Magnetism and spin transport in rare-earth-rich epitaxial terbium and europium iron garnet films (original) (raw)
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Advanced electronic materials, 2016
include recently discovered phenomena such as the quantum anomalous Hall effect [2] in magnetic topological insulators (TIs), [3] spin transfer torque [4,5] effects in nonmagnetic metal/ferromagnetic metal/ oxide heterostructures, and spin orbit torque (SOT) effects in heterostructures that include ferromagnetic metals/heavy metals, [6,7] magnetically-doped TIs, [8] and FMI/heavy metals where the FMI is a garnet [9] or Ba hexaferrite. [10] To realize novel circuit devices based on these effects a variety of magnetic materials and heterostructures has still to be developed in which the magnetic properties and interfacial spin transport can be controlled. FMIs with PMA are of particular interest in spintronics. In FMI/heavy metal or FMI/TI heterostructures, current is limited to the metal or to the surface layer of the TI which reduces the conductivity (and potentially the power consumption) compared to all-metallic structures, and avoids the possibility of direct spin transfer torque from current flow in the FMI layer. This facilitates the study of proximity effects, SOT and other exotic phenomena occurring at the interfaces, enabling for example an identification of the various contributions to spin orbit torques. Moreover, the presence of PMA in the FMI leads to stray-field-induced interface effects even at remanence. Domain walls in PMA films also have qualitatively different structures and dynamics compared to those of FMIs with in-plane magnetic anisotropy, which is relevant to racetrack memory or logic devices. Thus there is considerable interest in developing PMA FMI materials and heterostructures. One of the most prominent classes of FMI is that of ferrimagnetic iron garnets, of which the best studied is Y 3 Fe 5 O 12 (YIG). The ultralow damping [11] and magneto-optical properties [12,13] of YIG are well known. The former makes YIG a suitable candidate for spin wave logic [14] and signal transmitters [15] due to the extremely large magnon propagation length of several tens of millimeters. YIG/heavy metal (e.g., Pt, W, Ta) and YIG/topological insulator heterostructures have demonstrated proximity effects, spin pumping, spin Seebeck, and other spintronic phenomena. [15-19] However, YIG films generally have an in-plane easy axis dominated by shape anisotropy due to their weak With recent developments in the field of spintronics, ferromagnetic insulator (FMI) thin films have emerged as an important component of spintronic devices. Ferrimagnetic yttrium iron garnet in particular is an excellent insulator with low Gilbert damping and a Curie temperature well above room temperature, and has been incorporated into heterostructures that exhibit a plethora of spintronic phenomena including spin pumping, spin Seebeck, and proximity effects. However, it has been a challenge to develop high quality sub-10 nm thickness FMI garnet films with perpendicular magnetic anisotropy (PMA) and PMA garnet/heavy metal heterostructures to facilitate advances in spin-current and anomalous Hall phenomena. Here, robust PMA in ultrathin thulium iron garnet (TmIG) films of high structural quality down to a thickness of 5.6 nm are demonstrated, which retain a saturation magnetization close to bulk. It is shown that TmIG/Pt bilayers exhibit a large spin Hall magnetoresistance (SMR) and SMR-driven anomalous Hall effect, which indicates efficient spin transmission across the TmIG/Pt interface. These measurements are used to quantify the interfacial spin mixing conductance in TmIG/Pt and the temperature-dependent PMA of the TmIG thin film.
Applied Physics Letters, 2014
We study the temperature dependence of the spin Hall magnetoresistance (SMR) in yttrium iron garnet/platinum hybrid structures via magnetization orientation dependent magnetoresistance measurements. Our experiments show a decrease of the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR to the spin transport properties of the normal metal, we interpret our data in terms of a decrease of the spin Hall angle in platinum from 0.11 at room temperature to 0.075 at 10 K, while the spin diffusion length and the spin mixing conductance of the ferrimagnetic insulator/normal metal interface remain almost constant.
