(Nanowerk News) Twistronics is not a new dance move, exercise equipment, or new music trend. No, it’s way cooler than all of that. This is an exciting new development in quantum physics and materials science in which van der Waals materials are stacked in layers, like sheets of paper in reams that can be easily twisted and rotated while remaining flat, and quantum physicists have used these stacks to discover quantum phenomena. which are interesting.
Adding to the concept of quantum spin with a two-layer twisted double antiferromagnet, it is possible to have tunable moiré magnets. It represents a new class of material platforms for the next step in twistronics: spintronics. This new science could lead to promising memories and spin-logic devices, opening the world of physics to new avenues with spintronic applications.
A team of quantum physics and materials researchers at Purdue University have introduced twist to control the degree of freedom of spin, using CrI3, a van der Waals (vdW) material coupled with interlayer antiferromagnetism, as the medium. They have published their findings in Natural Electronics (“electrically adjustable moiré magnets in two twisted layers of chromium triiodide”).
“In this study, we fabricated a bent double bilayer CrI3, that is, a double layer plus a double layer with a twist angle between them,” says Dr. Guanghui Cheng, one of the main authors of the publication. “We report moiré magnetism with a rich magnetic phase and significant tunability with the electrical method.”
“We stack and twist the antiferromagnet onto itself and voila you get a ferromagnet,” said Chen. “It is also a striking example of the ‘twisted’ or moiré magnetic areas that have recently appeared in twisted 2D materials, where the twist angle between the two layers exerts a strong tuning knob and changes material properties dramatically.”
“To make the CrI double bilayer bend3we tore off one part of the CrI bilayer3, rotate and stack to other pieces, using what’s called the tear and stack technique,” explains Cheng. “Through measurements of the magneto-optical Kerr effect (MOKE), which is a sensitive tool for investigating magnetic behavior down to multiple atomic layers, we observed the coexistence of ferromagnetic and antiferromagnetic orders, which is a hallmark of moiré magnetism, and further demonstrated voltage-assisted magnetic switching. Such moiré magnetism is a new form of magnetism featuring spatially varying ferromagnetic and antiferromagnetic phases, alternating at regular intervals according to the moiré superlattice.”
Twistronics to date has primarily focused on modulating electronic properties, such as twisted two-layer graphene. The Purdue team wanted to introduce twist to spin degrees of freedom and chose to use CrI3, vdW interlayer-antiferromagnetic-coupled material. The result of self-twisting antiferromagnet stacks is possible by fabricating samples with different twisting angles. In other words, after fabrication, the twist angle of each device is fixed, and then the MOKE measurement is performed.
The theoretical calculations for this experiment were carried out by Upadhyaya and his team. This provides strong support for the observations made by Chen’s team.
“Our theoretical calculations have revealed a rich phase diagram with non-collinear phases from TA-1DW, TA-2DW, TS-2DW, TS-4DW, etc.,” said Upadhyaya.
This research folded into an ongoing research avenue by Chen’s team. This work follows several related recent publications by the team regarding the new physics and properties of “2D magnets”, as in another paper, which was recently published in Nature Communications (“The emergence of electric field-tunable interfacial ferromagnetism in 2D antiferromagnetic heterostructures”). This line of research has interesting possibilities in the fields of twistronics and spintronics.
“The identified moiré magnets represent a new class of material platforms for spintronics and magnetoelectronics,” said Chen. “The observed voltage-assisted magnetic switching and magnetoelectric effects could lead to promising spin memory and logic devices. As a new level of freedom, twist can be applied to a wide variety of homo/heterobilayers of vdW magnets, opening up opportunities for pursuing new physics as well as spintronic applications.”