Atoms and Energy

Hideo Kaiju

Nanostructured Spintronics Devices

Hideo Kaiju , Associate Professor

Green Nanotechnology Research Center, RIES

High school : Seijo High School (Tokyo)

Academic background : Graduate School of Science and Technology, Keio University

Research areas
Materials Science, Magnetic Engineering
Research keywords
Spintronics, Nanoscale Junctions, Energy Saving

What is the Goal of Your Research?

Figure 1  Spintronics

Electronics is essential technology for modern society. For example, home electric appliances, such as television sets and audio devices, and information and communication equipment, such as personal computers and smartphones, were created based on the chronological development of electronics. In this electronics world, the electric charge that an electron has within a substance is used for controlling information. On the other hand, an electron within a substance has spin, which is another degree of freedom. The spin is the rotation of an electron and is also known as a source of magnetism. Recently, spintronics, an entirely new field of research that combines spin and electronics, has been attracting a lot attention all over the world (Figure 1). This is because spintronics can help create new functional and high-performance devices that cannot be realized by conventional electronics. Spintronics has evolved significantly in the last dozen years. One of the most famous phenomena of spintronics is the giant magnetoresistance (GMR) effect, where electric resistance changes significantly when an external magnetic field is applied. Dr. Grünberg and Dr. Fert received the Nobel Prize in Physics for discovering this phenomenon in 2007. This GMR effect discovery triggered more investigation that resulted in the discovery of a tunnel magnetoresistance (TMR) effect, which is a magnetoresistance effect with even higher sensitivity. Today, the TMR effect is applied to the magnetic head in a computer hard disk drive (HDD) and highly sensitive magnetic field sensors. It is expected that various new phenomena will be discovered in the field of research on spintronics and meanwhile new functional devices will be created. I am one of the researchers who are fascinated with the spintronics world. I am conducting research every day to try and discover a new phenomenon and create a new functional device.


What Kind of Research are You Conducting?

Figure 2  Nanoscale junction device using magnetic thin film edge

In order to create new spintronics devices, I am currently researching nanoscale junction devices that use a thin magnetic film edge as shown in Figure 2. In this device, a molecule or oxide insulator is sandwiched between the edges of the thin films. This structure includes magnetic thin films with their edges crossing each other at right angles, and therefore the junction area (S=dxd) depends on the thickness (d) of the thin magnetic film. For example, when the thickness of the thin magnetic film is one to twenty five nanometers, an ultrafine nanoscale junction having a junction area of 1x1 to 25x25 square nanometers can be created. Using this nanoscale junction, new nanoscale conduction of a molecule or oxide insulator and its spin conduction can be clarified. Actually, we have successfully fabricated an ultrafine junction device having a junction size of about ten nanometers and observed a quantum-mechanical tunnel effect and nanoscale molecular conduction.


What Kind of Devices do You Use and What Kind of Experiments do You Conduct?

Figure 3  High vacuum evaporation machine for device fabrication

Figure 4 Focused MOKE measurement system, which can observe spin states using light.

To create a nanoscale junction device that I am proposing, I am using a vacuum evaporation machine for fabricating magnetic thin films and molecular films, a compression bonder for bonding glass substrates, a chemical mechanical polisher for polishing the edge of the magnetic thin film, etc. Figure 3 shows experimental equipment that can make, etch and perform compression bonding of molecular films in the same vacuum chamber. This experimental equipment was researched and co-developed with a company in a government sponsored project.

To evaluate the device that was developed, we used an atomic force microscope that observes the surface conditions, a transmission electron microscope that analyzes the internal structure, an AC/DC four-terminal device that measures the electric conduction properties, a magnetic force microscope and a focused magneto-optical Kerr effect (MOKE) measurement that investigates the magnetic properties, etc. The focused MOKE measurement system shown in Figure 4 can observe spin states using light.


What Will be Your Next Goal?

With a spintronics device that has a nanoscale junction, we expect to shed light on various new phenomena such as the giant magnetoresistance effect, the spin filter effect, the switching effect, etc. We hope to discover and use these new phenomena to create super energy saving devices and devices with a low environmental impact.