First- and second-harmonic detection of spin accumulation in a multiterminal lateral spin valve under high-bias ac current

Abstract

We have investigated the transport properties of electrically and thermally excited spin currents in a lateral spin valve consisting of a spin injector and detector with a middle ferromagnetic wire by detecting the first-and secondharmonic voltages. The first-harmonic spin signal was significantly suppressed by the middle ferromagnetic wire because of the spin absorption effect. On the other hand, in the second-harmonic signal, a small signal related to the middle ferromagnetic wire was observed in addition to a conventional spin signal with a reduced magnitude. This indicates that the additional ferromagnetic wire acts not only as the spin absorber but also as another spin injector under thermal spin injection, because the heat current caused by direct spin injection propagates to the middle ferromagnetic wire and creates another temperature gradient. By using this effect, we show that the magnetization direction of a ferromagnetic nanodot embedded in a nonmagnetic Cu wire becomes measurable.

INFLUENCE OF THE MAGNITUDE AND DIRECTION OF DC-INJECTION CURRENT ON SPIN ACCUMULATION AND THERMOEMF IN NiCo-InSb-NiCo LATERAL SPIN VALVE

“…Nowdays, multilayer spin-valve structures with vertical arrangement of the injection and detection ferromagnetic electrodes (FM) separated by a thin layer of a paramagnetic metal or insulator are applied as an "active" element in the majority of spintronic devices [10]. However, there is a growing interest to investigation of spin-valve structures with lateral geometry of injection and detection FM electrodes connected by a "bridge" of paramagnetic metal [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25], semiconductor [26][27][28][29][30][31][32], graphen [33,34] or conducting polymer material [35]. This location of FM electrodes in a lateral spin-valve structure (LSV) gives it possible to separate injection's circuit of spinpolarized current and detection's circuit by means of a non-local geometry of spin injection and accumulation proposed in [36].…”

“…non-magnetic (NM) material and cleanliness of interface between FM metal and NM material. Thus, to increase the spin accumulation voltage, strong ferromagnetic materials with high spin polarization like NiFe [12-19, 21, 22, 32, 33, 35], FeCo [25], Co [14,15,23,30,34], CoFeAl [11,18], Co 2 FeSi [20,24,31] and nonmagnetic materials with the highest spin diffusion length are applied to form FM and NM electrodes.…”

“…Currently, LSV structures based on polycrystalline films of ferromagnetic and paramagnetic metals Cu [13][14][15][16][17][18][19][20][21][22][23][24][25], Al [14,25], Ag [12,17,25], Au [15,25] got the most widespread due to simplicity of fabrication such structures. However, spin diffusion length of paramagnetic metals commonly less than few hundreds nanometers [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]37]. By this reason, the magnitude of spin accumulation voltage U s measured in non-local geometry for FM-NM metal based LSV structures is of few microvolts magnitude at cryogenic temperature [11][12][13][14][15][16][17][18][19][20][...…”

“…However, spin diffusion length of paramagnetic metals commonly less than few hundreds nanometers [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]37]. By this reason, the magnitude of spin accumulation voltage U s measured in non-local geometry for FM-NM metal based LSV structures is of few microvolts magnitude at cryogenic temperature [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Note, that U s for such LSV can be increased to few hundreds microvolts at cryogenic temperatures by using the tunnel barrier between FM and NM metals [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Effective suppression of thermoelectric voltage in nonlocal spin-valve measurement

“…An observed small finite background voltage indicates that the heat current due to the Peltier effect generated in the J 3 junction partially diffuses into the substrate during the propagation in the Cu strip between Py2 and Py3. 17) Then, we measure the nonlocal spin-valve signal for the half configuration, where the current and voltage probes are located at the same side, as schematically shown in Fig. 4(a).…”