다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R04/pdf

Recent developments in magnetocaloric materials

We present a review of experimental and theoretical studies of the anomalous Hall effect (AHE), focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical work, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents which originate from spin-orbit coupling. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors, have more clearly established systematic trends. These two developments in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of Berry-phase curvatures and it is therefore an intrinsic quantum mechanical property of a perfect cyrstal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. We review the full modern semiclassical treatment of the AHE together with the more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Finally we discuss outstanding issues and avenues for future investigation.

/pdf/anomalous-hall-effect-tyeyld308t.pdf

Anomalous hall effect

The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs)1,2 is the key to developing magnetoresistive random-access-memory (MRAM), magnetic sensors and novel programmable logic devices3,4,5. Conventional MTJs with an amorphous aluminium oxide tunnel barrier, which have been extensively studied for device applications, exhibit a magnetoresistance ratio up to 70% at room temperature6. This low magnetoresistance seriously limits the feasibility of spintronics devices. Here, we report a giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs. The origin of this enormous TMR effect is coherent spin-polarized tunnelling, where the symmetry of electron wave functions plays an important role. Moreover, we observed that their tunnel magnetoresistance oscillates as a function of tunnel barrier thickness, indicating that coherency of wave functions is conserved across the tunnel barrier. The coherent TMR effect is a key to making spintronic devices with novel quantum-mechanical functions, and to developing gigabit-scale MRAM.

Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers

The effect of the application of an external magnetic field in the paramagnetic phase of the giant magnetocaloric compound ${\mathrm{Tb}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ has been studied by means of macroscopic (magnetostriction and magnetoresistance) and microscopic neutron powder diffraction experiments. As a main result, we have discovered the existence of a ferromagnetic monoclinic phase in these intriguing 5:4 compounds. Long-range ferromagnetism sets in within the monoclinic structure on cooling down before the structural transformation into the orthorhombic phase takes place. Our results may shed some light into understanding the complex coupling between crystallographic and magnetic degrees of freedom and the mechanisms that trigger the field-induced processes in the ${\mathrm{Tb}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$ compounds.

Magnetic-martensitic transition of Tb 5 Si 2 Ge 2 studied with neutron powder diffraction

The magnetocaloric effect has been investigated in a series of the R5(SixGe1−x)4 pseudobinary alloys with R=Tb and x=00, 05, and 10 In Tb5Si4 and Tb5Ge4, a maximum magnetic entropy change of 98 and 37 J/kg K, respectively, has been found at their ordering temperatures for a magnetic field change of 50 kOe In the case of Tb5Ge4, we have observed the existence of a previously unreported magnetic transition below the Neel temperature Tb5(Si05Ge05)4 has been successfully synthesized, and a large entropy change of 218 J/kg K (ΔH=50 kOe) is achieved at a first-order para- to ferromagnetic transition, TC≅105 K This study demonstrates that Tb5(SixGe1−x)4 alloys are good candidates for magnetic refrigeration and that very exciting phenomenology in these systems awaits further investigation

Magnetocaloric effect in Tb5(SixGe1−x)4

We present very low temperature Scanning Tunneling Microscopy and Spectroscopy (STM/S) measurements in W-based amorphous superconducting nanodeposits grown using a metal-organic precursor and focused-ion-beam. The superconducting gap closely follows s-wave BCS theory, and STS images under magnetic fields show a hexagonal vortex lattice whose orientation is related to features observed in the topography through STM. Our results demonstrate that the superconducting properties at the surface of these deposits are very homogeneous, down to atomic scale. This, combined with the huge nanofabrication possibilities of the focused-ion-beam technique, paves the way to use focused-ion-beam to make superconducting circuitry of many different geometries.

Nanoscale superconducting properties of amorphous W-based deposits grown with focused-ion-beam

We have studied the magnetic and power absorption properties of three samples of CoFe2O4 nanoparticles with sizes from 5 to 12 nm prepared by thermal decomposition of Fe (acac)3 and Co(acac)2 at high temperatures. The blocking temperatures TB estimated from magnetization M(T) curves spanned the range 180 ≤ T B ≤ 320 K, reflecting the large magnetocrystalline anisotropy of these nanoparticles. Accordingly, high coercive fields HC ≈ 1.4 - 1.7 T were observed at low temperatures. Specific Power Absorption (SPA) experiments carried out in ac magnetic fields indicated that, besides particle volume, the effective magnetic anisotropy is a key parameter determining the absorption efficiency. SPA values as high as 98 W/g were obtained for nanoparticles with average size of ≈ 12 nm.

http://www.unizar.es/gfgoya/index_archivos/PDF/CoFe2O4_Hyperthermia_ICM.pdf

M. R. Ibarra

Papers

Magnetic-martensitic transition of Tb 5 Si 2 Ge 2 studied with neutron powder diffraction

Magnetocaloric effect in Tb5(SixGe1−x)4

Nanoscale superconducting properties of amorphous W-based deposits grown with focused-ion-beam

Magnetic properties and energy absorption of CoFe2O4 nanoparticles for magnetic hyperthermia

Structural, magnetic and transport properties of Sr2Fe1−xCrxMoO6−y