Spin‐Driven Emergent Antiferromagnetism and Metal–Insulator Transition in Nanoscale p‐Si

Physica Rapid Research Ltrs

2018

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The spin‐Seebeck effect mediated thermoelectric energy conversion can provide an efficient alternative to traditional thermoelectrics for waste heat recovery. To achieve this goal, efficient spin to charge conversion using earth‐abundant materials is essential. Proximity induced Rashba effect arises from the charge potential mediated by structural inversion asymmetry, which has been reported in Si thin films and can be manipulated by controlling the thickness of Rashba layer. We demonstrate a giant Rashba spin‐Seebeck effect in NiFe/p‐Si (polycrystalline) bilayer thin films. The bilayer thin film specimens have p‐Si layer thickness of 5, 25, and 100 nm while keeping the NiFe layer thickness at 25 nm. The Rashba spin‐Seebeck coefficient has been estimated to be 0.266 μV K−1 for 100 nm p‐Si, and increases by an order of magnitude to 2.11 μV K−1 for 5 nm p‐Si. The measured spin‐Seebeck coefficient in 5 nm p‐Si specimen is one of the largest coefficients ever reported. The measured voltage of 100.3 μV is one of the largest reported spin‐Seebeck voltages, with smallest area of ≈160 × 10 μm2 used in any spin‐Seebeck measurement. This scientific and technological breakthrough using earth abundant elements brings the spin mediated thermoelectric energy conversion for waste heat recovery closer to reality.

Section: The Summary Of Largest Spin‐seebeck Voltages and Correspondisupporting

confidence: 92%

supporting

confidence: 80%

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confidence: 89%

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Giant Enhancement in Rashba Spin‐Seebeck Effect in NiFe/p‐Si Thin Films

Bhardwaj

Physica Rapid Research Ltrs

2018

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“…The electrical measurement of spin-dependent behavior requires an efficient spin to charge conversion, which is absent in pure p-Si. We hypothesized that Rashba spin orbit coupling due to structure inversion asymmetry (SIA) may allow efficient spin to charge conversion [18] [19], which has been reported for both p-Si and n-Si [20][21][22][23]. To test this hypothesis, we deposited a layer of 1 nm of MgO on the p-Si thin film to have SIA and Rashba spin orbit coupling; the MgO/Si interface is observed to have localized electronic states [24].…”

mentioning

confidence: 96%

Generation and detection of dissipationless spin current in a MgO/Si bilayer

J. Phys.: Condens. Matter

2018

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Spintronics is an analogue to electronics where the spin of the electron rather than its charge is functionally controlled for devices. The generation and detection of spin current without ferromagnetic or exotic/scarce materials are two of the biggest challenges for spintronics devices. In this study, we report a solution to the two problems of spin current generation and detection in Si. Using non-local measurement, we experimentally demonstrate the generation of helical dissipationless spin current using the spin-Hall effect. Contrary to the theoretical prediction, we observe the spin-Hall effect in both n-doped and p-doped Si. The helical spin current is attributed to the site-inversion asymmetry of the diamond cubic lattice of Si and structure inversion asymmetry in a MgO/Si bilayer. The spin to charge conversion in Si is insignificant due to weak spin-orbit coupling. For the efficient detection of spin current, we report spin to charge conversion at the MgO (1 nm)/Si (2 µm) (p-doped and n-doped) thin film interface due to Rashba spin-orbit coupling. We detected the spin current at a distance of >100 µm, which is an order of magnitude larger than the longest spin diffusion length measured using spin injection techniques. The existence of spin current in Si is verified from the coercivity reduction in a Co/Pd multilayer due to spin-orbit torque generated by spin current from Si.

“…In addition, the Rashba SOC mediated spin-Hall magnetoresistance has been reported in Ni 81 Fe 19 /MgO/p-Si thin films 56 and in n-Si 57 . The mechanistic explanation of the observed behavior is given in Figure 4.…”

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confidence: 98%

Spin Seebeck effect and thermal spin galvanic effect in Ni80Fe20/p-Si bilayers

Bhardwaj

Applied Physics Letters

2018

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The development of spintronics and spin-caloritronics devices need efficient generation, detection and manipulation of spin current. The thermal spin current from spin-Seebeck effect has been reported to be more energy efficient than the electrical spin injection methods. But, spin detection has been the one of the bottlenecks since metals with large spin-orbit coupling is an essential requirement. In this work, we report an efficient thermal generation and interfacial detection of spin current. We measured a spin-Seebeck effect in Ni 80 Fe 20 (25 nm)/p-Si (50 nm) (polycrystalline) bilayers without heavy metal spin detector. The p-Si, having the centosymmetric crystal structure, has insignificant intrinsic spin-orbit coupling leading to negligible spin-charge conversion. We report a giant inverse spin-Hall effect, essential for detection of spin-Seebeck effect, in the Ni 80 Fe 20 /p-Si bilayer structure, which originates from Rashba spin orbit coupling due to structure inversion asymmetry at the interface. In addition, the thermal spin pumping in p-Si leads to spin current from p-Si to Ni 80 Fe 20 layer due to thermal spin galvanic effect and spin-Hall effect causing spin-orbit torques. The thermal spin-orbit torques leads to collapse of magnetic hysteresis of 25 nm thick Ni 80 Fe 20 layer. The thermal spin-orbit torques can be used for efficient magnetic switching for memory applications. These scientific breakthroughs may give impetus to the silicon spintronics and spin-caloritronics devices. 3 The performance of thermoelectric semiconductors, especially commercially available, has been stagnant for years. The materials that show increase in thermoelectric performance require complex and scarce (rare earth) elements. An innovative approach to improving thermoelectric energy storage and conversion is the spin dependent thermoelectric energy conversion using spin Seebeck effect (SSE), anomalous Nernst effect (ANE) and spin Nernst effect (SNE), which will bring efficiencies because pure spin current, as opposed to charge current, is believed to be dissipationless 1 . The discovery of Spin Seebeck effect (SSE) by Uchida et. al. has led to significant progress in ongoing research on generation of pure spin current, a precession of spins or flow of electrons with opposite spins in opposite directions, over a large distance in spintronic devices due to applied temperature gradient in ferromagnetic (FM) materials 2-4 . The SSE can be an efficient way to produce low cost and large memory spintronics devices 5 . The SSE is observed in ferromagnetic metals 3,6-11 , semiconductors 12-15 , insulators [16][17][18][19][20][21][22] and even in half metallic Heusler compounds 23 . In the spin caloritronics studies, homogenous temperature gradient as well as length scale dependent temperature gradient is established to study the interplay of spin degrees of freedom and temperature gradient in the magnetic structures 22 . There are two universal SSE device configuration, longitudinal spin Seebeck effect (LSSE) and tr...