Tag: XMCD

Benedetta Casu’s #My1stLight

Benedetta Casu’s #My1stLight

Synchrotron: Destiny


When I was a physics student, the Physics Department of my University in the capital city of Sardinia organized a journey to Berlin for the senior master students to visit the most important labs. Among them, there was BESSY I. What an incredible experience, everything looked so fantastic, exciting, and complicated.


After that, for sake of curiosity, I attended the Italian synchrotron School that at the time was organized in Sardinia. I attended the school because I wanted to know more about synchrotron light, but I was sure that it would stay a “cultural opportunity” and nothing more.


A few years later I was offered a Ph.D. position at the University of Potsdam. The plan was that I would have been in charge of photocurrent investigations. BUT, the Ph.D. student that was in charge of the beamtime at Synchrotron in the same research group was never back from his vacation preferring to stay in sunny Spain. My supervisor decided that I would take over the Synchrotron beamtimes.


My very first beamtime was with the last photon at BESSY I.

Since then, I had the opportunity to perform wonderful experiments using Synchrotron facilities all over Europe, from working with the world record laterally resolved PEEM-LEEM at BESSY II to measuring XMCD at 150 mK at Petra III. I am also one of the German national delegates of the European Synchrotron and FEL User Organisation (ESUO).


Synchrotron was certainly my destiny

Image: Benedetta Casu during beamtime at BESSY II

Credit: Benedetta Casu

Observation of Magnetoelectric Coupling

Observation of Magnetoelectric Coupling

Multiferroic materials with coexisting ferroelectric and ferromagnetic orders have attracted much attention due to the magnetoelectric (ME) coupling opening prospects for alternative multifunctional electronic devices.  Switching magnetization by applied electric rather than magnetic field or spin-polarized current requires much less energy, making multiferroics promising for memory and logic applications. Due to a limited number of single-phase multiferroic compounds operating at room temperature, composite multiferroics containing ferroelectric and ferromagnetic components have been considered as viable alternatives. Moreover, it was shown that composite multiferroic materials often have much larger magnetoelectric coupling effect compared to their single-phase counterparts.

The recently emerged class of polycrystalline doped HfO2-based ferroelectric thin films, which are compatible with the modern Si technology, is a promising ferroelectric component in composite multiferroic heterostructures and it is therefore crucial to explore the ME effect at the ferroelectric/ferromagnetic interface in the heterostructures comprising doped HfO2. In this respect, a strong charge-mediated magnetoelectric coupling at the interface between classical ferromagnetic metal – Ni and ferroelectric HfO2has been recently predicted by theoretical modelling.

Read more on the Elettra Website

Image: Schematic drawing of a single capacitor device structure used in operando XAS/XMCD and HAXPES/MCDAD measurements with EELS (Electron energy loss spectroscopy) map of Co, Ni and O. Polarization vs. voltage hysteresis loop at RT and LT (left) and  MOKE (right) of Au/Co/Ni/HZO/W sample are also shown in figure.

Credit: Elettra

Disorder brings out quantum physical talents

Disorder brings out quantum physical talents

Quantum effects are most noticeable at extremely low temperatures, which limits their usefulness for technical applications. Thin films of MnSb2Te4, however, show new talents due to a small excess of manganese. Apparently, the resulting disorder provides spectacular properties: The material proves to be a topological insulator and is ferromagnetic up to comparatively high temperatures of 50 Kelvin, measurements at BESSY II show.  This makes this class of material suitable for quantum bits, but also for spintronics in general or applications in high-precision metrology.

Quantum effects such as the anomalous quantum Hall effect enable sensors of highest sensitivity, are the basis for spintronic components in future information technologies and also for qubits in quantum computers of the future. However, as a rule, the quantum effects relevant for this only show up clearly enough to make use of them at very low temperatures near absolute zero and in special material systems.

Read more on the HZB website

Image: The Dirac cone is typical for topological insulators and is practically unchanged on all 6 images (ARPES measurements at BESSY II). The blue arrow additionally shows the valence electrons in the volume. The synchrotron light probes both and can thus distinguish the Dirac cone at the surface (electrically conducting) from the three-dimensional volume (insulating).

Credit: © HZB

Comprehensive study of strontium hexaferrite platelets

Comprehensive study of strontium hexaferrite platelets

Researchers have synthesized and studied by a combination of soft X-ray techniques platelets of strontium hexaferrite allowing them to establish the differences and similarities between their synthesized nanostructures and commercial powders.

Most of the experiments have been performed within a collaboration among three beamlines of the ALBA Synchrotron.
Ferrites are ceramic materials usually made of large proportions of iron oxide (Fe2O3, rust) blended with small proportions of other metallic elements. These materials do not conduct electricity because they are insulators; and they are ferromagnetic, which means they can easily be magnetized or attracted to a magnet.

Strontium ferrites (SFO, SrFe12O19) in particular have a large magnetocrystalline anisotropy that gives it a high coercitivity, meaning that it is difficult to demagnetize. Since its discovery in the mid-20th century, this hexagonal ferrite has become an increasingly important material both commercially and technologically, finding a variety of uses and applications because of its low cost and toxicity. SFO has been used for permanent magnets, recording media, in telecommunications, and as a component in microwave, high-frequency and magneto-optical devices. Also, because they can be powdered and formed easily, they are finding their applications into micro and nano-types systems such as biomarkers, bio diagnostics and biosensors.

>Read more on the ALBA website

Magnetization ratchet in cylindrical nanowires

Magnetization ratchet in cylindrical nanowires

A team of researchers from Materials Science Institute of Madrid (CSIC), University of Barcelona and ALBA Synchrotron reported on magnetization ratchet effect observed for the first time in cylindrical magnetic nanowires (magnetic cylinders with diameters of 120nm and lengths of over 20µm).

These nanowires are considered as building blocks for future 3D (vertical) electronic and information storage devices as well as for applications in biological sensing and medicine. The experiments have been carried out at the CIRCE beamline of the ALBA Synchrotron. The results are published in ACS Nano.

The magnetic ratchet effect, which represents a linear or rotary motion of domain walls in only one direction preventing it in the opposite one, originates in the asymmetric energy barrier or pinning sites. Up to now it has been achieved only in limited number of lithographically engineered planar nanostructures. The aim of the experiment was to design and prove the one-directional propagation of magnetic domain walls in cylindrical nanowires.

>Read more on the ALBA website

Image: (extract) Unidirectional propagation of magnetization as seen in micromagnetic simulations and XMCD-PEEM experiments. See entire image here.