Precision Interfacial Control Enables Development of Magnetic Tunnel Junction with the Highest Tunnel Magnetoresistance.

The National Institute for Materials Science (NIMS) achieved a tunneling magnetoresistance (TMR) of 631% at room temperature, breaking the previous world record, which had stood for 15 years.

The research team achieved this by tuning the interfaces at a magnetic tunnel junction (MTJ). MTJ showed a very large oscillatory effect in the TMR ratio with a peak-to-valley (PV) variation of 141%. This phenomenon may be exploitable to dramatically increase the sensitivity of magnetic sensors and the capacity of antiferromagnetic random access memory (MRAM).

This research has been published online at Applied Physics Letters.

Tunnel magnetoresistance (TMR) is a dramatic change in the tunneling current in the MTJ—which consists of two ferromagnets separated by a thin insulator—when the relative magnetizations of the two magnetic layers change in alignment. This effect has been used in micro and highly sensitive magnetic sensors and energy efficient MRAM.

The sensor sensitivity and MRAM density can be increased by using MTJs that are capable of producing larger TMR ratios (eg, the differences in electrical resistance caused by the MTJ when the magnetization direction of two ferromagnets is switched between parallel and antiparallel).

The room temperature percentage of 604% recorded in 2008 remained a world record until recently. As this record has been distinguished for years, it is widely believed that there is still little room for improvement in magnetic sensor performance and MRAM performance.

This NIMS research team recently broke this TMR ratio record by precisely controlling the interfaces in the MTJ composed of two thin magnetic layers separated by a thin dielectric layer. The team made atomic-scale modifications to the MTJ, including fabricating all components of its layer from single crystals and adding an ultra-thin metallic magnesium layer between the magnetic and insulating layers. As a result, the team was able to create an MTJ with a maximum TMR of 631%.

In addition, the TMR ratio of this MTJ was found to oscillate with a PV difference of 141%—much larger than the PV difference in extant MTJs (up to a few tens of percent). This result was consistent with the previous finding that the variation of the photovoltaic oscillation of the TMR is significantly affected by the thickness of the insulating layer.

In future research, the team will work to shed light on the little-understood relationship between TMR ratios and the photoelectron oscillation difference by investigating the mechanisms underlying the large photoelectron difference observed in this paper. This understanding may enable the team to break the world record for the ratio of room temperature to TMR.

Using this amazing result, the team will accelerate the development of ultra-sensitive magnetic sensors for medical use and very large-capacity MRAM.

This project was carried out by a research team led by Thomas Scheike (private researcher, Center for Research in Magnetic and Spintronic Materials (CMSM), NIMS) and Hiroaki Sukegawa (group leader, CMSM, NIMS).