Keywords: research reactor (90) spintronics (93)

Science Highlight    19.10.2017

High Field Magnet at BER II: Insight into a hidden order

Additional spots appear on the neutron detector starting at a magnetic field strength of 23 Tesla that reveal the new magnetic order in the crystal.


Copyright: HZB

A specific uranium compound has puzzled researchers for thirty years. Although the crystal structure is simple, no one understands exactly what is happening once it is cooled below a certain temperature. Apparently, a “hidden order” emerges,  whose nature is completely unknown.Now physicists have characterised this hidden order state more precisely and studied it on a microscopic scale. To accomplish this, they utilised the High-Field Magnet at the HZB that permits neutron experiments to be conducted under conditions of extremely high magnetic fields.

Crystals comprising the elements uranium, ruthenium, rhodium, and silicon have a simple geometric structure and should no longer be hiding any secrets. However, that is not the case – quite the contrary. At temperatures below 17.5 Kelvin, a new internal order emerges: Something in the material orders in some yet undisclosed way, releasing a certain amount of heat as a signature. Known is only that the order is not due to static magnetic moments. More than 1000 publications have already appeared on this topic without having lifted the veil.

Perfect crystals at low temperatures

However, conventional magnetic states can be induced in various ways such as doping, pressure or by large magnetic fields. This may help to shed more light on the hidden order itself. In order to study at least new magnetic states emerging from the hidden order, physicists from the HZB, from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Amsterdam, and Leiden University, Netherlands, have investigated flawless crystals made of U(Ru0.92 Rh0.08)2Si2 at cryotemperatures and extremely high magnetic fields using neutrons.

New magnetic order above 21,6 Tesla

“The neutron scattering experiments conducted under extremely high magnetic fields have shown that at about 21.6 Tesla, there really is a new magnetic phase transition”, explains first author Dr. Karel Prokeš from the HZB. “This means that a new magnetic order has become established in the crystal.” This involves an uncompensated antiferromagnetic order in which the magnetic moments of the uranium atoms point alternatingly up-up-down in opposite directions.

Within minutes, the editors replied: yes, it should be published.

When Prokeš submitted the joint manuscript to the renowned journal Physical Review B, he received a positive reply within 19 minutes. The work was published as a “Rapid Communication” – a new speed record that says something about the importance of this experiment for solid-state physics.   

Published in Physical Review B (2017): Magnetic structure in a U(Ru0.92Rh0.08)2Si2 single crystal studied by neutron diffraction in static magnetic fields up to 24 T. K. Prokeš, M. Bartkowiak, O. Rivin, O. Prokhnenko, T. Förster, S. Gerischer, R. Wahle, Y.-K. Huang, and J. A. Mydosh

Doi: 10.1103/PhysRevB.96.121117

 

arö


           



You might also be interested in
  • <p>Experiments at the femtoslicing facility of BESSY II revealed the ultrafast angular momentum flow from Gd and Fe spins to the lattice via orbital moment during demagnetization of GdFe alloy.</p>SCIENCE HIGHLIGHT      10.05.2019

    Laser-driven Spin Dynamics in Ferrimagnets: How does the Angular Momentum flow?

    When exposed to intense laser pulses, the magnetization of a material can be manipulated very fast. Fundamentally, magnetization is connected to the angular momentum of the electrons in the material. A team of researchers led by scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now been able to follow the flow of angular momentum during ultrafast optical demagnetization in a ferrimagnetic iron-gadolinium alloy at the femtoslicing facility of BESSY II. Their results are helpful to understand the fundamental processes and their speed limits. The study is published in Physical Review Letters. [...]


  • <p>The cones represents the magnetization of the nanoparticles. In the absence of electric field (strain-free state) the size and separation between particles leads to a random orientation of their magnetization, known as superparamagnetism</p>SCIENCE HIGHLIGHT      14.02.2019

    Spintronics by “straintronics”: Superferromagnetism with electric-field induced strain

    Data storage in today’s magnetic media is very energy consuming. Combination of novel materials and the coupling between their properties could reduce the energy needed to control magnetic memories thus contributing to a smaller carbon footprint of the IT sector. Now an international team led by HZB has observed at the HZB lightsource BESSY II a new phenomenon in iron nanograins: whereas normally the magnetic moments of the iron grains are disordered with respect each other at room temperature, this can be changed by applying an electric field: This field induces locally a strain on the system leading to the formation of a so-called superferromagnetic ordered state. [...]


  • <p>Neutrons (red arrows) detect the presence of Lithium ions which have migrated into the silicon anode.</p>SCIENCE HIGHLIGHT      28.01.2019

    Batteries with silicon anodes: Neutron experiments show how formation of surface structures reduces amp-hour capacity

    In theory, silicon anodes could store ten times more lithium ions than graphite anodes, which have been used in commercial lithium batteries for many years. However, the amp-hour capacity of silicon anodes so far has been declining sharply with each additional charge-discharge cycle. Now an HZB team at BER II of the HZB in Berlin and the Institut Laue-Langevin in Grenoble has utilised neutron experiments to establish what happens at the surface of the silicon anode during charging and what processes reduce this capacity. [...]




Newsletter