self-polarized, high β-phase nanocomposite films of Gd5Si4-PVDF and polyamide-6 (PA-6) films have generated significantly higher voltage of ∼425 V, short-circuit current density of ∼30 mA/m2 and a charge density of ∼116.7 μC/m2 as compared to corresponding values of ∼300 V, 30 mA/m2 and 94.7 μC/m2, respectively for the pristine PVDF-(PA-6) combination. The magnetic measurements of the Gd5Si4-PVDF films display a ferromagnetic behavior as compared to diamagnetic nature of pristine PVDF. The presence of magnetic nanoparticles in the polymeric matrix allows for some control over the microstructural properties during the preparation process. The results open new routes for multiferroic composite films to be suitable for multi-functional magnetic and triboelectric energy harvesting applications. [ABSTRACT FROM AUTHOR]

Successful growth and characterization of thin films of giant magnetocaloric Gd5(SixGe1-x)4 were reported in the literature with limited success. The inherent difficulty in producing this complex material makes it difficult to characterize all the phases present in the thin films of this material. Therefore, thin film of binary compound of Gd5Si4 was deposited by pulsed laser deposition. It was then covered with platinum on the top of the film to protect against any oxidation when the film was exposed to ambient conditions. The average film thickness was measured to be approximately 350 nm using a scanning electron microscopy, and the composition of the film was analyzed using energy dispersive spectroscopy. X-ray diffraction analysis indicates the presence of Gd5Si4 orthorhombic structure along with Gd5Si3 secondary phase. The transition temperature of the film was determined from magnetic moment vs. temperature measurement. The transition temperature was between 320 and 345K which is close to the transition temperature of the bulk material. Magnetic moment vs. magnetic field measurement confirmed that the film was ferromagnetic below 342 K. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation (TMS) offers the possibility of non-invasive treatment of brain disorders in humans. Studies on animals can allow rapid progress of the research including exploring a variety of different treatment conditions. Numerical calculations using animal models are needed to help design suitable TMS coils for use in animal experiments, in particular, to estimate the electric field induced in animal brains. In this paper, we have implemented a high-resolution anatomical MRI-derived mouse model consisting of 50 tissue types to accurately calculate induced electric field in the mouse brain. Magnetic field measurements have been performed on the surface of the coil and compared with the calculations in order to validate the calculated magnetic and induced electric fields in the brain. Results show how the induced electric field is distributed in a mouse brain and allow investigation of how this could be improved for TMS studies using mice. The findings have important implications in further preclinical development of TMS for treatment of human diseases. [ABSTRACT FROM AUTHOR]

Structure and magnetic properties of the GdAl2-GdCo2 system including magnetocaloric effect have been investigated for various compositions. The as-cast GdCoxAl2-x alloys prepared by arc-melting crystallize in the dual-phase structure of cubic MgCu2-type and hexagonal MgZn2-type phases. All the as-cast dual-phase alloys exhibit only one magnetic phase transition near 77K even though two ferrimagnetic phases coexist. The magnetic transition was broadened by the continuous transitions of the component phases, which resulted in enhancement of relative cooling power at the expense of the magnetic entropy changes. [ABSTRACT FROM AUTHOR]

Samples of La0.4Bi0.6Mn1-xTixO3 have been prepared and their microstructure, composition, and magnetic properties have been investigated for x=0.05, 0.1, and 0.5. The deviation in the inverse susceptibility behavior from Curie-Weiss law and increase in susceptibility exponent indicates the evolution of the Griffith's phase in La0.4Bi0.6Mn1-xTixO3 around TC. The presence of Griffith's Phase is inferred due to magnetic frustration with increasing Ti concentration. The deviation between field cooled and zero field cooled magnetization curves is observed in these samples and is attributed to the appearance of the spin glass or cluster glass state that arises due to the magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Irreversible change in resistivity occurs in Gd5(SixGe1-x)4 (with 0.41

Gd5(SixGe1-x)4 exhibits a field induced first order phase transition from a monoclinic paramagnetic to an orthorhombic ferromagnetic at temperatures above its Curie temperature for 0.41≤x≤0.51. The field required to induce the transition increases with temperature. This field induced first order phase transition was observed even above the projected second order phase transition temperature of the orthorhombic phase. This may be due to the fact that the applied magnetic field is so high that it causes the broadening to a wider range of higher temperatures of the second order phase transition of the orthorhombic phase, and at such high magnetic fields the magnetic moment is still quite large, therefore, causing the transition. This hypothesis seems to be confirmed by the various magnetic moment versus magnetic field, magnetic moment versus temperature, and strain versus magnetic field measurements carried out on single crystal Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples at magnetic fields of 0–9 T and at temperatures of 265–305 K. [ABSTRACT FROM AUTHOR]

Gd5(SixGe1-x)4 exhibits a field induced first order phase transition from a monoclinic paramagnetic to an orthorhombic ferromagnetic at temperatures above its Curie temperature for 0.41≤x≤0.51. The field required to induce the transition increases with temperature. This field induced first order phase transition was observed even above the projected second order phase transition temperature of the orthorhombic phase. This may be due to the fact that the applied magnetic field is so high that it causes the broadening to a wider range of higher temperatures of the second order phase transition of the orthorhombic phase, and at such high magnetic fields the magnetic moment is still quite large, therefore, causing the transition. This hypothesis seems to be confirmed by the various magnetic moment versus magnetic field, magnetic moment versus temperature, and strain versus magnetic field measurements carried out on single crystal Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples at magnetic fields of 0–9 T and at temperatures of 265–305 K. [ABSTRACT FROM AUTHOR]

Gd5(SixGe1-x)4 for 0.41≤x≤0.5 is orthorhombic and ferromagnetic at lower temperature, monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. Magnetic moment versus magnetic field (MH) isotherms were measured just above the first order transition temperature for Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples and the field-induced coupled phase transition from paramagnetic/monoclinic to ferromagnetic/orthorhombic phase was observed. Using the method developed by Arrott [Phys. Rev. 108, 1394 (1957)], the ferromagnetic portions of the MH isotherms were used to project the second order magnetic phase transition temperature of the orthorhombic phase, a region where the transition does not occur due to the first order transition at a lower temperature. These data points fall on the extrapolated line of the second order phase transition, drawn from the Si-rich region of the phase diagram. [ABSTRACT FROM AUTHOR]