Spintronics: Resetting the future of Heat Assisted Magnetic Recording
The nanostructured membrane has a honeycomb pattern with nanoholes of 68 nm in diameter. The nanoholes pin down the magnetic domains. © HZB
A thin film of Dysprosium-Cobalt (green) has been sputtered on top of the membrane, resulting in an array of antidots. The magnetic moments of DyCo5 are perpendicular to the plane and stable against external magnetic fields. A laser pulse can be used to locally increase the temperature of individual bits. © HZB
Moderate heating up to 80 °Celsius does tilt the magnetic moment associated to a single bit into the plane. Upon cooling to room temperature, the magnetic moment stays in plane, until it is overwritten by a magnetic writing head. © HZB
A HZB team has examined thin films of Dysprosium-Cobalt sputtered onto a nanostructured membrane at BESSY II. They showed that new patterns of magnetization could be written in a quick and easy manner after warming the sample to only 80 °Celsius, which is a much lower temperature as compared to conventional Heat Assisted Magnetic Recording systems. This paves the way to fast and energy efficient ultrahigh density data storage. The results are published now in the new journal Physical Review Applied.
To increase data density further in storage media, materials systems with stable magnetic domains on the nanoscale are needed. For overwriting a specific nanoscopic region with new information, a laser is used to heat locally the bit close to the so called Curie-Temperature, typically several hundred degrees Celsius. Upon cooling, the magnetic domain in this region can be reoriented in a small external magnetic field, known as Heat Assisted Magnetic Recording (HAMR). In industry, Iron-Platinum materials are currently used as magnetic media for the development of such HAMR-data storage devices.
Magnetic signals mapped at BESSY II before and after heating
A HZB team has now examined a new storage media system of Dysprosium and Cobalt, which shows key advantages with respect to conventional HAMR materials: A much lower writing temperature, a higher stability of the magnetic bits, and a versatile control of the spin orientation within individual magnetic bits. They achieved this by sputtering a thin film of Dysprosium and Cobalt onto a nanostructured membrane. The membrane was produced by scientific cooperation partners at the Institute of Materials Science of Madrid. The system shows a honeycomb antidot pattern with distances of 105 nanometers between nanoholes, which are 68 nanometers in diameter. These nanoholes act themselves as pinning centers for stabilizing magnetic wall displacements. The magnetic moments of DyCo5 are perpendicular to the plane and stable against external magnetic fields.
Energy efficient process
HZB-physicist Dr. Jaime Sánchez-Barriga and his team could demonstrate that warming the system to only 80 degrees Celsius is sufficient to tilt the magnetic moments in the DyCo5 film parallel to the surface plane. With measurements at the PEEM and XMCD instruments at BESSY II they could map precisely the magnetic signals before, during and after warming. After cooling to room temperature it is then easy to reorient the magnetic domains with a writing head and to encode new information. “This process in DyCo5 is energy efficient and very fast”, states Dr. Florin Radu, co-author of the study. “Our results show that there are alternative candidates for ultrahigh density HAMR storage systems, which need less energy and promise other important advantages as well”, adds Sánchez-Barriga.
Publication: Ferrimagnetic DyCo5 nanostructures for bits in heat-assisted magnetic recording. A. A. Ünal, S. Valencia, F. Radu, D. Marchenko, K. J. Merazzo, M. Vázquez, and J. Sánchez-Barriga, Phys. Rev. Applied 5, 064007
Doi: http://dx.doi.org/10.1103/PhysRevApplied.5.064007
- Magnetic imaging: Micro-flowers increase the local magnetic fieldMaterials with magnetic nanostructures have many potential applications such as in spintronics. To explore such materials, nanoscale magnetic-sensitive imaging techniques are very useful, but up to now only weak magnetic fields could be applied during the imaging process. Now an international collaboration led by Dr. Sergio Valencia, HZB, has developed an approach that overcomes this limitation. The team designed tiny magnetic flux concentrators (MFCs), into which the sample is placed. The geometry of the MFCs resembles a flower with a number of petals which focus the applied magnetic field into its center. This greatly expands the magnetic field range available during imaging, and so the range of magnetic systems that can be investigated. The micro-flowers, enhancing magnetic fields locally, can find application in different nanometric magnetic microscopy techniques.
- CIGS-perovskite tandem cell achieves record efficiency of 25.5 %A Berlin-based team from HZB and Center for the Science of Materials Berlin (CSMB) at the Humboldt-Universität zu Berlin has set a new record for a tandem solar cell. Using a combination of a CIGS semiconductor layer and perovskite, along with several optimised intermediate layers, they were able to convert 25.5% of sunlight into electrical energy. The previous record for this combination of materials and this size of cell stood at 24.6%. The new record has been certified and is visible in the prestigious Solar Cell Efficiency Tables (the "Green Tables"), which serve as the definitive ledger for the global photovoltaic community.
- Disorder creates new properties in compound semiconductorsAn international research team has demonstrated that the intrinsic disorder of the compound semiconductor CuInSnS₄ can be exploited to influence its optical properties. While the atomic vibrations also sense the local disorder, their response is averaged over many different local environments and therefore appear isotropic, as expected for a cubic crystal. In contrast, the optical excitations, known as excitons, are much more sensitive to the local arrangement of atoms. Surprisingly, they show a direction-dependent optical response even though the average crystal structure is cubic. These findings shed new light on the relationship between disorder and material properties, opening up new options for targeted 'disorder engineering' in optoelectronic and photocatalytic devices.