Tag: spintronic devices

Magneto-ionic control of artificial antiferromagnets

Magneto-ionic control of artificial antiferromagnets

An international research collaboration, led by the Universitat Autònoma de Barcelona, has demonstrated the potential of magneto-ionics – control of magnetism via voltage-driven ion migration – to modulate the properties of artificial antiferromagnets. The study opens new avenues for spintronic devices. Experiments done at the ALBA Synchrotron were crucial to shed light on the mechanisms responsible for the magneto-ionic control of Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.

Voltage-driven ion migration provides a powerful mechanism to modulate magnetism and spin-related phenomena in solids, offering significant potential for the development of energy-efficient next-generation micro- and nanoelectronic devices. Synthetic antiferromagnets, comprising two ferromagnetic layers antiferromagnetically coupled via a thin non-magnetic spacer, offer key advantages for spintronic applications, including enhanced thermal stability, reduced magnetostatic interactions, and robustness against external magnetic fields in magnetic tunnel junctions. Despite its technological promise, magneto-ionic control of antiferromagnetic coupling in multilayers remains largely unexplored and poorly understood, especially in systems that avoid reliance on platinum-group metals.

In a recent publication, scientists from the Universitat Autònoma de Barcelona (UAB), Singulus Technologies (Germany), the Catalan Institution for Research and Advanced Studies (ICREA)  and the ALBA Synchrotron have demonstrated room-temperature voltage control of Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in Cobalt/Nickel-based synthetic antiferromagnets.

The experiments reveal voltage-induced transitions between ferrimagnetic (uncompensated) and antiferromagnetic (fully compensated) states, along with notable modulation of the RKKY bias field offset, the emergence of additional switching events, and the formation of skyrmion-like domain bubbles under relatively low gating voltages.

These effects are attributed to voltage-driven oxygen migration within the multilayers, as confirmed by microscopic and spectroscopic analyses. X-ray absorption spectra (XAS) of the samples were performed at the BOREAS beamline of ALBA. XAS was used to characterize, at room temperature, the elemental composition and oxidation state of the films. The findings were crucial to understand the mechanisms of the magneto-ionic control of the synthetic antiferromagnet structures.

A new approach to optimize magnetic tunnel junctions

Magnetic tunnel junctions continue to face several key challenges that hinder their performance and scalability:

  • limited magnetic stability of the reference layer under external magnetic fields.
  • interlayer dipolar interactions, where the magnetic moment of the reference layer disturbs the magnetization reversal of the free layer, degrading device performance.
  • poor thermal stability across a wide temperature range.
  • restricted areal density, as scaling down the lateral dimensions of magnetic tunnel junctionsoften leads to superparamagnetic effects that compromise device reliability.

To address these limitations, synthetic antiferromagnets have been developed and widely adopted as reference layers in magnetic tunnel junctions. They are composed of two ferromagnetic layers coupled antiferromagnetically through a thin non-magnetic spacer (e.g., Ruthenium, Rhodium, or Iridium) via RKKY exchange coupling. Synthetic antiferromagnetsprovide multiple advantages: improved magnetic stability, reduced dipolar interactions (especially when the two ferromagnetic layers are magnetically compensated, eliminating stray fields), enhanced thermal robustness, and the potential for higher areal density and more compact device architectures.

For optimal magnetic tunnel junction performance, synthetic antiferromagnetsstructures exhibiting stronger antiferromagnetic coupling – i.e. larger RKKY exchange fields –are desirable, as they allow for a wider magnetic field window to pin the free layer magnetization without inducing unwanted magnetic interactions. Despite recent progress in the field, electric current-based magnetization switching schemes in magnetic tunnel junctions still pose challenges in terms of energy efficiency. Significant reduction of ohmic loss is envisaged by using voltage (or electric fields), instead of current, to control magnetism.