Applied Physics Letters, 2012
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Tm3 Fe5 O12 /Pt Heterostructures with Perpendicular Magnetic Anisotropy for Spintronic Applications
Advanced Electronic Materials, 2016
include recently discovered phenomena such as the quantum anomalous Hall effect [2] in magnetic topological insulators (TIs), [3] spin transfer torque [4,5] effects in nonmagnetic metal/ferromagnetic metal/ oxide heterostructures, and spin orbit torque (SOT) effects in heterostructures that include ferromagnetic metals/heavy metals, [6,7] magnetically-doped TIs, [8] and FMI/heavy metals where the FMI is a garnet [9] or Ba hexaferrite. [10] To realize novel circuit devices based on these effects a variety of magnetic materials and heterostructures has still to be developed in which the magnetic properties and interfacial spin transport can be controlled. FMIs with PMA are of particular interest in spintronics. In FMI/heavy metal or FMI/TI heterostructures, current is limited to the metal or to the surface layer of the TI which reduces the conductivity (and potentially the power consumption) compared to all-metallic structures, and avoids the possibility of direct spin transfer torque from current flow in the FMI layer. This facilitates the study of proximity effects, SOT and other exotic phenomena occurring at the interfaces, enabling for example an identification of the various contributions to spin orbit torques. Moreover, the presence of PMA in the FMI leads to stray-field-induced interface effects even at remanence. Domain walls in PMA films also have qualitatively different structures and dynamics compared to those of FMIs with in-plane magnetic anisotropy, which is relevant to racetrack memory or logic devices. Thus there is considerable interest in developing PMA FMI materials and heterostructures. One of the most prominent classes of FMI is that of ferrimagnetic iron garnets, of which the best studied is Y 3 Fe 5 O 12 (YIG). The ultralow damping [11] and magneto-optical properties [12,13] of YIG are well known. The former makes YIG a suitable candidate for spin wave logic [14] and signal transmitters [15] due to the extremely large magnon propagation length of several tens of millimeters. YIG/heavy metal (e.g., Pt, W, Ta) and YIG/topological insulator heterostructures have demonstrated proximity effects, spin pumping, spin Seebeck, and other spintronic phenomena. [15-19] However, YIG films generally have an in-plane easy axis dominated by shape anisotropy due to their weak With recent developments in the field of spintronics, ferromagnetic insulator (FMI) thin films have emerged as an important component of spintronic devices. Ferrimagnetic yttrium iron garnet in particular is an excellent insulator with low Gilbert damping and a Curie temperature well above room temperature, and has been incorporated into heterostructures that exhibit a plethora of spintronic phenomena including spin pumping, spin Seebeck, and proximity effects. However, it has been a challenge to develop high quality sub-10 nm thickness FMI garnet films with perpendicular magnetic anisotropy (PMA) and PMA garnet/heavy metal heterostructures to facilitate advances in spin-current and anomalous Hall phenomena. Here, robust PMA in ultrathin thulium iron garnet (TmIG) films of high structural quality down to a thickness of 5.6 nm are demonstrated, which retain a saturation magnetization close to bulk. It is shown that TmIG/Pt bilayers exhibit a large spin Hall magnetoresistance (SMR) and SMR-driven anomalous Hall effect, which indicates efficient spin transmission across the TmIG/Pt interface. These measurements are used to quantify the interfacial spin mixing conductance in TmIG/Pt and the temperature-dependent PMA of the TmIG thin film.
Comparative measurements of inverse spin Hall effects and magnetoresistance in YIG/Pt and YIG/Ta
Physical Review B, 2013
We report on a comparative study of spin Hall related effects and magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements allow to estimate the characteristic transport parameters of both Pt and Ta layers juxtaposed to YIG: the spin mixing conductance G ↑↓ at the YIG|normal metal interface, the spin Hall angle ΘSH, and the spin diffusion length λ sd in the normal metal. The inverse spin Hall voltages generated in Pt and Ta by the pure spin current pumped from YIG excited at resonance confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we extract the spin diffusion length in Ta, found to be λ Ta sd = 1.8 ± 0.7 nm. Both the YIG|Pt and YIG|Ta systems display a similar variation of resistance upon magnetic field orientation, which can be explained in the recently developed framework of spin Hall magnetoresistance.
Physical Review B, 2013
The occurrence of spin-Hall magnetoresistance (SMR) in platinum (Pt) on top of yttrium iron garnet (YIG) has been investigated, for both in-plane and out-of-plane applied magnetic fields and for different Pt thicknesses [3, 4, 8, and 35 nm]. Our experiments show that the SMR signal directly depends on the in-plane and out-of-plane magnetization directions of the YIG. This confirms the theoretical description, where the SMR occurs due to the interplay of the spin-orbit interaction in the Pt and the spin-mixing conductance at the YIG/Pt interface. Additionally, the sensitivity of the SMR and spin pumping signals on the YIG/Pt interface conditions is shown by comparing two different deposition techniques (e-beam evaporation and dc sputtering).
Exchange magnetic field torques in YIG/Pt bilayers observed by the spin-Hall magnetoresistance
Applied Physics Letters, 2013
The effective field torque of an yttrium-iron-garnet (YIG) film on the spin accumulation in an attached platinum (Pt) film is measured by the spin-Hall magnetoresistance (SMR). As a result, the magnetization direction of a ferromagnetic insulating layer can be measured electrically. Experimental transverse and longitudinal resistances are well described by the theoretical model of SMR in terms of the direct and inverse spin-Hall effect, for different Pt thicknesses [3, 4, 8, and 35 nm]. Adopting a spin-Hall angle of Pt h SH ¼ 0:08, we obtain the spin diffusion length of Pt (k ¼ 1:1 6 0:3 nm) as well as the real (G r ¼ ð7 6 3Þ Â 10 14 X À1 m À2 ) and imaginary part (G i ¼ ð5 6 3Þ Â 10 13 X À1 m À2 ) of the spin-mixing conductance and their ratio (G r =G i ¼ 16 6 4).