IEEE TRANSACTIONS ON MAGNETICS, VOL. 51, NO. 10, OCTOBER 2015 0800511 Advances in Magnetics Roadmap for Emerging Materials for Spintronic Device Applications Atsufumi Hirohata 1 , Hiroaki Sukegawa 2 , Hideto Yanagihara 3 , Igor Žuti´ c 4 , Takeshi Seki 5 , Shigemi Mizukami 6 , and Raja Swaminathan 7 1 Department of Electronics, University of York, York YO10 5DD, U.K. 2 Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047, Japan 3 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8577, Japan 4 Department of Physics, University at Buffalo–The State University of New York, Buffalo, NY 14260 USA 5 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 6 WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 7 Intel Corporation, Chandler, AZ 85226 USA The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used, for example, as a cell for a magnetic random access memory and a spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarized electrons efficiently into a nonmagnet. We have accordingly identified two key properties to be achieved by developing new magnetic materials for future spintronic devices: 1) half-metallicity at room temperature (RT) and 2) perpendicular anisotropy in nanoscale devices at RT. For the first property, five major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: 1) Heusler alloys; 2) ferrites; 3) rutiles; 4) perovskites; and 5) dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level E F only for its minority spins, achieving 100% spin polarization at E F . We have also evaluated L1 0 alloys and D0 22 –Mn alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarization. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations, and interdisciplinary applications within 35 years time scale. The individual analyses and the projections are discussed in the following sections. Index Terms— Half-metallic ferromagnets, magnetic anisotropy, magnetic materials, spintronics. I. HEUSLER ALLOYS H EUSLER alloys are ternary alloys originally discovered by Heusler [1]. He demonstrated the ferromagnetic behavior in an alloy consisting of nonmagnetic (NM) atoms, Cu 2 MnSn. Since then, these alloys have been investigated due to their properties of shape memory and thermal conductance. In 1983, de Groot et al. [2] reported the half-metallic ferro- magnetism in one of the Heusler alloys, half-Heusler NiMnSb alloy. A great deal of effort has accordingly been devoted to achieve the half-metallicity at room temperature (RT) using a Heusler alloy. In particular, Block et al. [3] measured a large tunneling magnetoresistance (TMR) in bulk full-Heusler Co 2 (Cr, Fe)Si alloy, followed by a similar measurement in a thin-film form [4]. Among these Heusler alloys, Co-based full-Heusler alloys are the most promising candidates to achieve the RT half-metallicity due to their high Curie temperature Manuscript received October 23, 2014; revised June 26, 2015; accepted June 29, 2015. Date of publication July 16, 2015; date of current ver- sion September 16, 2015. Corresponding author: A. Hirohata (e-mail: atsufumi.hirohata@york.ac.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2015.2457393 Fig. 1. Minority-spin bandgap [7] and L 2 1 phase [6] of the full-Heusler alloys. (T C ≫ RT), good lattice matching with major substrates, large minority-spin bandgap (≥0.4 eV, see Fig. 1), and large magnetic moments in general [≥4 μ B per formula unit (f.u.)] [5], [6]. The main obstacle to achieve the half- metallicity in the Heusler-alloy films is the vulnerability against the crystalline disorder, such as the atomic displacement, misfit dislocation, and symmetry break in the This work is licensed under a Creative Commons Attribution 3.0 License. For more information, see http://creativecommons.org/licenses/by/3.0/