Thus, it is clear that the reported modulation of antiferromagnetically RKKY coupled multilayers with electric field is of great interest and technological relevance for magnetoresistive random access memory (MRAM) development. Magneto-ionic control of RKKY interactions offers a versatile platform for developing next-generation spintronic devices with low power consumption, non-volatility, and dynamic reconfigurability. By enabling voltage-driven tuning of interlayer magnetic coupling, this approach holds promise for applications in voltage-controlled MRAM, neuromorphic computing, and spintronic logic, where analog modulation and multi-state behavior are desirable. It also enhances the performance of magnetic sensors and spin valves by stabilizing antiparallel states and reducing power demands.

Read more on ALBA website

BESSY II: Heterostructures for Spintronics

BESSY II: Heterostructures for Spintronics

Spintronic devices work with spin textures caused by quantum-physical interactions. A Spanish-German collaboration has now studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures. This could lead to new spintronic devices based on these materials.

Spintronics uses the spins of electrons to perform logic operations or store information. Ideally, spintronic devices could operate faster and more energy-efficiently than conventional semiconductor devices. However, it is still difficult to create and manipulate spin textures in materials.

Graphene for Spintronics

Graphene, a two-dimensional honeycomb structure build by carbon atoms, is considered an interesting candidate for spintronic applications. Graphene is typically deposited on a thin film of heavy metal. At the interface between graphene and heavy metal, a strong spin-orbit coupling develops, which gives rise to different quantum effects, including a spin-orbit splitting of energy levels (Rashba effect) and a canting in the alignment of spins (Dzyaloshinskii-Moriya interaction). Especially the spin canting effect is needed to stabilise vortex-like spin textures, known as skyrmions, which are particularly suitable for spintronics.

Plus Cobalt Monolayers

Now, however, a Spanish-German team has shown that these effects are significantly enhanced when a few monolayers of the ferromagnetic element cobalt are inserted between the graphene and the heavy metal (here: iridium). The samples were grown on insulating substrates which is a necessary prerequisite for the implementation of multifunctional spintronic devices exploiting these effects.

Read more on HZB website

Image: Symbolic illustration of a graphene layer on a microchip. In combination with a heavy-metal thin film and ferromagnetic monolayers, graphene could enable spintronic devices.

Credit: Dall-E/arö

Mechanisms of electrical switching in antiferromagnets

Mechanisms of electrical switching in antiferromagnets

The electronic devices we use on a day-to-day basis are powered by electrical currents. Data processing and computation also relies on information provided by electrons. This is what we call electronics. In recent years, a new field called spintronics emerged to overcome the limitations of traditional electronics, offering a leap towards high-density data storage and ultrafast computing dynamics. Spintronics employs a different concept. Instead of store information using the charge of electrons of the materials, the spintronic approach is to exploit their magnetic moment, in other words, their spin, to store and process information – aiming to make the computers of the future more compact, fast, and sustainable.

Antiferromagnets are considered very promising materials for future spintronic applications, offering unique properties to overcome limitations posed by current systems using ferromagnets. Lack of stray fields favor denser packing and high internal frequencies could allow faster operation. However, these properties at the same time make it more difficult to operate in terms of writing information, i.e. the switching part.

Now, a study lead by researchers from the Johannes Gutenberg University Mainz (Germany), in collaboration with the Tohoku University, the University of Tokyo (Japan) and the ALBA Synchrotron aims to understand the underlying antiferromagnetic switching mechanisms. The study disentangles two different switching mechanisms in an antiferromagnet material -cobalt (II) oxide or CoO- when subjected to a current pulse. One is due to the fundamental spin-orbit torque and the other is a heat-induced thermomagnetoelastic effect.


Read more on the ALBA website

Image: XMLD-PEEM imaging of cobalt (II) oxide (CoO) sample after the application of high current-density pulses along different directions, revealing two different switching mechanisms. Images obtained at CIRCE beamline of the ALBA Synchrotron.

A Novel Staircase Pattern in Spin-Stripe Periodicity

A Novel Staircase Pattern in Spin-Stripe Periodicity

SCIENTIFIC ACHIEVEMENT

At the Advanced Light Source (ALS), striped patterns of spins in a magnetic thin film were found to evolve under an applied magnetic field in steps reminiscent of a structure known as the “Devil’s Staircase.”

