Tuning the magnetic anisotropy of lanthanides

The magnetism of lanthanide-directed nanoarchitectures on surfaces can be drastically affected by small structural changes. The study carried out in a collaboration between researchers from IMDEA Nanociencia and BOREAS beamline at ALBA reports the effect of the coordination environment in the reorientation of the magnetic easy axis of dysprosium-directed metal-organic networks on Cu(111). The authors show that the magnetic anisotropy of lanthanide elements on surfaces can be tailored by specific coordinative metal-organic protocols.

Recent findings have highlighted the potential of lanthanides in single atom magnetism. The stabilization of single atom magnets represents the ultimate limit on the reduction of storage devices. However, single standing atoms adsorbed on surfaces are not suitable for practical applications due to their high diffusion, i.e., low thermal stability. The next step towards more realistic systems is the coordination of these atoms in metal-organic networks.In 4f elements, the spin-orbit coupling (SOC) is larger than the crystal field, which might result in higher anisotropies. Furthermore, the crystal field acts as a perturbation of the SOC and can be tailored to increase the anisotropy by choosing an appropriate coordination environment. The strong localization of the 4f states reduces the hybridization with the surface, increasing the spin lifetimes, which is crucial, since a long magnetic relaxation time is mandatory for technological applications.

Read more on the ALBA website

Image: Cover picture showing the structure of the Dy-TPA network where C, H, O and Dy atoms are represented by black, red and green balls, respectively, the tilted orientation of the magnetic easy axis is represented by green arrows. 

Credit: ALBA

A new way of controlling skyrmions motion

A group of researchers from France has been able to create and guide skyrmions in magnetic tracks. These nanoscale magnetic textures are promising information carriers with great potential in future data storage and processing devices. Experiments at the CIRCE-PEEM beamline of the ALBA Synchrotron enabled to image how skyrmions move along tracks written with helium ions.

Magnetic skyrmions are local twists of the magnetization, considered as units (bits) in new magnetic data storage devices. They were named after British physicist Tony Hilton Royle Skyrme, who described these whirling configurations in the 80’s. But it was not until 2006 that there was evidence of their existence.

Skyrmions are of great interest for the scientific and industrial community as they could help finding more efficient ways to store and process information in our computers. They can be manipulated with lower electrical currents, opening a path for being used as information carriers.

But skyrmions are difficult to control. They do not move in straight lines when current is injected but naturally drift sideways, “killing” themselves. This is known as the Skyrmion Hall effect. In order to be used in devices, they need to be moved and controlled in a reliable way.

A group of researchers led by Olivier Boulle from SPINTEC (Grenoble, France) has a wide experience on the subject. They already reported in 2016 the first observation of magnetic skyrmions under conditions appropriate to the industrial needs, with experiments done at the ALBA Synchrotron.

Now, they have found a way to create and guide skyrmions in racetracks: by irradiating magnetic ultrathin layers with helium ions. This method enables to locally tune the magnetic properties to the desired point without introducing defects in the layer.

The samples were prepared and its magnetic properties were locally modified by helium ions irradiation to create the tracks. Later, they were characterized with different techniques to ensure the preparation was consistent. At the CIRCE beamline of the ALBA Synchrotron, using the PEEM photoemission electron microscope, they were able to image how skyrmions move along the tracks when receiving current pulses. Results were confirmed with magnetic force microscopy and micromagnetic simulations.

Read more on the ALBA website

Image: Micromagnetic simulation showing skyrmion motion along the irradiated racetrack. The irradiated racetrack confines the skyrmions within and they move with nanosecond (ns) current pulses along the track edge without being annihilated, thereby deminishing the Skyrmion Hall Effect (SkHE) (current densities in the parentheses are in A.m-2).

Controlling tiny magnetic swirls

Research on skyrmions may lead to more effective data storage

Skyrmions, commonly imagined as tiny magnetic swirls, are nanoscale magnetic quasi-particles that have recently become a hot topic because of their potential in the development of faster and more effective data storage devices.

For the first time, an international group of scientists, with lead scientists from the Massachusetts Institute of Technology, US, and the Max-Born-Institut in Berlin  have successfully been able to observe the formation of skyrmions in a magnetic material by using ultrashort laser pulses in a magnetic material, shedding light into the microscopic process and its time period. The X-ray pulses of the European XFEL’s revealed the creation of tiny skyrmion structures on nanometer length scales at a speed which is faster than previously thought possible. The results have been published in Nature Materials.

At the atomic level, magnetic materials resemble a sea of magnetic spins in either an ‘up’ or ‘down’ orientation. These spins are linked to each other so that a single spin change will affect the orientation of other spins. Skyrmions are tiny swirl-like structures where the center spin is oppositely aligned to the spins located at its boundary with a twisted spin configuration in between. These complex spin structures are very stable and small, making them interesting candidates for future spintronic devices. Spintronics exploits both the spin and the charge of electrons that could lower energy consumption in future memory devices and data storages.

Read more on the European XFEL website

Image: A laser pulse transforms a uniform magnetization (magnetization down everywhere) to a skyrmion swirl where the magnetization in the center points up. This transformation changes the so-called topology of the system.

Credit: B. Pfau, Max Born Institute