Tag: spins

Controlling magnetic waves in a spin liquid

Controlling magnetic waves in a spin liquid

Scientists at the Paul Scherrer Institute PSI have shown that excitation of a spin liquid with intense THz pulses causes spins to appear and align within less than a picosecond. This induced coherent state causes a magnetic field to form inside the material, which is detected using ultrashort X-ray pulses at the X-ray Free Electron Laser SwissFEL.  

Spins carried by atoms are the building blocks of magnetism. In a ferromagnet, they all align in the same direction, a feature used to store data on hard drives. In antiferromagnets, they form an antiparallel alignment. Like the surface of a stormy sea where water mountains build up here and there, disappearing as fast as they come, the spins in a spin liquid are fluctuating and form no ordered magnetic state despite local interactions.  

Scientists at PSI have shown that the electromagnetic field of short THz pulses imprints its coherence onto the orbital wavefunctions of Terbium atoms of a Tb2Ti2O7 crystal, causing the spins of 1015 Tb excited ions in the material to appear and move synchronized, reminiscent of how wind can create highly periodic patterns of waves. This created state is called an ensemble of coherent quantum states. 

Read more on PSI website

Image: Artistic impression of a magnetic moment appearing in a spin liquid after excitation with an intense short THz pulse

Credit: Roman Mankowsky.

Spintronics: A new path to room temperature swirling spin textures

Spintronics: A new path to room temperature swirling spin textures

A team at HZB has investigated a new, simple method at BESSY II that can be used to create stable radial magnetic vortices in magnetic thin films.

In some materials, spins form complex magnetic structures within the nanometre and micrometre scale in which the magnetization direction twists and curls along specific directions. Examples of such structures are magnetic bubbles, skyrmions, and magnetic vortices. Spintronics aims to make use of such tiny magnetic structures to store data or perform logic operations with very low power consumption, compared to today’s dominant microelectronic components. However, the generation and stabilization of most of these magnetic textures is restricted to a few materials and achievable under very specific conditions (temperature, magnetic field…).

A new approach

An international collaboration led by HZB physicist Dr Sergio Valencia has now investigated a new approach that can be used to create and stabilize complex spin textures, such as radial vortices, in a variety of compounds. In a radial vortex, the magnetization points towards or away from the center of the structure. This type of magnetic configuration is usually highly unstable. Within this novel approach radial vortices are created with the help of superconducting structures while their stabilization is achieved by the presence of surface defects.

Superconducting YBCO-islands

Samples consist of micrometer size islands made of the high-temperature superconductor YBCO on which a ferromagnetic compound is deposited. On cooling the sample below 92 Kelvin (-181 °C), YBCO enters the superconducting state. In this state, an external magnetic field is applied and immediately removed. This process allows the penetration and pinning of magnetic flux quanta, which in turn creates a magnetic stray field. It is this stray field which produces new magnetic microstructures in the overlying ferromagnetic layer: spins emanate radially from the structure centre, as in a radial vortex.

Read more on HZB website