Unit name:Nano Spin

Key words: spintronics, magnetic record, energy saving, element strategy

        Electrons have a nature called “spin.” Depending on the direction (upward or downward) and the number of electron spins, elements, such as iron (Fe), express magnetism. The research field which utilizes both spin and electric charge by techniques of engineering is called “spintronics,” one of the fields of solid state physics. Our research unit is aimed at creating new characteristics through precise regulation of the ultrafine field, and at creating new materials though control of electric current and resistance or, conversely, through control of spins by means of electric current. The members constituting this unit include those conducting research on high temporal resolution measurement of magnetization reversal, semiconductor-spin binding, theoretical spin conduction, or magnetic film formation. Thus, this unit has wide coverage, ranging from basic to applied fields.

Application to magnetic recording media

Fig. 1: An example of patterning by ion irradiation to highly magnetic spinel material. (Magnetic force micrograph) Kr ion applied to the magnetite film, to make it nonmagnetic (the bright part).

        Hard disks, which are familiar in our daily lives, are based on magnetic materials. Conventional hard disks with magnetism in the In-plane direction had a bit size of about 100 nm^□, but the recently developed vertical recording hard disks, have magnetism perpendicular within the plane, with a bit size approaching the order of 100 nm^□. With such ultrafine (ultrahigh density) hard disks, magnetization can fluctuate under the influence of thermal energy (even at room temperature), leading to errors. To achieve stable functioning under such extreme conditions, research and development covering the fundamental aspects of processes is needed. As far as materials for preparation of hard disks are concerned, disks made of ferrite, without using any precious metals, are now being considered. Regarding the processes, utilization of material’s self-organization, application of ion irradiation technology, and so on are now being considered. At our unit, Co ferrite (CoFe₂O₄), which has sufficient performance as a recording material, has been developed to replace the currently used CoCrPt alloy and the Pt-based materials (FePt alloy, etc.), and are now considered next-generation materials.

Fig. 1 illustrates the magnetite (Fe₃O₄) film after Kr ion irradiation. The bright part is nonmagnetic, indicating that this technique enables bit patterning of spinel ferrite. This film at the research stage has a too large pattern size, and it is necessary to reduce the pattern size, and to select a more appropriate material, so that a commercially applicable film can be prepared. To advance such new material development technology to the commercial level, joint R&D with manufacturers with mass production technology is needed.

Medical application of magnetic particles and spintronics

Fig. 2: Magnetic nanoparticles of oval plate form with high heat-generating capability developed for cancer treatment.

        Magnetic recording media are based on film structure. At this unit, attempts have been made to prepare and apply nanoparticles of a lower number of dimensions made of spinning materials. Fig. 2 shows a particle of 20 nm in diameter made of Fe₃O₄. If a guide molecule is added to this particle, the particle can reach specific cells (cancer cells). A possible scene of applying this technology is that cancer cells are burnt completely by the high temperature (heat) locally created by placing the tissue containing this specific particle into a magnetic field. This utilizes the basic principle that placement of a magnetic material in a magnetic field leads to conversion of the generated electric current into heat. Our unit has developed high performance, heat-generating particles capable of generating 1kW heat per g (Fig. 2).

        Our unit members have been conducting research actively also in the field of spintronics, which is expected to develop extensively. Noteworthy outcomes obtained to date pertain to development of a microscope capable of detecting electron spinning of 1/1000 trillion seconds, expected to be useful in exploration of the fundamental principle of magnet movements (Shigekawa Group), semiconductor spintronics aimed at new electronic elements (Kuroda Group), nitride spintronics (Suemasu Group), and theoretical research (Sano Group).

Interviewed on May 1, 2015