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Program Aims and Selection Criteria of DL
Shoogo UenoKyushu University/Teikyo University/The University of Tokyo
Biomagnetics is an interdisciplinary field where magnetics, biology and medicine overlap. It has a long history since 1600, when William Gilbert published his book De Magnete. Recent advances in biomagnetics have enabled us not only to detect extremely weak magnetic fields from the human brain, but also to control cell orientation and cell growth by extremely high magnetic fields. Pulsed magnetic fields are used for transcranial magnetic stimulation (TMS) of the human brain, and both high frequency magnetic fields and magnetic nanoparticles have promising therapeutic applications for treatments of cancers and brain diseases such as Alzheimer’s and Parkinson's. On the imaging front, magnetic resonance imaging (MRI) is now a powerful tool for basic and clinical medicine. New methods of MRI based on the imaging of impedance of the human body, called impedance MRI, and the imaging of neuronal current activities in the human brain, called current MRI, are also being developed.
This lecture focuses on the advances in biomagnetics and bioimaging obtained mostly in our laboratory in recent years. The lecture describes: (1) a method of localized magnetic stimulation of the human brain by TMS with a figure-eight coil; (2) magneto-encephalography (MEG) to measure extremely weak magnetic fields produced from brain electrical activity using superconducting quantum interference device (SQUID) systems; (3) impedance MRI and current MRI; (4) cancer therapy and control of iron-ion release from, and uptake into, ferritin, an iron-storage protein, by using both high frequency and pulsed magnetic fields and magnetic nanoparticles; and (5) magnetic control of biological cell orientation and cell growth by strong static magnetic fields. These new biomagnetic approaches will open new horizons in brain research, brain treatment, and regenerative medicine.
Kevin O'GradyThe University of York
The phenomenon of exchange bias has remained something of a mystery since it was discovered in core-shell particles in 1956 . Over the subsequent years many different models have been proposed to explain this effect, most of which agree with some experimental data that can be found in the literature. No single theory, however, has been able to explain the data consistently for different systems.
In this lecture the reason for our inability to explain exchange bias will be reviewed, and a new paradigm to explain the phenomenon in sputtered polycrystalline films will be presented. This new paradigm is based on an original granular model described by Falcomer and Charap . Its premise is that very careful thermal and magnetic cycling is required to ensure that the order in the antiferromagnetic grains is controlled. Without such careful control, reproducible data cannot be obtained.
These time-consuming and complex measurement procedures, to which we refer as the York protocol, have been developed over the last 9 years. Using the York protocol and an extension of the former granular model, effects such as the film thickness dependence and grain size dependence of exchange bias can be fully explained with an excellent fit between theory and experiment . The York protocol also allows for the measurement of the anisotropy constant of antiferromagnetic grains . This model provides an understanding of the behavior of the individual antiferromagnetic grains in detail. Since the behavior of the "bulk" of the antiferromagnetic grains is now known, preliminary data describing the behavior of the interface spins can now be distinguished from the behavior of the bulk. Possible mechanisms for the behavior of the interfaces themselves will also be presented.
 W. H. Meiklejohn and C. P. Bean, Phys. Rev., vol. 102, pp. 1413-1414, June 1956; IEEE Trans. Magn., vol. 37, pp. 3866-3876, November 2001. E. Fulcomer and S. H. Charap, J. Appl. Phys., vol. 43, pp. 4190-4199, October 1972. G. Vallejo-Fernandez, L. E. Fernandez-Outon, and K. O’Grady, J. Phys. D: Appl. Phys., vol. 41, 112001, June 2008. G. Vallejo-Fernandez, L. E. Fernandez-Outon, and K. O’Grady, Appl. Phys. Lett., vol. 91, 212503, November 2007.
Claudia FelserJohannes Gutenberg Universitat Mainz
Tremendous progress has been made recently in the development of magnetic Heusler compounds specifically designed as materials for spintronic applications . While problems in the field of spintronics remain, the use of half-metallic Heusler compounds provides a prospect for novel solutions.
Heusler compounds can be made with high spin polarization and high Curie temperature as well as high spin injection efficiency, either very low or high damping, tunable magnetic moment (low and high magnetic moments can be realized), and tunable anisotropy. There is, therefore, great potential that many materials-related problems present in current-day 3d metal systems can be overcome.
The handling of interfaces with respect to their chemical properties (atomic diffusion and roughness), electronic properties (e.g., Schottky barrier design), and spin properties (injection and pumping) remains a big challenge. The potential exists for new phenomena and applications with the use of novel materials in the Heusler compound family - for example, the use of semi-conducting Heusler compounds as non-ferromagnetic spin conductors.
High spin polarization and high Curie temperatures were found in Co2-Heusler compounds, with Curie temperatures up to 1120 K in Co2FeSi. Mn2YZ compounds (Y = Mn, Cr; Z = Al, Ga, Si, Ge, Sb) such as Mn3Ga are ferrimagnets with low magnetic moments despite their high Curie temperatures. Due to the Jahn Teller instability of manganese in these materials, some of them show a tetragonal distortion, which renders out-of-plane magnetization in thin films possible. Semiconducting half-Heusler compounds such as TiNiSn have attracted attention as potential candidates for thermoelectric applications. These complex C1b compounds can be designed as n- and p-type thermoelectrical materials with exceptionally large figure of merit, ZT≈1.5 at high temperatures.
The potential for applications of these ternary compounds as rationally designed, multifunctional materials will be discussed.
 C. Felser, G. H. Fecher, and B. Balke, Angew. Chem. Int. Ed., vol. 46, pp. 668-699, January 2007.
E. Dan DahlbergUniversity of Minnesota
One of the current frontiers in magnetism is to understand the domain structure and the magnetization reversal in nanometer-sized particles. Explorations at these length scales have been aided by the development of new magnetic imaging techniques , one of which is the magnetic force microscope (MFM), a variant of the atomic force microscope. We have utilized the high resolution MFM (30 nm) we developed  to increase our fundamental understanding of magnetism on this length scale. I will discuss the field-induced magnetic reversal in particles on the order of hundreds of nanometers in width and about twice that in length. In general, for the small aspect (length to width) ratio, the magnetization reverses by the formation of a single vortex and its propagation down the length of a particle (when the fields are applied perpendicular to the long axis). There are some surprises when the aspect ratio of the particles increases.
 E. Dan Dahlberg and Jian-Gian Zhu, Physics Today, vol. 48, pp. 34-40, April 1995.  George D. Skidmore, Sheryl Foss, and E. Dan Dahlberg, Appl. Phys. Lett., vol. 71, pp. 3293-3295, December 1997.