Nanoscale magnetic media diagnostics by rippling spin waves

April 3, 2012
Trapped beneath the magnetic tip of a microscale cantilever, spin waves can be used to non-destructively measure the properties of magnetic materials and search for nanoscale defects, especially in multilayer magnetic systems like a typical hard drive, where defects could be buried beneath the surface. Credit: McMichael/NIST

Memory devices based on magnetism are one of the core technologies of the computing industry, and engineers are working to develop new forms of magnetic memory that are faster, smaller, and more energy efficient than today's flash and SDRAM memory. They now have a new tool developed by a team from the National Institute of Standards and Technology (NIST), the University of Maryland Nanocenter and the Royal Institute of Technology in Sweden—a method to detect defects in magnetic structures as small as a tenth of a micrometer even if the region in question is buried inside a multilayer electronic device.*

The technique demonstrated at the NIST Center for Nanoscale Technology (CNST) builds on work by researchers at the Ohio State University.** The idea is to trap and image oscillating perturbations of a field—"spin waves"—in a thin film. Trapped spin waves provide scientists with a powerful new tool to nondestructively measure the properties of magnetic materials and search for nanoscale defects that could or have caused memory failures, especially in multilayer magnetic systems like a typical hard drive, where defects could be buried beneath the surface.

According to NIST researcher Robert McMichael, when left alone, the material's magnetization is like the surface of a pond on a windless day. The pond is comprised of smaller magnetic moments that come with the quantum mechanical "spin" of electrons. Tap the surface of the pond with a piece of driftwood, or microwaves in this case, and the surface will begin to ripple with spin waves as the microwave energy jostles the spins, which, in turn, jostle their neighbors.

"The trick we play is to tune the microwaves to a frequency just outside the band where the spin waves can propagate—except right under our magnetic probe tip," says McMichael. "It's like the pond is frozen except for a little melted spot that we can move around to check magnetic properties at different spots in the sample."

The trapped are disturbed by defects in the material, and this effect allows the defects to be characterized on 100 nm length scales.

Previous work had shown this same effect in magnetic spins that were oriented perpendicular to the magnetic film surface, meaning that the individual spins coupled strongly with their neighbors, which limited the resolution. This new work adds the extra feature that the magnetic spins are aligned in plane with one another and are not as tightly coupled. This setup is not only more representative of how many devices would be structured, but also allows for tighter focusing and better resolution.

Explore further: Researchers use spin waves to measure magnetic polarization of electrical current

More information: * H-J. Chia, F. Guo, L.M. Belova and R. D. McMichael. Nanoscale spin wave localization using ferromagnetic resonance force microscopy. Physical Review Letters. 108, 087206 (2012). prl.aps.org/pdf/PRL/v108/i8/e087206

** See Lee et al. Nanoscale scanning probe ferromagnetic resonance imaging using localized modes. Nature. 466, 12. Aug. 12, 2010. doi:10.1038/nature09279

Related Stories

Nanomagnets offer food for thought about computer memories

April 27, 2011

(PhysOrg.com) -- Magnetics researchers at the National Institute of Standards and Technology (NIST) colored lots of eggs recently. Bunnies and children might find the eggs a bit small—in fact, too small to see without ...

Spin pumping effect proven for the first time

September 12, 2011

German physicists led by Prof. Dr. Hartmut Zabel have demonstrated the spin pumping effect in magnetic layers for the first time experimentally. The behaviour of the spin pumping had previously only been predicted theoretically. ...

Team controls thermal fluctuations with spin current

November 17, 2011

(PhysOrg.com) -- A team of researchers from the NIST Center for Nanoscale Science and Technology, the University of Muenster, and West Virginia University have demonstrated control of magnetic thermal fluctuations using current. ...

Recommended for you

New blow for 'supersymmetry' physics theory

July 27, 2015

In a new blow for the futuristic "supersymmetry" theory of the universe's basic anatomy, experts reported fresh evidence Monday of subatomic activity consistent with the mainstream Standard Model of particle physics.

Rogue wave theory to save ships

July 29, 2015

Physicists have found an explanation for rogue waves in the ocean and hope their theory will lead to devices to warn ships and save lives.

Researchers build bacteria's photosynthetic engine

July 29, 2015

Nearly all life on Earth depends on photosynthesis, the conversion of light energy into chemical energy. Oxygen-producing plants and cyanobacteria perfected this process 2.7 billion years ago. But the first photosynthetic ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.