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 95 Mo and 97 Mo NMR spin-echo study of (Sr,Ba,La)2Fe1+yMo1iyO6 double perovskites is reported Powder samples of Ba1:44Sr0:36La0:2FeMoO6 and (Ba0:8Sr0:2)2i2xLax#xFe1+yMo1iyO6, where # denotes vacancies, for: x = 0; y = 0; x = 0:1; x = 0:2 and x = 0:3; y = 0 and y = 0:2 were measured at 42 K and no applied magnetic fleld NMR signals are observed at 55{100 MHz for the main line and 30{55 MHz for low-frequency satellite The main line and the satellite are attributed to the ideal and defect positions of Mo atoms La and vacancy doping introduce more defects, however, increasing the Fe/Mo ratio decreases the amount of defect Mo sites La doping causes a satellite pattern at the high frequency side of the spectrum, which is related to difierent numbers of the La next neighbours The efiect is attributed to an increase in the electron density and the corresponding magnetic moment at the adjacent Mo sites and reveals a local character of the electron doping

/pdf/nmr-study-of-sr-ba-la-2-fe-1-y-mo-1-y-o-6-double-perovskites-45y95824gg.pdf

NMR Study of (Sr;Ba;La) 2 Fe 1+y Mo 1¡y O 6 Double Perovskites

Electronic instability in YMn2 driven by Ni substitution: An x-ray absorption investigation

Magnetic anisotropy has been measured for the ferromagnetic La07Sr03CoO3 perovskite from an analysis of the high-field part of the magnetization vs field curves, ie, the magnetic saturation regime These measurements give a magnetic anistropy one order of magnitude higher than that of reference manganites Surprisingly, the values of the magnetic anisotropy calculated in this way do not coincide with those estimated from measurements of coercive fields which are one order of magnitude smaller It is proposed that the reason of this anomalous behaviour is a transition of the trivalent Co ions under the external magnetic field from a low-spin to an intermediate-spin state Such a transition converts the Co3+ ions into Jahn-Teller ions having an only partially quenched orbital angular momentum, which enhances the intra-atomic spin-orbit coupling and magnetic anisotropy

/pdf/field-induced-magnetic-anisotropy-in-la0-7sr0-3coo3-52d97lue9n.pdf

Field-induced magnetic anisotropy in La0.7Sr0.3CoO3

TbCu suffers a structural transformation at TN = 117 K, with the establishment of a collinear antiferromagnetic order. On the other hand, YCu is a Pauli paramagnet, which also transforms structurally at Ts = 150 K. In order to test the influence of the magnetoelastic energy as the driving mechanism of the transition in TbCu, we have performed neutron diffraction experiments on the compound Tb0.6Y0.4Cu. From the thermal evolution of the structural and magnetic peaks, we have observed that both, structural (Ts) and magnetic transitions (TN), occur at different temperatures. This separation in the transition temperatures constitutes a strong indication that magnetoelastic energy is not responsible for the transition in TbCu, in spite of the large magnetostriction observed at low temperatures at the metamagnetic field induced transition.

M. R. Ibarra

Papers

NMR Study of (Sr;Ba;La) 2 Fe 1+y Mo 1¡y O 6 Double Perovskites

Electronic instability in YMn2 driven by Ni substitution: An x-ray absorption investigation

Field-induced magnetic anisotropy in La0.7Sr0.3CoO3

Study of the influence of the magnetoelastic energy in driving the magnetic and structural transition in TbCu

Publisher's Note: Pressure Enhancement of the Giant Magnetocaloric Effect in T b 5 S i 2 G e 2 [Phys. Rev. Lett. 93 , 137201 (2004)]