PEEM – Lightsources.org

A magnetic nano-elevator for spintronic devices

2022/05/272022/06/01

Researchers propose and demonstrate for the first time a new concept for the transfer of magnetic data in three dimensions based on geometrical effects for the interconnection of functional spintronic planes. The device is based on a magnetic nanostructure and promotes the spontaneous motion of bits without the need to apply any external stimuli. This work has promising applications in spintronics. Experiments at the CIRCE beamline in ALBA were key to characterize the magnetic structures and confirm their functioning.

Information technologies will be responsible for about 20% of electricity consumption worldwide by 2025, which urgently requires the development of new types of greener nanoelectronic devices. Spintronics, making use of not only the charge of electrons but also of its intrinsic angular momentum (its spin) is an emerging technology that can overcome some of these challenges, thanks to its non-volatility character, full compatibility with CMOS (complementary metal-oxide-semiconductor), low and fast write/reading processes, and high endurance.

However, as nanoelectronic devices move towards denser forms exploiting three dimensions, new mechanisms to efficiently interconnect functional planes become necessary. The shift to 3D devices should enable ultra-highly dense storage and memory devices, but their realization brings huge challenges, from their fabrication to their interconnection or effective heat dissipation.

Read more on the ALBA website

Image: PEEM magnetic nano-elevator

A new way of controlling skyrmions motion

2021/07/152021/07/19

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).

Artificial spin ice toggles twist in X-ray beams on demand

2021/05/242021/05/28

SCIENTIFIC ACHIEVEMENT

Advanced Light Source (ALS) studies helped scientists understand how a nanoscale magnetic lattice (an artifical spin ice) acts as a toggle switch for x-ray beams with spiral character.

SIGNIFICANCE AND IMPACT

The findings represent an important step toward the development of a versatile new tool for probing or controlling exotic phenomena in electronic and magnetic systems.

A curious singularity

Artificial spin ices (ASIs) are engineered arrays of nanomagnets that are often “frustrated,” meaning that the magnets, constrained by geometry, cannot align themselves to minimize their interaction energy. Water ice exhibits a similar property with regard to the positioning of hydrogen atoms.

While studying ASIs, a collaboration between scientists from the University of Kentucky and the ALS (see related feature article) made an interesting observation: light scattered from certain ASIs produced diffraction patterns in which spots of constructive interference were shaped like donuts instead of dots. The donuts were indicative of a phase singularity—a hallmark of light with a property known as orbital angular momentum (OAM).

Read more on the ALS website

Image: When x-rays are scattered from a patterned array of nanoscale magnets with a lattice defect, the beams acquire a spiral character (orbital angular momentum, or OAM) that produces diffraction patterns with donut-shaped spots. Researchers have found that these OAM beams can be switched on and off by adjusting the temperature or applying an external magnetic field.

Unexpected rise in ferroelectricity as material thins

2020/06/182020/07/02

SCIENTIFIC ACHIEVEMENT

Researchers working at the Advanced Light Source (ALS) showed that hafnium oxide surprisingly exhibits enhanced ferroelectricity (reversible electric polarization) as it gets thinner.

SIGNIFICANCE AND IMPACT

The work shifts the focus of ferroelectric studies from more complex, problematic compounds to a simpler class of materials and opens the door to novel ultrasmall, energy-efficient electronics.

Ferroelectric lower limit?

Distortions in the atomic geometries of certain materials can lead to ferroelectricity—the presence of electric dipoles (charge separations) with switchable polarizations. The ability to control this polarization with an external voltage offers great promise for ultralow-power microprocessors and nonvolatile memory.

As electronic devices become smaller, however, the materials used to store and manipulate electronic data are being pushed to low-dimensional extremes. Properties that function reliably in bulk materials often diminish in ultrathin films just a few atomic units thick. Therefore, exploring the critical thickness limit in “polar” materials (i.e., materials having spontaneous electric polarization) is not only a fundamental issue for nanoscale ferroelectric research, it also has extensive implications for the future of high-density ferroelectric-based electronics.

Read more on Advanced Light Source (ALS) website

Image : A thin layer of hafnium oxide (two unit-cell thicknesses, or about 1 nm) has an electric polarization that’s reversible by an external electric field, making it attractive for use in next-generation low-power microelectronics.

Credit: Ella Maru Studio

Comprehensive study of strontium hexaferrite platelets

2020/01/082020/01/28

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

Electronics of future: magnetic properties of InSb-Mn

2019/12/062019/12/10

The recent volume of “ACS Nano Letters” presented the results of research conducted at the SOLARIS National Synchrotron Radiation Centre and at the Academic Centre for Materials and Nanotechnology of the University of Science and Technology in Kraków.

