Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How magnetic fields can fix crystal twinning

31.01.2018

Special coupling of magnetic moments in high-temperature superconductors allows to reorient crystalline domains leading to “perfect” single crystals.

In many cases, it is important to be able to take measurements along different directions in the crystal lattice in order to study the physical properties of new materials, such as high-temperature superconductors. However, this requires single crystals without so-called twin domains, i.e., without any internal twists.


Graphical representation of the magnetic interactions relevant to magnetic detwinning in EuFe₂As₂. Essential is the bi-quadratic coupling between Fe and Eu indicated by blue-red arrows.

© Universität Augsburg/IfP/EKM

Iron pnictide superconductors, which are currently being studied intensively, show twin domains, which until now could only be avoided by application of high pressure. This is technically challenging to implement and limits the possibilities of investigation. Recently, a major breakthrough has been achieved: in iron pnictide superconductors with large europium moments, twin domains can be reoriented by small magnetic fields to achieve a mono-domain and fully detwinned single crystal.

This surprising and novel effect is based, as has now been elucidated by physicists at the University of Augsburg and the Naval Research Laboratory in Washington (USA), on a special magnetic interaction between the magnetic moments of europium and iron.

Most parent compounds of modern high-temperature superconductors, the so-called iron pnictides, feature a phase transition in which the crystal structure distorts within the tetragonal ab-plane. This distortion leads to the formation of micrometer-sized twin domains, which obscure the in-plane anisotropies of important physical properties.

Three years ago, physicists from the Universities of Augsburg, Göttingen, Stuttgart, and San Diego discovered a remarkable effect in EuFe₂As₂. The application of small magnetic fields leads to a reorientation of the twin domain walls at low temperatures, leaving the crystal fully detwinned. It is even possible to switch back and forth between different crystal orientations several times by further increasing the magnetic field.

This effect allows for a better investigation of the directional dependence of the physical properties, which is considered crucial for the understanding of high-temperature superconductivity. However, a necessary and physically meaningful explanation of this effect was so far missing.

Two experimental physicists at the University of Augsburg in cooperation with a theoretical physicist from the US have now published a comprehensive quantitative description of this very unusual coupling between the crystal lattice and the applied magnetic field in the journal Physical Review X.

The compound EuFe₂As₂ has two types of magnetic moments, which originate from strongly localized 4f orbitals of the europium atoms as well as from predominantly delocalized 3d orbitals of the iron atoms. Since iron pnictides without europium moments show no comparable behavior, it is clear that the latter play an important role. Their coupling to the crystal lattice, however, is much too weak to explain the experimental observations.

The crucial point in the theoretical description was, therefore, the modeling of the interaction between the europium and iron moments. Due to the symmetrical arrangement of the moments in the crystal lattice, the typical, so-called linear Heisenberg coupling is ineligible.

By introducing a minuscule biquadratic coupling between the Eu and Fe magnetic moments, which tries to make the two as parallel as possible, all observations are quantitatively described. This is remarkable, as the interaction strength is several orders of magnitude smaller than typical electron and lattice energies.

In addition to the description of the previous experimental observations, the theory published in the journal Physical Review X also predicts further abrupt changes in the crystal orientation in EuFe₂As₂ for very high magnetic fields. First signs of this have already been observed. In general, field-induced detwinning enables a number of new investigation methods to study the directional-dependent properties of high-temperature superconductors. This opens up new possibilities to gain an improved understanding of these fascinating materials.


Publication:
Jannis Maiwald, I.I. Mazin, and Philipp Gegenwart, Microscopic Theory of Magnetic Detwinning in Iron-Based Superconductors with Large-Spin Rare Earths, Physical Review X, 8, 011011 (2018), http://doi.org/10.1103/PhysRevX.8.011011

Weitere Informationen:

http://doi.org/10.1103/PhysRevX.8.011011

Klaus P. Prem | idw - Informationsdienst Wissenschaft
Further information:
http://www.uni-augsburg.de/

More articles from Materials Sciences:

nachricht Graphene origami as a mechanically tunable plasmonic structure for infrared detection
25.04.2018 | University of Illinois College of Engineering

nachricht Scientists create innovative new 'green' concrete using graphene
24.04.2018 | University of Exeter

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Why we need erasable MRI scans

New technology could allow an MRI contrast agent to 'blink off,' helping doctors diagnose disease

Magnetic resonance imaging, or MRI, is a widely used medical tool for taking pictures of the insides of our body. One way to make MRI scans easier to read is...

Im Focus: BAM@Hannover Messe: innovative 3D printing method for space flight

At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.

Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

World's smallest optical implantable biodevice

26.04.2018 | Power and Electrical Engineering

Molecular evolution: How the building blocks of life may form in space

26.04.2018 | Life Sciences

First Li-Fi-product with technology from Fraunhofer HHI launched in Japan

26.04.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>