輝也 新庄

Bio: 輝也 新庄 is an academic researcher. The author has contributed to research in topics: Colossal magnetoresistance & Tunnel magnetoresistance. The author has an hindex of 1, co-authored 1 publications receiving 11 citations.

Spin dependent transport in magnetic nanostructures

Abstract: Experiments of Giant Magnetoresistance. Theory of Giant Magnetoresistance. Experiment of Tunnel Magnetoresistance. Theory of Tunnel Magnetoresistance. Applications of Magnetic Nanostructures.

Currents, torques, and polarization factors in magnetic tunnel junctions

Abstract: Bardeen's transfer-Hamiltonian method is applied to magnetic tunnel junctions having a general degree of atomic disorder. The results reveal a close relationship between magnetoconduction and voltage-driven pseudotorque, and also provide a means of predicting the thickness dependence of tunnel-polarization factors. Among the results: (i) The torque generally varies with moment direction as $\mathrm{sin}\phantom{\rule{0.2em}{0ex}}\ensuremath{\theta}$ at constant applied voltage. (ii) Whenever polarization factors are well defined, the voltage-driven torque on each moment is uniquely proportional to the polarization factor of the other magnet. (iii) At finite applied voltage, this relation implies significant voltage-asymmetry in the torque. For one sign of voltage the torque remains substantial even if the magnetoconductance is greatly diminished. (iv) A broadly defined junction model, called ideal middle, allows for atomic disorder within the magnets and $\mathrm{F}∕\mathrm{I}$ interface regions. In this model, the spin-$(\ensuremath{\sigma})$ dependence of a basis-state weighting factor proportional to the sum over general state index $p$ of ${(\ensuremath{\int}\ensuremath{\int}dydz{\ensuremath{\Psi}}_{p,\ensuremath{\sigma}})}^{2}$ evaluated within the (e.g., vacuum) barrier generalizes the local state density in previous theories of the tunnel-polarization factor. (v) For small applied voltage, tunnel-polarization factors remain legitimate up to first order in the inverse thickness of the ideal middle. An algebraic formula describes the first-order corrections to polarization factors in terms of newly defined lateral autocorrellation scales.

Origin, development, and future of spintronics (Nobel Lecture).

Abstract: Electrons have a charge and a spin, but until recently, charges and spins have been considered separately. In conventional electronics, the charges are manipulated by electric fields but the spins are ignored. Other classical technologies, such as magnetic recording, use the spin but only through its macroscopic manifestation, the magnetization of a ferromagnet. This picture started to change in 1988 when the discovery of giant magnetoresistance (GMR) of the magnetic multilayers opened the way to efficient control of the motion of the electrons by acting on their spin through the orientation of a magnetization. This rapidly triggered the development of a new field of research and technology, which is today called spintronics and exploits the influence of the spin on the mobility of the electrons in ferromagnetic materials. Actually, the influence of the spin on the mobility of the electrons in ferromagnetic metals, first suggested by Mott, had been experimentally demonstrated and theoretically described in my PhD thesis more than ten years before the discovery in 1988. The discovery of GMR was the first step on the road towards exploiting this influence to control an electrical current. Its application to the read head of hard disks greatly contributed to the fast rise in the density of stored information and led to the extension of hard-disk technology to consumer electronics. Then, the development of spintronics revealed many other phenomena related to the control and manipulation of spin currents. Today this field of research is extending considerably, with very promising new directions such as spin transfer, spintronics with semiconductors, molecular spintronics, or singleelectron spintronics. From the

Four-state ferroelectric spin-valve

Abstract: Spin-valves had empowered the giant magnetoresistance (GMR) devices to have memory. The insertion of thin antiferromagnetic (AFM) films allowed two stable magnetic field-induced switchable resistance states persisting in remanence. In this letter, we show that, without the deliberate introduction of such an AFM layer, this functionality is transferred to multiferroic tunnel junctions (MFTJ) allowing us to create a four-state resistive memory device. We observed that the ferroelectric/ferromagnetic interface plays a crucial role in the stabilization of the exchange bias, which ultimately leads to four robust electro tunnel electro resistance (TER) and tunnel magneto resistance (TMR) states in the junction.

Design Rules: Industrial Research and Epistemic Merit

Abstract: A common complaint against the increasing privatization of research is that research that is conducted with the immediate purpose of producing applicable knowledge will not yield knowledge as valuable as that generated in more curiosity-driven, academic settings. In this paper, I make this concern precise and reconstruct the rationale behind it. Subsequently, I examine the case of industry research on the giant magnetoresistance effect in the 1990s as a characteristic example of research undertaken under considerable pressure to produce applicable results. The example permits one to arrive at a more optimistic assessment of the epistemic merits of private, application-driven research. I attempt to specify the conditions that, in this case, advanced the production of interesting and reliable knowledge.

Aharonov-Bohm effect and giant magnetoresistance in graphene nanoribbon rings

Abstract: We report a numerical study on the Aharonov-Bohm (AB) effect and giant magnetoresistance in rectangular rings made of graphene nanoribbons (GNRs). We show that in the low-energy regime where only the first subband of contact GNRs contributes to the transport, the transmission probability can be strongly modulated, i.e., almost fully suppressed, when tuning a perpendicular magnetic field. On this basis, strong AB oscillations with giant negative magnetoresistance can be achieved at room temperature. The magnetoresistance reaches thousands of percent in perfect GNR rings and a few hundred percent with edge-disordered GNRs. The design rules to observe such strong effects are also discussed. Our study hence provides guidelines for further investigations of the AB interference and to obtain high magnetoresistance in graphene devices.