Conversion of charge current into pure spin current and vice versa in non-magnetic semiconductors or metals, which are called the direct and inverse spin Hall effects (SHEs), provide a new functionality of materials for future spin-electronic architectures. Thus, the realization of a large SHE in a device with a simple and practical geometry is a crucial issue for its applications. Here, we present a multi-terminal device with a Au Hall cross and an FePt perpendicular spin injector to detect giant direct and inverse SHEs at room temperature. Perpendicularly magnetized FePt injects or detects perpendicularly polarized spin current without magnetic field, enabling the unambiguous identification of SHEs. The unprecedentedly large spin Hall resistance of up to 2.9 mOmega is attributed to the large spin Hall angle in Au through the skew scattering mechanism and the highly efficient spin injection due to the well-matched spin resistances of the chosen materials.

The Technical Committee of the IEEE Magnetics Society has selected 7 research topics to develop their roadmaps, where major developments should be listed alongside expected timelines; (i) hard disk drives, (ii) magnetic random access memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and actuators, (vi) magnetic materials and (vii) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used for example as a cell for a magnetic random access memory and spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarised electrons efficiently into a non-magnet. We have accordingly identified 2 key properties to be achieved by developing new magnetic materials for future spintronic devices: (1) Half-metallicity at room temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For the first property, 5 major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: Heusler alloys, ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level EF only for its minority spins, achieving 100% spin polarisation at EF. We have also evaluated L10-alloys and D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarisation. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations and interdisciplinary applications within 35 years time scale.Comment: Open Access, 11 pages, 11 figures, advance online publication IEEE Transactions on Magnetic

Spatial distribution of temperature modulation due to anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt / yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE strongly depends on the direction of magnetization, leading to the remarkable different temperature profiles in the FePt thin film between the in-plane and perpendicularly magnetized configurations. (99 words) * Spin-current (J s )-mediated interconversion between electric charge current (J c ) and heat current (J q ), research field of which is frequently called "spin caloritronics" [1], has largely fascinated us from the viewpoint of not only fundamental physics but also potential applications. Spin Seebeck effect (SSE) [2-4] and spin Peltier effect (SPE) [5,6] are representative phenomena of spin caloritronics. SSE enables us to convert a temperature gradient (∇T) to pure J s owing to the collective magnetization dynamics activated by ∇T [7,8]. On the other hand, SPE is the reverse process of SSE, in which the flow of J s produces J q due to the transfer of spin angular momentum and energy from conduction electron spins to local spins, and vice versa, and the resultant non-equilibrium states of the magnon and electron systems [5]. Eventually, the SPE induces ∇T along J s . In both cases of SSE and SPE, junctions consisting of ferromagnetic and paramagnetic materials are often studied [2,3,5,6,9], e.g. a ferrimagnetic insulator yttrium iron garnet (YIG) and a paramagnetic metal Pt. For SSE, the J s due to the non-equilibrium spin state at the ferromagnet / paramagnet interface is observed as electric voltage in the paramagnet via the spin-orbit interaction, i.e. a spin Hall effect (SHE) [10]. The SPE has recently been observed in junctions with YIG and Pt by using microfabricated thermopiles [5] and active infrared emission microscopy called lock-in thermography (LIT) [6,11,12]. J s was generated via the SHE of Pt by the J c flow, and the interaction of J s and spontaneous magnetization (M) of YIG modulated the temperature of the junction.In addition to the SSE and SPE, anomalous Nernst effect (ANE) and anomalous Ettingshausen effect (AEE) are famous thermoelectric phenomena in ferromagnets that have been known for a long time [13], in

