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

Thermal expansion and magnetic properties of the YFe11−xCoxTi compounds have been investigated by various experimental methods. A large magnetovolume effect has been clearly observed below TC for the Fe-rich compounds. When the transition metal concentration changes from Fe to Co rich, the invar-like effect becomes less pronounced and almost disappears close to the pure-Co compound. The dependence of the spontaneous volume magnetostriction on temperature and Co concentration has been estimated from the thermal expansion measurements. It has been found that, for the YFe11−xCoxTi compounds, the largest spontaneous volume magnetostriction (about 2.1%) occurs at x=3, close to the concentration in which a maximum in saturation magnetization was found. The anomalous thermal expansion can be attributed to the volume dependence of the magnetic energy, which is very sensitive to the distance between first-neighbors transition-metal atoms for Fe-rich compounds.

/pdf/magnetovolume-effects-of-y-fe-co-ti-intermetallics-46hm2yuqgh.pdf

Magnetovolume effects of Y-Fe-Co-Ti intermetallics

Magnetostriction of (rare earth) Ni2 intermetallic compounds

Extraordinary effects of the hydrostatic pressure on the crystallographic and magnetic properties of the ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$ alloy have been examined by means of macroscopic (magnetization and linear thermal expansion) and microscopic (neutron powder diffraction) techniques. The high-temperature $O(\mathrm{I})\ensuremath{\leftrightarrow}M$ crystallographic transformation (observed at ${T}_{t}\ensuremath{\cong}215\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at atmospheric pressure) shifts to low temperatures at the unexpectedly high rate of $d{T}_{t}∕dP\ensuremath{\cong}\ensuremath{-}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$. In addition, the application of pressure induces an $O(\mathrm{I})$ reentrance in the low-temperature ferromagnetic state of ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$. The latter transformation $({T}_{t2})$ is a reversible first-order-type structural phase transition shifting towards high temperature with pressure at a much lower rate of $d{T}_{t2}∕dP\ensuremath{\cong}+6\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$. This low-temperature $O(\mathrm{I})$ crystal structure has a Curie temperature higher than that of the monoclinic polymorph, pointing out the importance of the interlayer covalentlike bonding to enhance the ferromagnetic interactions in these alloys. Above $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, both structural transformations collapse, yielding a stable $O(\mathrm{I})$ phase throughout the whole temperature range. In light of these experimental findings, a complete $P\text{\ensuremath{-}}T$ magnetic-crystallographic phase diagram of ${\mathrm{Er}}_{5}{\mathrm{Si}}_{4}$ has been constructed.

Effects of pressure on the magnetic and crystallographic structure of Er 5 Si 4

The magnetic anisotropy of the DyFe11Ti intermetallic has been studied by measuring the angular dependence of the components of the magnetization parallel and perpendicular to the applied magnetic field. The measurements were performed on two plate-shaped samples with the surfaces parallel to the (110) and (001) planes, respectively. From the measurements in the (110) plane the thermal dependence of the spin reorientation angle has been obtained. The magnetic field dependence of M/sub /// and Mperpendicular to showed a first-order magnetization process (FOMP). A single-ion model for the crystal-electric-field interaction and a mean-field model for the exchange interaction have been used to explain theoretically the experimental results. An in-depth study of the character of the spin reorientation transition from easy cone to easy plane has been undertaken. From our study we show that for temperatures near this spin reorientation temperature, two magnetic phases (planar and conical phases) coexist in the sample, giving rise to an average angle that evolves continuously with temperature. A similar behaviour has been also observed for magnetic fields near the critical field of the FOMP, producing a continuous change of the magnetization instead of a jump at the critical field.

https://robots.iopscience.iop.org/article/10.1088/0953-8984/6/48/016/pdf

Magnetic anisotropy and magnetic phase transitions in a DyFe11Ti single crystal

Magnetostriction on single crystals of Y2Fe17 and Er2Fe17 has been measured in pulsed high magnetic fields up to 15 T in the temperature range between 5 and 300 K. We have observed large jumps in the magnetostriction on Er2Fe17, related to first order magnetization processes induced when the magnetic field is applied along the hard magnetic c-axis.

M. R. Ibarra

Papers

Magnetovolume effects of Y-Fe-Co-Ti intermetallics

Magnetostriction of (rare earth) Ni2 intermetallic compounds

Effects of pressure on the magnetic and crystallographic structure of Er 5 Si 4

Magnetic anisotropy and magnetic phase transitions in a DyFe11Ti single crystal

Magnetostriction in pulsed high magnetic fields of RE2Fe17 single crystals