Building electronic devices that work without needing to actually transport electrons is a goal of spintronics researchers, since this could lead to: reduced power consumption, lower levels of signal noise, faster operation, and denser information storage. However, the generation of pure spin currents remains a challenge. Now, YoshiChika Otani and colleagues at the RIKEN Advanced Science Institute, Wako, and five other research institutes in Japan and China, have produced a large spin current in an important spintronic device called a lateral spin valve.
They Tlowered junction resistance by a factor of up to 1,000, and increased the efficiency of spin injection into the silver wire. As a result, the output voltage reached 220 microvolts, which is more than 100 times greater than that of existing devices. In addition, the research team was able to observe the injected spins rotating, of what is technically known as precessing, in response to a magnetic field along the entire length of their 6-micrometer silver wire, confirming high spin injection efficiency.
The spin valve could be further improved, says Otani, by using cobalt–iron ferromagnets, which are known to have greater spin injection efficiency than nickel–iron, with potential near-term application as sensors in high-density magnetic media.
In this lateral spin valve, a current is applied to a ferromagnetic nickel–iron contact (pink), in which spins are aligned in a particular direction. A thin layer of magnesium oxide (green) separates the contact from a non-magnetic silver wire (yellow). While both spin and charge current flow to the left (blue arrow), only spin current flows to the right (black arrow).
The non-local spin injection in lateral spin valves is strongly expected to be an effective method to generate a pure spin current for potential spintronic application. However, the spin-valve voltage, which determines the magnitude of the spin current flowing into an additional ferromagnetic wire, is typically of the order of 1 μV. Here we show that lateral spin valves with low-resistivity NiFe/MgO/Ag junctions enable efficient spin injection with high applied current density, which leads to the spin-valve voltage increasing 100-fold. Hanle effect measurements demonstrate a long-distance collective 2π spin precession along a 6-μm-long Ag wire. These results suggest a route to faster and manipulable spin transport for the development of pure spin-current-based memory, logic and sensing devices.