MRAM breakthrough

By utilising magnetic random-access memory (MRAM), computers would retain their data during power loss and hard drives the size of a coin could store over 100 films.

The current challenge, however, is the design of a fast, reliable and inexpensive way to build stable and densely packed magnetic memory cells.

A team of researchers at The Johns Hopkins University, writing in the current issue of Physical Review Letters, has come up with one possible answer: tiny, irregularly shaped cobalt or nickel rings that can serve as memory cells.

These "nanorings" can store a great quantity of information. They are also immune to the problem of "stray" magnetic fields, which are fields that "leak" from other kinds of magnets and can interfere with magnets next to them.

"It's the asymmetrical design that's the breakthrough, but we are also very excited about the fast, efficient and inexpensive method we came up with for making them," said paper co-author Frank Q. Zhu, a doctoral candidate in the Henry A. Rowland Department of Physics and Astronomy in the Krieger School of Arts and Sciences at Johns Hopkins.

The nanorings are extremely small, with a diameter of about 100 nanometres. A single strand of human hair can hold 1 million rings of this size, Zhu says.

The asymmetrical design allows more of the nanorings to end up in a so-called "vortex state," meaning they have no stray field at all. With no stray field to contend with, Zhu's team's nanorings can be packed together extremely densely. As a result, the amount of information that can be stored in a given area is greatly increased.

Fabrication of the nanorings is a multistep procedure involving self-assembly, thin film deposition and dry etching. The key to creating the irregular rings, Zhu said, is to - while etching the rings with an argon ion beam at the end of the process - tilt the substrate on which the rings are formed.

"In our previous study, we found that 100 nanometre symmetric nanorings have only about a 40 percent chance to get vortex state," Zhu said. "But the asymmetric nanorings have between a 40 percent and 100 percent chance to get vortex state. This chance can be controlled on-demand by utilising the direction of magnetic field."