Scientists reveal new physical mechanisms to manipulate the magnetization of ferromagnets using ultrafast thermal conductance

Recently, scientists at the University of Illinois at Urbana-Champaign revealed a new physical mechanism by which scientists can use heat to manipulate the formation of magnetism. Unlike traditional magnetic fields, the new mechanism relies on thermal energy transmission, providing a new way to manipulate magnetization at the nanoscale. Related papers were published in the recently published Nature and Physics.

According to a report by the Physicist Network on the 8th, the researchers made a multi-layer metal spin valve structure consisting of two magnetic layers and a heat transfer layer. “When heat flows through the first layer of magnetic material, electron spin separation occurs. Our research uses this. With this process of forming a magnetic bipolar flow, we can manipulate the direction of the second magnetic layer.” Champagne Professor David Cassir, head of the Department of Materials Science and Engineering at the branch campus, said.

“We use the spin current caused by ultrafast thermal conduction to generate the spin transfer torque (STT). The spin transfer torque is the transfer of the spin angular momentum of a ferromagnetic body from conduction to magnetization, allowing people to use the spin flow. Instead of a magnetic field to manipulate nano-magnets, Zhou Zhoumin, the first author of the paper and a Ph.D. in materials science and engineering at the school, said. Normally, the use of current through the magnetic layer to produce spin transfer torque, they have now demonstrated a mechanism for generating spin transfer torque with a strong heat flow, which is mainly driven by the spin-dependent Seebeck effect. The Seebeck effect is a thermoelectric phenomenon in which the temperature difference between two different materials in the same circuit produces a voltage. The spin-dependent Seebeck effect is a similar phenomenon produced by spintronics in a ferromagnetic body.

In the metal spin valve configuration, the researchers used a picosecond (one billionth of a second) laser pulse to create a strong ultra-fast heat flow that quantifies the thermal spin transfer. This heat flow reaches 100 GW per square meter (gigawatts, meaning 1 billion watts) for about 50 picoseconds. "The sign and value of the thermally driven spin stream can be controlled by the composition of the ferromagnetic layer and the thickness of the heat transfer layer," says Cassirer.

In nano-spin devices, the coupling of spin and heat creates new physical phenomena, and the spin transfer torque driven by heat transfer provides a new way to manipulate local magnetization. "The physical mechanism of separating electron spins by heat flow is related to thermocouple action and thermal generators," said Cassir. "Thermal generators provide power to deep space detectors. In thermoelectric devices, heat flow causes charge separation. Separation can be used to detect temperature and can also be used to supply power."

In the middle school textbook, the magnet seems to be related only to electricity. In fact, the magnetic phenomenon and the sound and heat can affect each other. This is currently a hot area that attracts many scientists. People have changed their magnets, not only using the old method of "friction, friction", but also using a laser to precisely manipulate a small area to magnetize. In the future, in our household appliances, there will be more sophisticated and complex magnets. It is also possible that a new and exciting application will be created in the fields of navigation and numerical control because of the cutting-edge magnetic technology.

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