Experiments on a heated spin valve reveal clues to the origin of magneto-Seebeck effect
Magnetic materials contain well-ordered collections of electron spins. This makes them ideal for spintronics experiments and studies. But what happens when such a material is heated? Does heat transport affect electron spin transport? Can it be applied as a technology? The emerging new research area of spin-caloritronics strives to answer such questions. Prof. Ashwin Tulapurkar and his team explored the effect of heat on a classic spintronic device – the spin valve, and have found answers to some of its fundamental questions.
The spin valve is essentially a multi-layer structure of different thin films. It has a very thin non-magnetic material sandwiched between two electrically conducting, magnetic layers. Resistance of the magnetic layers depends on the relative directions of their magnetisation, a phenomenon known as giant magnetoresistance (GMR). An interesting observation is that magnetic configuration of the multi-layer spin valve also affects its Seebeck coefficient giving rise to the magneto-Seebeck effect.
Well-known since the 1800s, the Seebeck effect refers to the phenomenon where a temperature difference across junctions of two different materials produces an electric potential difference as well. This team has demonstrated that the primary underlying contribution to the magneto-Seebeck effect in a spin valve comes from its GMR effect itself. They fabricated a spin valve and introduced a thermal gradient at the bottom of the device while measuring the open circuit voltage on top. As expected, this voltage increased along with the temperature gradient. However, it also changed depending on the relative orientation of the two magnetic layers, just like their magnetoresistance.
Understanding the origin of this effect is technologically important due to the wide range of applications of spin valves, such as in magnetic sensors and magnetic random access memory (MRAM).
Work funded/supported by: Dept. of Electrical Engineering, IIT-Bombay; and Dept. of Electronics & Information Technology (DeIT) of Government of India (GoI).
Published paper: S. Jain, D. D. Lam, A. Bose, H. Sharma, V. R. Palkar, C. V. Tomy, Y. Suzuki and A. Tulapurkar, “Magneto-Seebeck effect in spin-valve with in-plane thermal gradient,” AIP Advances, vol. 4, no. 12, 127145 (2014).