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.

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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 linear thermal expansion, AC susceptibility and magnetostriction have been measured on a single crystal of HoAl2. The authors' results clearly show two phase transitions associated, respectively, with establishment of magnetic order and with spontaneous spin reorientation. The critical exponent gamma SR of the susceptibility for T>or approximately=TSR has been determined. From magnetostriction measurements along the major symmetry directions of the crystal, they have obtained the possible deformation modes compatible with the point symmetry of the cubic crystal structure. A complete study of the magnetoelastic behaviour has allowed them to determine the reduced magnetoelastic coupling coefficients M2gamma /Cgamma , M2epsilon /Cepsilon , Mlalpha /Calpha (l=4,6) and Dalpha /Calpha . The model used is based on a single-ion origin for the crystal electric field interaction of the rare-earth ion, and they have taken into account the spontaneous reorientation of the magnetic moment in the molecular field, which represents the exchange interaction.

http://iopscience.iop.org/article/10.1088/0022-3719/21/14/013/pdf

Magnetoelastic behaviour and the spin-reorientation transition in HoAl2

Autocatalytic growth of Co on pure Co surfaces using Co2(CO)8 precursor

The evolution of the morphology, magnetic and transport properties of Fe(t nm)/MgO(3.0 nm) multilayers with respect to the nominal metallic layer thickness was investigated. A comparison with existing experimental data on discontinuous metal–insulator multilayers, ultrathin epitaxial Fe films on MgO substrates and granular cermet films is made. It is confirmed that the deposition conditions and the material composition play a crucial role in the percolation process. Nominal thicknesses of Fe layers at which an infinite metallic cluster is formed and the conditions for continuous Fe coverage were determined. Different methods of percolation threshold detection were analysed. We show that investigation of the temperature dependence of resistance in nanostructures could lead to an overestimation of the percolation threshold value, while magnetic measurements alone could lead to its underestimation.

http://iopscience.iop.org/article/10.1088/0953-8984/22/5/056003/pdf

Determination of the percolation threshold in Fe/MgO magnetic granular multilayers

Magnetic anisotropy and spin-reorientation in HoAl2

Neutron diffraction results on the intermetallic compound YCu show that the low-temperature phase is of orthorhombic FeB type, space group Pnma with a=7.0936 AA, b=4.5254 AA, c=5.4030 AA. The copper coordination is sevenfold and the overall structure may be regarded as a vestige of the cubic high-temperature CsCl modification.

https://iopscience.iop.org/article/10.1088/0953-8984/5/4/001/pdf

M. R. Ibarra

Papers

Magnetoelastic behaviour and the spin-reorientation transition in HoAl2

Autocatalytic growth of Co on pure Co surfaces using Co2(CO)8 precursor

Determination of the percolation threshold in Fe/MgO magnetic granular multilayers

Magnetic anisotropy and spin-reorientation in HoAl2

The low-temperature orthorhombic structure of YCu