Physicists observe magnetic 'devil's staircase'

June 24, 2015 by Lisa Zyga feature
Devil’s staircase behavior emerges in the magnetic structure of a cobalt oxide material. Three magnetic phases are shown here, where the arrows represent the different spin configurations that define each phase. These phases have nearly degenerate magnetic energies, so they all coexist as stable phases, but can be easily altered by external modifications such as doping. Credit: T. Matsuda, et al. ©2015 American Physical Society

(Phys.org)—Many hiking trails feature a "devil's staircase"—a set of steps that are often steep and difficult to climb. The devil's staircase is also the name of a mathematical function whose graph exhibits a jagged step-like organization reminiscent of a real staircase, although in a highly ordered fractal pattern. Devil's staircase behavior emerges in a variety of areas, such as in crystals, phase transitions, and statistical physics.

Now in a new paper published in Physical Review Letters, researchers led by Hiroki Wadati, an associate professor at the University of Tokyo, have observed devil's staircase behavior in a certain magnetic material: the SrCo6O11. By analyzing the of this material, the researchers found that it contains a large number of that have nearly "degenerate," or equal, magnetic energies. The coexistence of these many nearly degenerate magnetic structures gives rise to the devil's staircase behavior, which has the appearance of many (in principle, an infinite number of) proportional step-like structures.

Although the devil's staircase behavior emerges from microscopic effects, the behavior is also reflected in the material's macroscopic properties. One of the most intriguing properties is the material's giant magnetoresistance, which means that an applied magnetic field changes the material's electrical resistance. This property could have implications for designing artificial materials with novel functionalities.

To uncover these microscale magnetic properties of the cobalt oxide, the researchers used a technique called soft X-ray scattering (RSXS), which involves bombarding a material with X-rays and measuring the energy and momentum of the scattered X-rays. As a relatively recent development, RSXS has proven to be a powerful tool for investigating the ordered structures in solid materials. For one of the first times ever, the researchers here used RSXS with magnetic fields of several Tesla. The technique enabled the researchers to discover several microscale magnetic structures that escaped detection in earlier experiments.

The scientists attribute the material's unusually large number of nearly degenerate magnetic phases—and the resulting devil's staircase behavior—to competition between the magnetic phases. This competition results in magnetic frustration, as no single phase is strong enough to dominate the others. The results show that strong magnetic frustration is a key ingredient for giving the material its giant magnetoresistance and also makes the material highly sensitive to very low chemical doping.

To demonstrate this sensitivity, the researchers showed that substituting just 3% of the strontium atoms with barium atoms destroys almost all of the material's degenerate magnetic phases, which greatly changes its overall magnetic properties. Because the material's properties are easily tunable in this way, the scientists hope that this research may offer a path toward engineering and controlling the material's magnetic and electrical properties for various technological applications.

"In future resonant soft X-ray diffraction studies, one can expect to find similar devil's staircase behavior in other materials," Wadati told Phys.org. "The devil's staircase behavior may lead to the development of novel types of spintronics , which can use discrete levels of electrical resistivity."

Explore further: Anomalous spin ordering revealed by brilliant synchrotron soft X-rays

More information: T. Matsuda, et al. "Observation of a Devil's Staircase in the Novel Spin-Valve System SrCo6O11." Physical Review Letters. DOI: 10.1103/PhysRevLett.114.236403
Also at arXiv:1412.7945 [cond-mat.str-el]

Related Stories

Giant magnetic effects induced in hybrid materials

April 21, 2015

Proximity effects in hybrid heterostructures, which contain distinct layers of different materials, allow one material species to reveal and/or control properties of a dissimilar species. Specifically, for a magnetic thin ...

New discovery could pave the way for spin-based computing

September 25, 2014

Electricity and magnetism rule our digital world. Semiconductors process electrical information, while magnetic materials enable long-term data storage. A University of Pittsburgh research team has discovered a way to fuse ...

Recommended for you

Single-photon detector can count to four

December 15, 2017

Engineers have shown that a widely used method of detecting single photons can also count the presence of at least four photons at a time. The researchers say this discovery will unlock new capabilities in physics labs working ...

Real-time observation of collective quantum modes

December 15, 2017

A cylindrical rod is rotationally symmetric - after any arbitrary rotation around its axis it always looks the same. If an increasingly large force is applied to it in the longitudinal direction, however, it will eventually ...

A shoe-box-sized chemical detector

December 15, 2017

A chemical sensor prototype developed at the University of Michigan will be able to detect "single-fingerprint quantities" of substances from a distance of more than 100 feet away, and its developers are working to shrink ...

An ultradilute quantum liquid made from ultra-cold atoms

December 14, 2017

ICFO researchers created a novel type of liquid 100 million times more dilute than water and 1 million times thinner than air. The experiments, published in Science, exploit a fascinating quantum effect to produce droplets ...

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.