Tiny amounts of heat can be used to control the movement of magnetic vortices called skyrmions, physicists at RIKEN have shown.1. This ability could help develop energy-efficient forms of computing that harness waste heat.
Skyrmions are tiny vortices that form when the magnetic flux of a group of atoms organizes into swirling patterns. Skyrmions can move within a material, and under certain conditions, they group together to form a regular arrangement known as a skyrmion network (top part of Figure 1).
Skyrmions are promising information carriers in new generation computer chips which require very low power consumption. Researchers can already control skyrmions by applying electric currents and magnetic fields, but instead seek to manipulate them using a flow of heat. “This is an exciting prospect because it would increase the possibility of using waste heat to move skyrmions,” says Xiuzhen Yu of the RIKEN Center for Emergent Matter Science.
Now Yu and his colleagues have shown how a temperature gradient can be used to propel skyrmions through an electrically insulating magnetic material.
The team built a device that consisted of a plate of this material, a miniature heating element, and two electric thermometers. They then generated skyrmions about 60 nanometers wide in the plate by cooling it to about -253 degrees Celsius and applying a magnetic field. These skyrmions came together in a stable honeycomb structure known as the hexagonal skyrmion network.
Yu’s team then slightly increased the temperature at one end of the plate and used a transmission electron microscope to observe how it affected the skyrmions. A temperature gradient of 100 degrees per millimeter of plate was sufficient to set the skyrmions in motion. Above this threshold, the edge of the honeycomb network drifted from the colder end to the hottest end of the plate, moving in the opposite direction to the heat flow (lower part of figure 1). This required a very low heat output of just 10 microwatts, which is hundreds or thousands of times smaller than the power needed to move skyrmions using electric currents or magnetic fields. Using slightly higher power, individual skyrmions could be dragged through the plate by the temperature gradient.
The researchers say this is the first time that heat-driven skyrmion motion has been observed in an insulating magnet. “This discovery should prompt researchers to develop energy efficient devices using skyrmions,” Yu said.
The team is now studying the heat-induced dynamics of skyrmions, including their transformation into their anti-particle-anti-skyrmions in metallic systems at room temperature.