Frequency characteristics of the tunneling magnetocapacitance ratio (blue dots) and tunneling magnetoresistance ratio (red squares). The solid lines represent the results of the theoretical calculation using the Debye-Fröhlich model. Experimental and calculated results are closely matched.

**Key Points**

* Achieved the world’s highest tunneling magnetocapacitance ratio in a magnetic tunnel junction.* Mechanism of the tunneling magnetocapacitance effect clarified with new theoretical calculation using the Debye-Fröhlich model.

* Tunneling magnetocapacitance ratio exceeding 1000% at room temperature expected with theoretical calculation.

**Overview**

Associate Professor Hideo Kaiju and Professor Junji Nishii of Research Institute for Electronic Science (Director: Professor Junji Nishii) at Hokkaido University, Associate Professor Taro Nagahama of the University’s Faculty of Engineering, and Professor Gang Xiao of Brown University’s Physics Faculty have succeeded in room temperature observation of the world’s highest tunneling magnetocapacitance ratio (155%) in a magnetic tunnel junction1comprised of a layered structure of ferromagnet-insulator-ferromagnet. The mechanism of the tunneling magnetocapacitance effect2 has at last been clarified with a new theoretical calculation using the Debye-Fröhlich model3. This theoretical calculation has clarified that a tunneling magnetocapacitance ratio in excess of 1000% can be expected at room temperature. These results provide new academic knowledge on AC spin dynamics, and can be expected to lead the way to a new direction in design for creation of the next generation of innovative, super-performing, and low power consumption memory devices and ultra-high sensitivity magnetic sensors.

This research was conducted with the assistance of Grant-in-Aid for Scientific Research – Scientific Research (B) No.15H03981, and Brown University’s National Science Foundation through Grant No.DMR-1307056.

**Terms**

1 Magnetic tunnel junction：

An extremely thin insulator is sandwiched between two ferromagnetic layers to form what is referred to as a ‘magnetic tunnel junction’. When the thickness of the insulator is in the order of nanometers, a current flows due to quantum mechanical effects (tunneling effects).

2 Tunneling magnetocapacitance effect：

When magnetization of the two ferromagnetic layers is parallel in the magnetic tunnel junction, capacitance increases, and decreases when magnetization is anti-parallel. There are generally two types of magnetocapacitance. One has been discovered in multiferroic materials, and the other in spintronics devices as represented by magnetic tunnel junctions (Scientific Reports 5, 13704 (2015)).

3 Debye-Fröhlich model：

A very effective theoretical model for calculation of the dynamic dielectric constant. A quantitative understanding was reached last year with a system of magnetic nano-particles distributed in an insulator (Nature Communications 5, 4417 (2014)).