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Tomoyasu Taniyama
Tomoyasu Taniyama
Laboratory for Materials and Structures, Tokyo Institute of Technology, Japan
Manipulation of antiferromagnetic-ferromagnetic phase transition of ordered FeRh and beyond


Spintronics that harnesses the spin angular momentum of an electron has attracted great attention for crafting new low-power device applications [1]. While the use of ferromagnetic (FM) materials is essentially required for spin-related functionalities in spintronic devices, antiferromagnetic (AFM) materials are used as alternative material candidates recently [2]. With a view to incorporating further additional functionalities into these spintronic devices, manipulation of the magnetic phases such as ferromagnetic and antiferromagnetic phases will be an exciting issue although it is still at a very challenging stage. In order to tackle this issue, here we focus on the intriguing magnetic properties of B2 ordered FeRh alloys such as the AFM-FM transition at around 380 K, accompanied by an isotropic volume expansion ~1% and a giant variation of resistivity [3]. In this presentation, I will review recent progress in our research of manipulating the AFM-FM phase transition by external means. 

After a brief introduction of the fundamental magnetic properties of FeRh, I will discuss interfacial strain effects on the AFM-FM transition in FeRh/BaTiO3 heterostructures [4]. Since there is a strong coupling between the lattice and spin in FeRh, the magnetoelastic effect that is induced by strain at the FeRh/BaTiO3 interface arising from the structural phase transition and piezoelastic effect of BaTiO3 [5] enables to manipulate the magnetic phases of FeRh. We find that compressive interfacial strain generated by the structural phase transition and an electric field efficiently induces the FM-AFM transition in FeRh/BaTiO3. The mechanism underlying will be discussed in detail. Secondly, the effect of spin-polarized current on the magnetic phases of FeRh will be addressed [6][7]. It is understood that the magnetic phase transition of FeRh is a result of the subtle valance of AFM and FM interactions between Fe and Rh moments and itinerant electrons. This indicates that injecting spin-polarized electrons into FeRh would modulate the balance of the interactions, leading to a possible AFM-FM transition. Our resistivity measurement of a sub-micron FeRh wire at the Co/FeRh junction shows that the resistivity is significantly decreased in the AFM phase under spin injection condition, hence demonstrating that spin-polarized current induces AFM-FM phase transition in FeRh. The effect of the spin-polarized current injection is discussed based on possible spin accumulation and spin transfer torque effect at the Co/FeRh interface. Finally, our recent results on spin wave propagation in FM FeRh, which can be integrated into magnonic devices for low energy information transmission applications, will be presented, where we find spin waves propagate over 50 m in FeRh at room temperature [8]. 

[1] T. Taniyama, E. Wada, M. Itoh, and M. Yamaguchi, NPG Asia Mater. 3, 65 (2011). 

[2] T. Moriyama, N. Matsuzaki, K. -J. Kim, I. Suzuki, T. Taniyama, and T. Ono, Appl. Phys. Lett. 107, 122403 (2015). 

[3] I. Suzuki, Y. Hamasaki, M. Itoh, and T. Taniyama, Appl. Phys. Lett. 105, 172401 (2014). 

[4] I. Suzuki, M. Itoh, and T. Taniyama, Appl. Phys. Lett. 104, 022401 (2014). 

[5] T. Taniyama, J. Phys.: Condens. Matter 27, 504001 (2015). 

[6] T. Naito, I. Suzuki, M. Itoh, and T. Taniyama, J. Appl. Phys. 109, 07C911 (2011). 

[7] I. Suzuki, T. Naito, M. Itoh, and T. Taniyama, Appl. Phys. Lett. 107, 082408 (2015). 

[8] T. Usami, I. Suzuki, M. Itoh, and T. Taniyama, Appl. Phys. Lett. 108, 232404 (2016).


Tomoyasu Taniyama is an associate professor in the Laboratory for Materials and Structures, Institute of Innovative Research at Tokyo Institute of Technology, Japan. He obtained his PhD degree from Keio University, Japan, in 1997 for his work on the magnetic properties of transition metal nanoparticles. Prior to his appointment at the Laboratory for Materials and Structures, he worked with Professor J.A.C. Bland at the Cavendish Laboratory, University of Cambridge and with Dr. I. Nakatani at the National Research Institute for Metals (currently National Institute for Materials Science, NIMS), Japan each for 2 years. Also, he was an assistant professor at the Department of Innovative and Engineered Materials, Tokyo Institute of Technology for 6 years. 

Professor Taniyama is at the forefront of spin related physics and engineering in magnetic nanostructures and is investigating novel magnetic properties and spin polarized electron transport phenomena in magnetic thin films and nanostructures, including ferromagnet/semiconductor heterostructures and multiferroic ferromagnet/ferroelectric heterostructures. In particular, he is exploring the fundamental electron spin dependent transport processes and magnetoelectric coupling which underpin the emerging field of spintronics and is a pioneer in the development of nanomagnetism. 

The scientific excellence of Professor Taniyama is recognized as several awards, including the Young Scientists' Prize, the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology in 2005, International Conference on Ferrites 11 (ICF 11) New Product & Novel Technology Award in 2013, and 13th Joint MMM-Intermag Best Poster Award in 2016. He published more than 200 articles in international journals, including Nature Physics, NPG Asia Materials, Physical Review Letters, Physical Review X, Physical Review B, Applied Physics Letters, and Journal of Applied Physics. Also, he currently serves as an Associate Editor of NPG Asia Materials, Springer Nature.

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