Task 4: Lateral spin transport and spin waves including devices

4.1-B Novel devices based on Heusler films with GMR and MTJ nanocontacts (Ando, Naganuma, Oogane – Sendai)

This project focuses on the preparation of GMR and TMR nano-contacts with diameters significantly lower than 100 nm to films of Heusler compounds. Some of the Heusler alloys show very low magnetic damping compared to conventional materials. When we use the Heusler alloys as the bottom electrode, it must be an advantage to transport spin waves on it. The structures can generate magnetization precession under certain conditions when a dc current is flowing through the GMR/TMR stack. In order to confirm the propagation of spin waves in the bottom electrode, we prepare nano-contacts with various distances between them. We can check the mode locking of the magnetization oscillation of the contacts. The goals of this project is to obtain the appropriate stacking structure and the arrangement of the GMR and TMR nano-contacts in order to achieve strong and sharp signal output from this device.

4.3-B Lateral spin transport in semiconductors (Matsukura, Kohda, Nitta – Sendai)

This project focuses on the establishment of efficient generation and sensitive detection of spin current, and the investigation of spin dynamics in semiconductor lateral devices combined with ferromagnetic semiconductors and/or Heusler materials. The advantage of using semiconductors for spintronic devices is that the spin states can be manipulated by electrical and optical means. The systematic study on gate voltage dependence of spin states is expected to provide useful information, such as the effect of the Rashba and the Dresselhaus spin-orbit interactions on spin dynamics, which is important to realize the long spin coherence with the short spin flip time. In order to demonstrate new functional device operation, the optimization of device structures by selecting appropriate combination of semiconducting and Heusler materials will be done.

4.5-A Heusler materials for new spin transport applications (Jakob, Felser – Mainz)

This project combines the design of new semiconducting Heusler compounds with new transport phenomena. The goal is to design new materials usable in devices for lateral spin transport and the realization of such devices. The materials for new magneto resistive devices are based on half metallic Heusler compounds combined with new semiconducting Heusler compounds. The combination of half metallic and semiconducting Heusler films will render a pure spin current possible. For lateral spin transport, materials with a large spin diffusion length are essential. The diffusion length is expected to be large in Heusler compounds providing a band gap at the Fermi energy and possessing a low spin orbit coupling. With ever increasing miniaturization non-local effects will become important in next generation devices. The final aim will be to demonstrate spin accumulation effects in lateral devices using new materials.

4.6-B Lateral spin transport in Heusler alloy systems (Takanashi, Sakuraba – Sendai)

Compared with a current-perpendicular-to-plane (CPP) structure, a lateral structure consisting of ferromagnetic material (FM) and nonmagnetic material (NM) has a high degree of freedom in the device structure to create and control spin-current. For example, spin-MOSFET using FM source and drain and Si channel has been proposed and attracted much interest as a useful application. Therefore, spin-injection into NM including semiconductor is a challenging subject in recent and future spintronics field. Half-metallic Heusler alloys are promising candidates as an injector and detector of spin-current because of their large spin-polarization. In addition, Heusler-type semiconductors, such as CoTiSb and FeVSb, are expected as novel, potential NM materials, because of their small structural and electronic mismatch with half-metallic Heusler alloys. The central goals of this project are (i) to fabricate lateral spin-valve structure with half-metallic Heusler alloy films with non-magnetic metals and semiconductors and (ii) investigate the lateral spin-transport properties. One of the important challenges in this project is to inject spin-current to a Heusler-type semiconductor from a half-metallic Heusler alloy.

4.7-B Nonlinear spin-wave dynamics and radiation properties of small Heusler devices (Serga, Hillebrands - Kaiserslautern)

This project explores fundamental issues of nonlinear spin dynamics and spin-wave radiation in Heusler compound based structures. Some novel Heusler materials developed in the ASPIMATT Reseach Unit and the preceding FG559 Research Unit exhibit very low magnetic damping and high spin polarization compared with ordinary 3d magnetic metals and alloys (e.g. Permalloy and CoFe). These special material properties permit increased spin-wave propagation distances and give rise to lower nonlinear thresholds, opening doors to new types of spin-wave devices. Moreover, Heusler compounds offer new possibilities for spin-torque based systems operating at reduced driving currents. Using the technique of Brillouin light scattering microscopy, this project will investigate two interconnected issues: a) nonlinear spin-wave mode formation and coupling in patterned Heusler films externally driven by microwave magnetic fields, and b) nonlinear spin-wave excitation, radiation, and propagation (including magnetic bullet formation) in Heusler-based spin-valve nanocontact spin-torque oscillators prepared in Project 4.1-B  (Ando, Naganuma, Oogane). These processes will be studied in the context of potential device applications such as microwave oscillators for chip-to-chip or intra-chip communication, and direct spin-wave based information transfer.