Using Berry Phase Monopole Engineering for High Temperature Spintronics Devices

Spintronic devices are electronic devices that use electron spin (an intrinsic form of angular momentum possessed by the electron) to achieve high-speed processing and low-cost data storage. In this regard, spin transfer torque is a key phenomenon that makes it possible to achieve ultrafast, low-power spintronic devices. However, recently, spin-orbit torque (SOT) has emerged as a promising alternative to spin transfer torque.

Many studies have investigated the origin of SOT, showing that in non-magnetic materials, a phenomenon called spin Hall effect (SHE) is essential for obtaining SOT. In these materials, the existence of a “Dirac band” structure, a specific arrangement of electrons in terms of energy, is important to achieve significant SHE. Indeed, the Dirac band structure contains “hot spots” for the Berry phase, a quantum phase factor responsible for intrinsic SHE. Thus, materials with appropriate Berry phase hot spots are essential for SHE engineering.

In this context, the material tantalum silicide (TaSi₂) is of great interest because it has several Dirac points close to the Fermi level in its band structure, suitable for the practice of Berry phase engineering. To demonstrate this, a team of researchers, led by Associate Professor Pham Nam Hai from the Department of Electrical and Electronic Engineering at Tokyo Institute of Technology (Tokyo Tech), Japan, recently studied the influence of hotspots of the Dirac strip on the temperature dependence of ELLE at TaSi₂.

“Berry phase monopole engineering is an interesting research avenue because it can give rise to efficient high-temperature SOT spintronic devices such as magnetoresistive random access memory,” explains Dr. Hai. Their findings were published in the journal Applied physics letters.

Through various experiments, the team observed that the SOT efficiency of TaSi₂ remained almost unchanged from 62 K to 288 K, which was similar to the behavior of conventional heavy metals. However, by further increasing the temperature, the SOT efficiency suddenly increased and almost doubled at 346 K. Moreover, the corresponding SHE also increased similarly.

This behavior was notably very different from the behavior of conventional heavy metals and their alloys. After further analysis, the researchers attributed this sudden increase in SHE at high temperatures to Berry phase monopoles.

“These results provide a strategy to improve the efficiency of high-temperature SOT via Berry phase monopole engineering,” explains Dr. Hai.

Their study highlights the potential of Berry phase monopole engineering to efficiently utilize SHE in non-magnetic materials and opens a new avenue for the development of high-temperature, ultrafast, low-power SOT spintronic devices.