Process development for a metallic spin flip based laser fabrication

Integration of novel magnetic nanodevices into conventional electronic circuits is the main aim of research and development in the new eld referred to as Spintronics. Spin-valves and Magnetic Random Access Memory (MRAM) are examples of already developed spintronic devices. In this work the aim is to develop a fabrication process for a novel spin laser device. Exploiting the high electron density combined with the intrinsic energy splitting between the two spin sub-bands in a ferromagnetic metal makes it possible in principle to obtain a metallic laser with an high optical gain. The emission frequency would be determined by the exchange energy spitting for a given ferromagnet used in fabricating the laser device. A theoretical description as well as experimental results indicating spin- ip photon emission processes for single magnetic point contacts have been reported recently. Based on these results, a spin laser device is designed and fabricated the main focus of this work. A disk-shaped resonator containing an array of magnetic point contacts was patterned using a colloidal lithography process combined with conventional photolithography. Using colloidal lithography allowed to pattern a SiO2/Al-mask with a self-assembled hexagonal nanostructure. The mask consisted of an array of apertures with diameter 10-15 nm separated by 200 nm. The holes are subsequently lled with FeCr and Fe so that magnetic point contacts of size about 10 nm were obtained. The micrometer scale disk-shaped resonators enclosing the point contact arrays were patterned by optical lithography. Resonators with diameters from 10 µm to 50 µm were fabricated. Four-point electrical measurements have been done on the integrated devices, with contact pads to resonators containing point contact arrays. The device resistance R as well as their di erential resistance dV/dI have been measured. About 10% of the samples showed excitations in R and dV/dI very similar to the ones measured in previous works on single magnetic PCs. Current-Induced Hysteretic Switching as well as Current Induced Spin-Transfer Torque were thus detected in the fabricated arrays. Moreover, in a few samples large excitations at high bias voltages were measured. They are characterized by a 2-fold increase in the resistance, with a threshold character in bias voltage, which is typical of laser devices. A direct con rmation of lasing in the devices fabricated will be future optical measurements in the terahertz range, where the spin- ip radiation is expected.