Ultrafast magnetism: heating magnets, freezing time

Magnetic solids can be demagnetized quickly with a short laser pulse, and there are already so-called HAMR (Heat Assisted Magnetic Recording) memories on the market that function according to this principle. However, the microscopic mechanisms of ultrafast demagnetization remain unclear. Now, a team at HZB has developed a new method at BESSY II to quantify one of these mechanisms and applied it to the rare-earth element Gadolinium, whose magnetic properties are caused by electrons on both the 4f and the 5d shells. This study is completing a series of experiments done by the team on Nickel, Iron-Nickel Alloys. Understanding these mechanisms is useful for developing ultrafast data storage devices.

New materials should make information processing more efficient, for example, through ultrafast spintronic devices that store data with less energy input. But to date, the microscopic mechanisms of ultrafast demagnetization are not fully understood. Typically, the process of demagnetization is studied by sending an ultrashort laser pulse to the sample, thereby heating it up, and then analyzing how the system evolves in the first picoseconds afterward.

Read more on the HZB website.

Image: The picture shows the glowing filament which keeps the sample at constant temperatures during the measurements.

Credit: © HZB

Understanding the physics in new metals

Researchers from the Paul Scherrer Institute PSI and the Brookhaven National Laboratory (BNL), working in an international team, have developed a new method for complex X-ray studies that will aid in better understanding so-called correlated metals. These materials could prove useful for practical applications in areas such as superconductivity, data processing, and quantum computers. Today the researchers present their work in the journal Physical Review X.

In substances such as silicon or aluminium, the mutual repulsion of electrons hardly affects the material properties. Not so with so-called correlated materials, in which the electrons interact strongly with one another. The movement of one electron in a correlated material leads to a complex and coordinated reaction of the other electrons. It is precisely such coupled processes that make these correlated materials so promising for practical applications, and at the same time so complicated to understand.

Strongly correlated materials are candidates for novel high-temperature superconductors, which can conduct electricity without loss and which are used in medicine, for example, in magnetic resonance imaging. They also could be used to build electronic components, or even quantum computers, with which data can be more efficiently processed and stored.

Read more on the BNL website

Image: Brookhaven Lab Scientist Jonathan Pelliciari now works as a beamline scientist at the National Synchrotron Light Source II (NSLS-II), where he continues to use inelastic resonant x-ray scattering to study quantum materials such as correlated metals.

Credit: Jonathan Pelliciari/BNL

An efficient tool to link X-ray experiments and ab initio theory

The electronic structure of complex molecules and their chemical reactivity can be assessed by the method of resonant inelastic X-ray scattering (RIXS) at BESSY II. However, the evaluation of RIXS data has so far required very long computing times. A team at BESSY II has now developed a new simulation method that greatly accelerates this evaluation. The results can even be calculated during the experiment. Guest users could use the procedure like a black box.

Molecules consisting of many atoms are complex structures. The outer electrons are distributed among the different orbitals, and their shape and occupation determine the chemical behaviour and reactivity of the molecule. The configuration of these orbitals can be analysed experimentally. Synchrotron sources such as BESSY II provide a method for this purpose: Resonant inelastic X-ray scattering (RIXS). However, to obtain information about the orbitals from experimental data, quantum chemical simulations are necessary. Typical computing times for larger molecules take weeks, even on high-performance computers.

Read more on the HZB website

Image: The electronic structure of complex molecules can be assessed by the method of resonant inelastic X-ray scattering (RIXS) at BESSY II

Credit: © Martin Künsting /HZB

Scientists streamline process for controlling spin dynamics

Marking a major achievement in the field of spintronics, researchers at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Yale University have demonstrated the ability to control spin dynamics in magnetic materials by altering their thickness. The study, published on the 18th January in Nature Materials, could lead to smaller, more energy-efficient electronic devices.

“Instead of searching for different materials that share the right frequencies, we can now alter the thickness of a single material—iron, in this case—to find a magnetic medium that will enable the transfer of information across a device,” said Brookhaven physicist and principal investigator Valentina Bisogni.

Read more on the BNL website

Image: An artist’s interpretation of measuring the evolution of material properties as a function of thickness using resonant inelastic x-ray scattering.