• Spin caloritronics

The interaction between heat and the electron’s spin triggered a new research field called spin caloritronics (from ‘calor’, the Latin word for heat). This has brought a new area of fascinating subjects involving the use of heat, which presents ubiquitous and infinite. Specifically, the electrical voltage can be generated via inverse Spin Hall and Spin Seebeck effects from a temperature gradient. This kind of device so-called spin-thermoelectric device was composed of simple layers by layers. Moreover, the output of the spin thermoelectric device is proportional to the area perpendicular to the thermal gradient. This has opened an opportunity to generate electricity with simple and large-area coatings, using cheap materials. Our goals are to obtain high electric output efficiency via compatible industrial fabrication methods such as metal-organic decomposition (MOD) and sputtering techniques.  

• Topological insulators & Weyl Semimetals

Recently, topological insulators (TIs) and Weyl semimetals (WSs) have been discovered as potential materials for spin-orbit torque (SOT) as well as spin thermoelectric (STE) devices due to their high spin to charge conversion efficiency.  It was observed experimentally that the spin Hall angle of TIs and WSs can be 1-2 orders larger than conventional heavy metals such as Pt, W, Ta, and Au... which were typical spin detection materials. Incorporated with PMA (TmIG, EuIG...) or IMA (YIG, GdIG,...) magnetic insulators, numerous spin caloritronic applications can be realized. In our laboratory, we are growing high-quality of BixSb1-x and  WTe2 which are representative TIs and WSs.  Eventually, we would like to use them for high-efficiency SOT and  STE devices.

• Magnetic insulators 

Magnetic insulators (MIs) have emerged as highly promising candidates for numerous applications in the magnetic and optical industries. Among the diverse range of magnetic oxides, garnets have demonstrated exceptional qualities due to their composite diversity and cation arrangements. Consequently, scientists have made considerable efforts in recent years to investigate various types of garnets and their doped compounds. One well-known material is Y3Fe5O12 (YIG), which exhibits the smallest magnetic damping constant (~10^-5) and is well-suited for the field of spintronics. Another material, Tm3Fe5O12 (TmIG), displays out-of-plane magnetic anisotropy, high resistivity, and a prominent Curie temperature, making it ideal for applications in the memory industry. Additionally, Bi3Fe5O12 (BiIG) with a high Faraday rotation angle holds potential for utilization in the magneto-optics and display industry. Moreover, heterostructures comprising MIs and materials with a large magnon diffusion length can be employed in magnon valve structures, which have the potential to be utilized in logical devices like RAM. Recently, our focus has been on fabricating high-quality garnets to study spin dynamics and apply them in practical applications. 

• Active metamaterials

  Meta- (from Greek: μετά = "after", "beyond", "with", "adjacent", "self"), is a prefix used in English (and other Greek-owing languages) to indicate a concept which is an abstraction from another concept, used to complete or add to the latter. Metamaterials are artificial materials engineered to provide properties that may not be readily available in nature such as negative refractive index. For metamaterials with negative permittivity and permeability, several names and terminologies have been suggested, such as left-handed material, double-negative metamaterial, etc. Many research groups are now studying various aspects of this class of metamaterials, and several ideas and suggestions for future applications of these materials have been proposed. The overall goal of our research in this field deals with the development of metamaterials based on magnetic nanocomposites and nanostructured metallic materials from the material point of view.

• Surface plasmon-based nano biosensor materials

  Recently, metallic nanoparticles and nanostructures have been successfully employed as molecular-recognition elements and amplifiers in biosensors, using evanescent electromagnetic fields such as propagating surface plasmon resonance (SPR). The plasmon-induced enhancement of the electromagnetic field near the metal surface has been used extensively in sensors, and more recently also to amplify fluorescence and Raman scattering. In sensor applications, the changes in the plasmonic resonance wavelength of maximum absorption or scattering are monitored as a function of changes in the chemical and physical environment of the surface of the nanoparticles. Here, high sensitivity of the spectral response of the plasmonic resonance absorption band to changes in the refractive index of the surroundings is desired to detect molecules. From the viewpoint of sensitivity, unique metal structures have been at the center of attention. Many theoretical and experimental studies have been made on metal nanopatterns with different geometries to find the best configuration to enhance the sensitivity of the plasmon resonance. The overall goal of our research in this field deals with the development of novel nanomaterials for ultrahigh sensitive biosensors and understanding of underlying physics of nanomaterials.

• Magnetic barcode-based microfluidics for multiplexed high-throughput analysis

  Very recent efforts have concentrated on performing assays in microfluidic flow cells using micron/nano-sized carriers functionalized with biochemical probes. This method allows flexible, automated, high-throughput analysis, whose detection capabilities can be extended simply by increasing the size of the library of probes rather than the number of sites in the microarray. Magnetic bioassays have been proposed and developed based only on the detection of the presence or absence of functionalized micron/nano-sized magnetic beads. A great improvement in bioassay sophistication and speed could be gained by using magnetic carriers and rewritable magnetic tags which encoding a specific signature on each label. Magnetic carriers are unique materials that can be actively controlled using external magnetic fields. Applications include separations for environmental and biomedical applications, magnetically controlled imaging and sensing, and advanced fluidic devices. These allow a high-throughput multiplexed assay to be performed with a single aliquot of the analyte, as the probes on the carriers which successfully hybridize can be unambiguously identified by their encoded labels. The overall goal of our research deals with the Integration of high sensitivity magnetic resistance sensors and rewritable planar multi-bit magnetic tags of complex magnetic nanostructures for realizing the next-generation suspension-type multiplexed high-throughput molecular recognition system.

• Nanostructured spintronic materials

  Magnetic materials have become so promiscuous with their importance in almost all fields of human endeavor such as telecommunication, medical instrumentation, data storage technology, and domestic applications such as security systems, etc. Despite all these achievements, current developments have shown that there are more interesting novel phenomena exhibited by these materials when the dimensions are scaled down to the nanometer regime. Hence, there is a current burst of research interests by several research groups all over the world in fabricating and investigating the properties of magnetic structures with nanometer-scale dimensions. With advances in atomic-scale growth and characterization methods, it is presently possible to fabricate magnetic nanostructures which reveal a host of novel and interesting properties such as perpendicular magnetic anisotropy (PMA), giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), etc. The overall goal of our research is to successfully fabricate nanomagnetic systems scaled down to a few tens of nanometers. Both bottom-up and top-down approaches will be adopted to fabricate various nanomagnetic systems. We are aiming to fabricate less than 30 nm-sized nanodot magnetic arrays of CoCrPt, and FePt alloy films having ultrahigh perpendicular anisotropy, to realize 1 Tbit/in2 data storage.