Enhanced magnetic hybridization of a spinterface

Interfaces between organic semiconductors and ferromagnetic metals offer intriguing opportunities in the rapidly developing field of organic spintronics. Understanding and controlling the spin-polarized electronic states at the interface is the key toward a reliable exploitation of this kind of systems. It is indeed important to master and reliably reproduce the chemical reactions responsible of the spin-polarization at the interface.

Here we propose an approach consisting in the insertion of an ultrathin, two-dimensional Cr4O5 magnetic oxide layer at the interface between a C60 fullerene organic semiconductor and a Fe(001) ferromagnetic metal to both maximize the spin polarization and to overcome the reproducibility issues usually present in case of direct interface between metallic layer and organic semiconductor.
C60 fullerene showed a greater surface diffusivity when growing on Cr4O5 compared to the Fe(001) case. From the first stages of surface coverage, C60 tends to form islands rather than isolated molecules, leading to a well-ordered growth at higher thicknesses (Figure 1, above).

>Read more on the Elettra website

Figure 1STM image 200 x 200 nm2 of the surface of a C60/ Cr4O5/Fe(001) sample with a fullerene coverage of about 0.5 ML. The image was taken at room temperature with ΔV= 1.7 V, I = 400 pA.

“X-ray streaking” allows ultrafast processes to be followed using a single pulse of light

Grazing light for rapid events

An international team of scientists has developed a new experimental method at the FLASH X-ray laser which allows the sequence of events involved in a process to be observed using a single, ultrashort pulse of light from FLASH. Their method is called “X-ray streaking” and enables researchers to observe ultrafast processes continuously, instead of being confined to taking snapshots at discrete intervals using separate X-ray pulses. Apart from the extreme brightness of the FLASH beam, the scientists also made use of an X-ray lens which they introduced into the beamline in a particular configuration, so as to capture a chronological sequence of events using a single X-ray pulse. To demonstrate the functionality of X-ray streaking, they observed the ultrafast demagnetisation of cobalt.

The invention of X-ray lasers has considerably boosted the study of the dynamics of matter. Pump-probe experiments allow artificially induced (“pumped”) processes and reactions to be photographed (“probed”) using an extremely short X-ray pulse at predetermined intervals. Ideally, these photographs, taken with different time delays, can then be assembled to create a film showing the sequence of events during an ultrafast process with a temporal resolution of the order of femtoseconds. One limitation of this otherwise promising experimental technique is, however, that the experiment has to be conducted all over again for each time delay. This means that before each observation, the process of interest must be triggered using the same starting conditions and it must run through the same sequence of events – both of which rule out extreme experimental conditions.

>Read more on the FLASH website

Image Caption: (a,b) Raw images from the reflection and reference detectors respectively. Both the images for the pumped and the un-pumped event are acquired using a single x-ray pulse. (c) Transient reflectivity image (as defined in the text) calculated from the images shown in (a,b). (d) Reshaped transient reflectivity image after calibration of the time window. Article published in Scientific Reports.

 

Topological insulator gap in graphene contacted with Pb

Up to now the proposed modifications do not allow to introduce graphene to existing electronic devices.

Graphene is the most promising two dimensional material for nanoelectronic applications featuring the relativistic-like electronic spectrum. Contact of graphene with various materials and its functionalization allows to manipulate the electronic structure, e.g. to change the conductivity type and band gap creation. The latter is of great interest due to the requirements for graphene transistor realisation. Furthermore, graphene contact with heavy/magnetic metals results in the lifting of the spin degeneracy of the Dirac cone, opening the spintronics field for its applications. However, up to now the proposed modifications do not allow to introduce graphene to existing electronic devices.

>Read more on the Elettra website.

Image: a) Sketch of the studied system, the Pb atoms presented by yellow spheres; b) ARPES image of graphene/Pb/Pt(111) in the region of K point, taken as a sum of two spectra with p-and s-polarization of light; c) schematic spin structure of the graphene states in the case of large “intrinsic” spin-orbit interaction d) ARPES mapping of the system in two orthogonal k-directions near the K point of graphene.

Electrical hiding of magnetic information

Results have been published in Sientific Reports.

Researchers have proved the ability of peculiar magnetic materials to hide magnetic information and reveal it under certain conditions and at room temperature.

Since the 1950’s, magnetic materials have been used to store all kinds of information. Magnetically stored information is convenient because it is easily accessible using very well-known magnetic data reading procedures. However, sensitive information must be carefully stored to ensure confidentiality; thus easy access becomes a bad instead of a good feature. The optimal way to prevent unauthorised information access is to make it invisible.

>Read more on the ALBA website

Antiferromagnetic dysprosium reveals magnetic switching with less energy

HZB scientists have identified a mechanism with which it may be possible to develop a form of magnetic storage that is faster and more energy-efficient.

They compared how different forms of magnetic ordering in the rare-earth metal named dysprosium react to a short laser pulse. They discovered that the magnetic orientation can be altered much faster and with considerably less energy if the magnetic moments of the individual atoms do not all point in the same direction (ferromagnetism), but instead point are rotated against each other (anti-ferromagnetism). The study was published in Physical Review letters on 6. November 2017 and on the cover of the print edition.

Dysprosium is not only the atomic element with the strongest magnetic moments, but it also possesses another interesting property: its magnetic moments point either all the same direction (ferromagnetism) or are tilted against each other, depending on the temperature. This makes it possible to investigate in the very same sample how differently oriented magnetic moments behave when they are excited by an external energy pulse.

>Read More on the Bessy II (HZB) website

Image: A short laser pulse pertubates magnetic order in dysprosium. This happens much faster if the sample had a antiferromagnetic order (left) compared to ferromagnetic order (right). Credit: HZB

Magnetic structures take a new turn

The unexpected finding that in an ‘artificial spin ice’ magnetostatic energy can be transformed into directed rotation of magnetization provides fresh insights into such nano-patterned magnetic structures — and might enable novel applications in nanoscale devices.

Magnetism and rotation are intimately related. This connection can lead to surprising and non-intuitive effects, as first demonstrated a century ago, when it was predicted, and observed, that changing the magnetization in a piece of ferromagnetic material (such as iron) rotates it, ever so slightly; conversely, spinning a non-magnetised piece of the same material magnetizes it. These phenomena are known as Einstein—de Haas and Barnett effects, respectively, and are beautiful phenomena described in many physics textbooks. Now, Sebastian Gliga and colleagues in the Laboratory for Multiscale Materials Experiments at PSI, led by of Laura Heyderman, report in Nature Materials [1] the discovery of another sort of rotation in a magnetic structure, one that came as a surprise. They observed that after magnetising their sample, the magnetisation started to consistently rotate in one of two possible directions, without an obvious reason why one way should be preferred over the other.

Read more on the PSI website