The research was led by Dr Katarzyna Hnida-Gut and demonstrated that the magnetic properties of indium antimonide nanowires with an addition of manganese (InSb-Mn) can be controlled by the concentration of the dopants. The ground-breaking aspect of this research was that for the first time in the pulse electrosynthesis process in AAO pores (anodic aluminium oxide) high quality InSb-Mn nanowires were obtained, making use of previously determined optimum conditions for the synthesis of the semiconductor indium antimonide.

Some of the measurements conducted as part of the research project were performed using synchrotron radiation at the SOLARIS Centre in Kraków. Thanks to an experiment conducted on PEEM/XAS beamline, it was possible to determine the local structure in the vicinity of manganese atoms. This allowed for the confirmation of the hypothesis that “the manganese atoms in the studied nanowires form small clusters, such as Mn3. It is precisely these clusters that are the source of the magnetic response at room temperature,” explains Dr. Marcin Sikora, one of the co-authors of the paper.

>Read more on the SOLARIS website

In-gap states and band-like transport in memristive devices

2019/03/222019/03/27

The creation of point defects in matter can profoundly affect the physical and chemical properties of materials. If appropriately controlled, these modifications can be exploited in applications promising advanced and novel functionalities. Redox-based memristive devices – one of the most attractive emerging memory technologies – provide one of the most striking examples for the potential exploitation of defects. Applying an external electric field to an initially insulating oxide layer is known to induce a non-volatile, voltage-history dependent switching between a low resistance state and a high resistance state, also named memristive device. This switching occurs through the creation and annihilation of the so-called conductive filaments, which are generated at the nanoscale by assembly of donor-type point defects such as oxygen vacancies.
To date, the exact relationship between concentration and nanoscale distribution of defects within the filament on the one hand and the electronic transport properties of the devices on the other hand is still elusive. Due to limitations in sensitivity or spatial resolution of most characterization methods, the electronic structure of conductive filaments has not yet been characterized in detail. However, this knowledge is crucially needed as input for the development of electronic transport models with high predictive power.

>Read more on the Elettra website

Image: (a) Ti³⁺ map based on the Ti 3p_3/2 spectrum. (b) Ti 2p _3/2 spectra for the filament and the surrounding. (c) Spatial map of the in-gap state distribution. (d) Valence band spectrum extracted from the filament at a photon energy of 463.3 eV with a fit of the valence band maximum and the in-gap states (red lines). (e) Band diagram of the device calculated based on the position of the in-gap states. The blue line shows the conduction band and the dashed green lines shows position of the defect states obtained by PEEM in respect to the conduction band

Tunable ferromagnetism in a 2D material at room temperature

2018/12/052018/12/06

Breakthroughs in next-generation spintronic logic and memory devices could hinge on our ability to control spin behavior in two-dimensional materials—stacks of ultrathin layers held together by relatively weak electrostatic (van der Waals) forces. The reduced dimensionality of these so-called “van der Waals materials” often leads to tunable electronic and magnetic properties, including intrinsic ferromagnetism. However, it remains a challenge to tune this ferromagnetism (e.g. spin orientation, magnetic domain phase, and magnetic long-range order) at ambient temperatures.

In this work, researchers performed a study of Fe₃GeTe₂, a van der Waals material that consists of Fe₃Ge layers alternating with two Te layers. The material’s magnetic properties were characterized using a variety of techniques, including x-ray absorption spectroscopy (XAS) with x-ray magnetic circular dichroism (XMCD) contrast at Beamline 6.3.1 and photoemission electron microscopy (PEEM) at Beamline 11.0.1.

Image: PEEM images for unpatterned and patterned Fe₃GeTe₂ samples at 110 K and 300 K. The unpatterned samples formed stripe domains at 110 K, which disappeared at 300 K. The patterned samples formed out-of-plane stripe domains at 110 K and transitioned to in-plane vortex states at 300 K, demonstrating control over magnetism at room temperature and beyond.

Magnetization ratchet in cylindrical nanowires

2018/06/262018/07/11

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.

Subfilamentary Networks in Memristive Devices

2017/12/112018/01/17

Redox-based memristive devices are one of the most attractive emerging memory technologies.

…in terms of scaling, power consumption and speed. In these devices, external electrical stimuli cause changes of the resistance of an oxide layer sandwiched between two metal electrodes. In the simplest application, the device can be set into a low resistance state (LRS) and reset into a high resistance state (HRS), which may encode a logical one and zero, respectively. The major obstacle delaying large-scale application, however, is the large cycle-to-cycle (C2C) and device-to-device (D2D) variability of both LRS and HRS resistance values. These variabilities describe the stochastic nature of the switching process within one cell, resulting in different resistances obtained for each switching cycle and different resistances obtained for different cells on the same chip.