Researchers achieve greater precision in measuring the movement of microscopic magnets

Oct 26, 2012
Schematic illustration of a ferromagnetic Josephson junction used for detecting magnetic domain wall motion. A domain wall (pink) inside a ferromagnetic wire (FW) between two superconducting electrodes (S) is driven into oscillatory motion by a voltage (bottom) applied horizontally across the wire. The current and voltage vertically across the junction become a precise multiple of the domain wall oscillation frequency. Credit: 2012 American Institute of Physics

At microscopic scales, magnetic materials are full of structure. Tiny magnets, called domains, order themselves in ways that control the magnetic properties of the bulk material. Technologies such as hard disk drives exploit this order by storing information in individual domain directions. In the past decade, however, engineers and scientists have focused increasingly on what happens between—rather than within—domains. They have also proposed new logic, memory, sensing and communication devices that manipulate the walls separating neighboring domains. Now, Shin'ichi Hikino from the RIKEN Advanced Science Institute, along with three Japan-based colleagues, has proposed a new and highly sensitive experimental technique for measuring domain wall motion.

The researchers adapted the technology behind one of the most precise known measures of voltage. The approach uses two superconductors separated by a thin layer of non-superconducting material. When the thin junction, called a , is exposed to microwave radiation, the voltage across the junction becomes a precise multiple of the . In fact, this multiple can be defined entirely in terms of fundamental physical constants, leading to a measurement precision so high that it is used to define the value of a volt by standards institutes around the world.

Hikino and colleagues realized that, if the non-superconducting layer was made from a ferromagnet containing two or more , the motion of the domain walls could be measured with a similarly high precision. This is due to the fact that each moving wall has a magnetic moment, which affects the current and voltage across the junction. In their theoretically proposed experimental setup, a voltage applied to the ferromagnetic wire causes its domain walls to oscillate. Then, the measured current and voltage across the junction become a precise multiple of the walls' oscillation frequency, which plays the role of the frequency usually used.

As a result, the junction voltage can be used to measure the wall oscillation frequency with a precision six orders of magnitude better than conventional methods, which have errors of one part in a thousand or worse. The expected size of both the current and voltage across the junction are in the micro-ampere and micro-volt range for a ferromagnetic wire with a thickness of five nanometers. These quantities are easily measured, making the proposal experimentally feasible.

Hikino expects the technique to be applicable to uniform domain wall motion as well, and believes the approach could form the basis for a standard unit for magnetic dynamics, similar to the volt.

Explore further: Could 'Jedi Putter' be the force golfers need?

More information: Hikino, S., Mori, M., Koshibae, W. & Maekawa, S. Towards precise measurement of oscillatory domain wall by ferromagnetic Josephson junction. Applied Physics Letters 100, 152402 (2012). apl.aip.org/resource/1/applab/v100/i15/p152402_s1?isAuthorized=no

Related Stories

Road to AC voltage standard leads to important junction

Jul 20, 2006

After 10 years of research, the National Institute of Standards and Technology (NIST) has unveiled the world's first precision instrument for directly measuring alternating current (AC) voltages. The instrument is being tested ...

NIST ships first programmable AC/DC 10-volt standard

Oct 27, 2010

Extending its 26-year tradition of innovative quantum voltage standards, researchers at the National Institute of Standards and Technology (NIST) have begun shipping a new 10-volt standard to users around ...

Moving forward, spin goes sideways

Oct 07, 2011

Building electronic devices that work without needing to actually transport electrons is a goal of spintronics researchers, since this could lead to: reduced power consumption, lower levels of signal noise, faster ...

Recommended for you

Could 'Jedi Putter' be the force golfers need?

Apr 18, 2014

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...

Better thermal-imaging lens from waste sulfur

Apr 17, 2014

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Jeffhans1
1 / 5 (1) Oct 26, 2012
This makes me wish for a hard drive from 10 years from now.
ValeriaT
1 / 5 (1) Nov 04, 2012
It could find an application in racetrack memory

More news stories

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...