Researchers report that they used stacks of ultrathin materials to exert unprecedented control over the flow of electrons based on the direction of their spins — where the electron “spins” are analogous to tiny, subatomic magnets. The materials that they used include sheets of chromium tri-iodide (CrI3), a material described in 2017 as the first ever 2-D magnetic insulator. Four sheets — each only atoms thick — created the thinnest system yet that can block electrons based on their spins while exerting more than 10 times stronger control than other methods.
“Our work reveals the possibility to push information storage based on magnetic technologies to the atomically thin limit,” said co-lead author Tiancheng Song, a UW doctoral student in physics.
Science – Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures
With up to four layers of CrI3, the team discovered the potential for “multi-bit” information storage. In two layers of CrI3, the spins between each layer are either aligned in the same direction or opposite directions, leading to two different rates that the electrons can flow through the magnetic gate. But with three and four layers, there are more combinations for spins between each layer, leading to multiple, distinct rates at which the electrons can flow through the magnetic material from one graphene sheet to the other.
“Instead of your computer having just two choices to store a piece of data in, it can have a choice A, B, C, even D and beyond,” said co-author Bevin Huang, a UW doctoral student in physics. “So not only would storage devices using CrI3 junctions be more efficient, but they would intrinsically store more data.”
The researchers’ materials and approach represent a significant improvement over existing techniques under similar operating conditions using magnesium oxide, which is thicker, less effective at blocking electrons and lacks the option for multi-bit information storage.
“Although our current device requires modest magnetic fields and is only functional at low temperature, infeasible for use in current technologies, the device concept and operational principle are novel and groundbreaking,” said Xu. “We hope that with developed electrical control of magnetism and some ingenuity, these tunnel junctions can operate with reduced or even without the need for a magnetic field at high temperature, which could be a game changer for new memory technology.”
Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.