The anomalous Nernst effect (ANE) has been investigated in alternately-stacked multilayer films comprising paramagnetic and ferromagnetic metals. We found that the ANE is enhanced with increasing the number of the paramagnet/ferromagnet interfaces with keeping the total thickness of the films constant, and that the enhancement appears even in the absence of magnetic proximity effects; similar behavior was observed not only in Pt/Fe multilayers but also in Au/Fe and Cu/Fe multilayers free from proximity ferromagnetism. This universal enhancement of the ANE in the metallic multilayers suggests the presence of unconventional interface-induced thermoelectric conversion in the Fe films attached to the paramagnets.PACS numbers: 72.15. Jf, 73.50.Lw, The anomalous Nernst effect (ANE) is one of the transverse thermoelectric effects in ferromagnetic materials [1][2][3][4][5][6][7]. The electric field induced by the ANE E ANE is generated via spin-orbit interaction in the direction of the cross product of the spontaneous magnetization M and applied temperature gradient ∇T :where S ANE is the anomalous Nernst coefficient. Although the ANE is a well-known phenomenon having a long research history, it is drawing renewed attention in the field of spintronics [6,8]. From the viewpoint of fundamental physics, key targets in the ANE research include microscopic understanding of the mechanism of this phenomenon [2,4,7] and separation of the ANE from the spin Seebeck effects (SSEs) [9][10][11][12][13][14][15][16][17][18][19][20]. From the viewpoint of applications, development of novel thermoelectric generation technology based on the ANE is already in progress [5]. Recently, the ANE has been investigated also in paramagnetic metals connected to ferromagnetic materials for revealing the effect of magnetic proximity on thermal spin-transport phenomena [21,22]. In a paramagnet/ferromagnet junction system, when the paramagnet is near the Stoner ferromagnetic instability (e.g., Pt and Pd) [23,24], ferromagnetism may be induced in the paramagnet in the vicinity of the paramagnet/ferromagnet interface due to static magnetic proximity effects. If the proximity ferromagnetism is combined with spin-orbit interaction, the ANE may appear even in the paramagnetic materials. In 2012, Huang et al. [21] pointed out that the proximity-induced ANE (PANE) might contaminate the longitudinal SSE (LSSE) [12][13][14][15][16][17][18][19][20] in Pt/Y 3 Fe 5 O 12 (YIG) junction systems, which are commonly used for investigating spin-current phenomena. Followed by this problem presentation, we experimentally demonstrated that transverse thermoelectric voltage in Pt/YIG systems is due purely to the LSSE and established a method for the clear separation of the PANE from the LSSE [14,18,20]. In 2014, Guo et al. [25] theoretically investigated the PANE in ferromagnetic Pt and Pd within Berry-phase formalism based on relativistic band-structure calculations; the magnitude of the PANE coefficient for Pt on YIG was predicted to be small: S ANE ∼ 0.06 µV/K. The PAN...

We investigated anomalous Ettingshausen effect (AEE) and anomalous Nernst effect (ANE) for the same device consisting of an FePt thin film. The temperature modulation due to the AEE was visualized using the active infrared emission microscopy, called lock-in thermography. On the other hand, the ANE voltage was detected under the temperature gradient induced by the heater built into the device. We experimentally evaluated the magnitudes of AEE and ANE, taking into account the heat loss to the substrate, and discussed the relationship between AEE and ANE.

We show, both experimentally and theoretically, a novel route to obtain giant room temperature spin-Hall effect due to surface-assisted skew scattering. In the experiment, we report the spin-Hall effect in Pt-doped Au films with different thicknesses t(N). The giant spin-Hall angle γ(S)=0.12±0.04 is obtained for t(N)=10 nm at room temperature, while it is much smaller for the t(N)=20 nm sample. Combined ab initio and quantum Monte Carlo calculations for the skew scattering due to a Pt impurity show γ(S)≅0.1 on the Au (111) surface, while it is small in bulk Au. The quantum Monte Carlo results show that the spin-orbit interaction of the Pt impurity on the Au (111) surface is enhanced, because the Pt 5d levels are lifted to the Fermi level due to the valence fluctuation. In addition, there are two spin-orbit interaction channels on the Au (111) surface, while only one in bulk Au.

Current-induced magnetization reversal of perpendicularly magnetized layers was studied in current-perpendicular-to-plane giant magnetoresistance pillars with L10-FePt (001) layers. The FePt layers exhibited strong perpendicular magnetic anisotropy of the order of 107erg∕cm3. A series of magnetoresistance curves after applying pulse currents with different current densities showed that current-induced magnetization reversal from an antiparallel to a parallel alignment occurred at the current density of the order of 108A∕cm2 with the assistance of magnetic field.

No abstract