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Giant magnon spin wave conductance in ultrathin insulators surprises researchers

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The conductivity of giant magnetic waves in thin insulators surprises researchers

The current (I) through the injector electrode generates magnetons in the YIG thin layer. These flow towards the detector electrode, where they produce a voltage (V). Credit: Groningen University / Xiangyang Wei

When you make conductive wires thinner, their electrical resistance increases. This is Ohm’s Law, which is generally true. An important exception is extremely low temperatures, where the mobility of electrons increases when wires become too thin to be effectively two-dimensional. Now, physicists at the University of Groningen, along with colleagues at the University of Brest, have noticed that something similar is happening with conduction of magnetons, spin waves that travel through magnetic insulators, much like the wave through a stadium. The increase in conductivity was staggering, and occurred at ambient room temperature. This note was posted on nature materials On September 22.

Electrons have a magnetic moment called spin, which has an “up” or “down” value. It is possible to synthesize one type of spin by sending a current through a heavy metal, such as platinum. When those spins carried by electrons encounter YIG (yttrium iron garnet) magnetic insulator, the electrons cannot pass through. However, at the interface with YIG, spin excitation is passed on: magnetons (which can also carry spin) are excited. This spin wave passes through the magnetic insulator like a wave in pitch: none of the electrons (“spectators”) move out of place, but nonetheless transmits the spin excitation. The reverse process occurs at the detector electrode: the magnetons make an electronic spin, which then produces a measurable voltage, explains Bart van Weiss, professor of applied physics at the University of Groningen who specializes in fields such as dental electronics.

Motivated by the increased electron mobility in 2D materials, his group decided to test the magnetron transfer in ultrathin (nanometer) YIG films. “These films are not strictly two-dimensional materials, but when they are thin enough, the films can move in only two dimensions,” explains Van Weiss. Measurements made by Ph.D. Student Xiangyang Wei produced a surprising result: the spin conductivity increased by three orders of magnitude, compared to the bulk YIG material.

Dramatic Effects

Scientists don’t use terms like “colossus” lightly, but in this case, it was completely justified, says Van Wess. “We made the material 100 times thinner, and the magnetic conductivity went 1,000 times. This did not happen at lower temperatures, as is required for high electron mobility in 2D conductors, but at room temperature.” This result was unexpected and hitherto unexplained. Van Wees: “In our paper, we present an initial theoretical explanation based on the transition from 3D to 2D magnon transfer. But this cannot fully explain the dramatic effects we observe.”

So what can be done with this giant singer-contact? “We don’t understand it,” says Van Weiss. “Therefore, our current claims are limited. This enables research that may point the way to some undiscovered new physics. In the long run, this may result in new devices as well.” First author Xiangyang Wei adds: “Because there is no electron transfer, magnon waves do not produce any conventional heat dissipation. Heat production is also a major problem in smaller electronic devices.”

superconductivity

Since magnons are bosons (that is, they have integer spin quantum values), it may be possible to create a coherent state comparable to Bose-Einstein condensation. Van Wees: “This may even result in spin superconductivity.” All this for the future. Currently, the giant magnetic conductivity of YIG is well documented. “The measurements are clear, and we look forward to a good collaboration between theoretical and experimental physicists.”

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more information:
X.-Y. Wei et al, Giant spin conductivity of magnons in very thin ferrous yttrium garnet films, nature materials (2022). DOI: 10.1038 / s41563-022-01369-0

Presented by the University of Groningen

the quote: Magnificent Spin-Wave Giant Conductivity in Thin Insulators Surprises Researchers (2022, Sep 23) Retrieved on Sep 23, 2022 from

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