SIGNIFICANCE AND IMPACT

Such studies are valuable for understanding competing interactions at the atomic level for applications such as magnetic sensors and spintronic devices.

Devilishly complex systems

The “Devil’s Staircase” is a peculiar mathematical function that rises continuously but has no slope (i.e., its derivative is zero almost everywhere). This is because it consists of “runs” (flat sections) connected by “rises” that are fractal: each contains successively smaller copies of the main step, to the infinitesimal limit. Similar structures have emerged in phenomena ranging from earthquakes to charge density waves—systems characterized by competing pressures that result in periods of stability punctuated by short bursts of activity.

Here, researchers report the observation of novel staircase patterns in the evolution of spin-stripe domains in an iron/gadolinium (Fe/Gd) multilayer system. Theoretical modeling that builds on the measurements revealed which of the competing atomic-level interactions in this system is the dominant cause of the staircase structure. The findings help unravel the complex interplay of forces affecting spins in systems relevant to applications in magnetic sensing, information storage, and spintronics.

Read more on the ALS website

Image: A scattering image of one of the sample’s magnetic phases

Revealed: 3D magnetic configuration of ferrimagnetic multilayers with competing interactions

Revealed: 3D magnetic configuration of ferrimagnetic multilayers with competing interactions

Researchers from the Physics Department of the Universidad de Oviedo, CINN-CSIC and HZB, in collaboration with ALBA, have explored the magnetic configuration of ferrimagnetic structures often employed to build modern spintronic devices and magnetic recording media. At the MISTRAL beamline of ALBA, using vector magnetic tomography, a magnetic trilayer fabricated at Oviedo was characterized. These findings will permit to generate precise physical models describing the magnetic behaviour of this type of systems and control and exploit them for the design of spintronics and magnetic storage devices.

 Modern spintronic devices and magnetic recording media often consist of complex magnetic structures. These structures are designed by precisely adjusting magnetic interactions as exchange, anisotropies and magnetostatics to achieve specific characteristics.

A collaboration between researchers from the Physics Department of the Universidad de Oviedo, the Centro de Investigación en Nanomateriales y Nanotecnología (Oviedo), the Helmholtz Zentrum Berlin für Materialien und Energie (Berlin) and the ALBA Synchrotron have investigated a combination of ferrimagnetic structures, often employed to build this type of devices. 

At the MISTRAL beamline of ALBA, a dichroic vector magnetic tomography of the device was performed and it revealed details of complex magnetisation configurations of the sample. The importance of synchrotron light lies in the fact that this information is currently impossible to evidence with other techniques when studying magnetic thin films.

The ability to characterize the configuration of the magnetisation in complex structures with competing magnetic interactions will permit to generate precise physical models describing the magnetic behaviour of these systems. Thus, experts will be able to control and exploit them for the design of spintronics and magnetic storage devices.

Read more on the ALBA website

Image: Magnetisation obtained from the magnetic tomography data at the MISTRAL beamline.

Unusual electronic properties taking shape

Unusual electronic properties taking shape

In a recent study, an international team led by researchers from The Pennsylvania State University in the US investigated the one-dimensional (1D) material tantalum selenide iodide (TaSe4 )2I. Its electronic properties had been theoretically predicted but not observed experimentally before the study conducted at the Bloch beamline. Evaporating iodine atoms turn out to drive unforeseen electronic changes.

Materials with unusual electronic properties such as charge density waves or topological states push the understanding of the fundamentals of quantum matter. They are also exciting candidates for the next generations of energy-efficient electronic and spintronic devices.

In the present study, the researchers found that the electronic properties of (TaSe4 )2I were different from the theoretical prediction. The band structure of a material can loosely be compared to a map of the material’s electronic properties. (TaSe4 )2I has something called Dirac bands, which is often found in this type of materials. The prediction said that the Dirac bands would split due to Weyl physics, which is not the case. The bands split with temperature, and the driver behind it is iodine atoms evaporating from the material’s surface.

Read more on the MAX IV website

Image: Surface charge induced Dirac band splitting in 1D material (TaSe4 )2I