Every electron is like a spinning top: it twirls around its own axis. This rotation is called spin. In conventional electronics, we don't use spin — only charge. But that's a missed opportunity: if we learn to control spin, chips could become faster and more efficient. The problem is that in silicon, the main material of electronics, spin is quickly lost, especially in p-type silicon, where charge is carried by "holes."
Researchers in Japan have found a way to extend spin's lifetime. They took a layer of p-type silicon and placed a magnetic material, Mn2CoAl, on top: it's a so-called spin gapless semimetal. Between them, they inserted a thin film of magnesium oxide, which helps electrons with the right spin hop into the silicon. The result is a pathway where spin can travel without getting lost.
The scientists measured how long the spin persists. At room temperature, it's 0.68 nanoseconds. That's short, but enough to send a signal about a micron. When cooled to 5 K, the spin lasts even longer—4.11 nanoseconds. The temperature dependence is weak, pointing to a specific relaxation mechanism — Bir–Aronov–Pikus. In simple terms, spin is lost due to interaction with "holes," not impurities.
This result matters for the future: if spin can be preserved in silicon at room temperature, we could build spin transistors and memory that consume far less energy. Silicon is already in every fab — no need to invent new materials, just add a magnetic layer.
as written by the authors arXiv:2602.13118
Electrical spin injection and transport in silicon are central challenges for realizing semiconductor-based spintronic devices, particularly in p-type Si, where strong spin relaxation and interface effects often suppress detectable spin signals. Here, we report electrical spin injection, accumulation, and transport in lightly doped p-type silicon using the spin-gapless Heusler compound Mn$$_2$$CoAl as a ferromagnetic spin injector, separated from the p-Si channel by a thin MgO tunnel barrier in a lateral device geometry. Spin transport is systematically investigated through three-terminal (3-T) Hanle and four-terminal (4-T) nonlocal (NL) spin-valve and Hanle measurements. Clear Lorentzian Hanle signals are observed in the 3-T configuration from 5 K up to room temperature, yielding a spin lifetime of $$\sim$$0.68 ns at 300 K that increases to $$\sim$$4.11 ns at 5 K. Temperature-dependent analysis reveals a weak power-law dependence of the spin lifetime, indicating Bir--Aronov--Pikus--type spin relaxation mechanism. To validate genuine spin transport, NL spin-valve and Hanle measurements were performed, revealing well-defined spin-valve switching and controlled spin precession at 5 K. From NL Hanle fitting, a spin lifetime of $$\sim$$5.65 ns and a spin diffusion length of $$\sim$$0.82 $$\mu$$m are extracted, confirming diffusive long-range spin transport in the p-Si channel. Although NL signals diminish at elevated temperatures due to reduced interfacial spin polarization and thermal noise, the combined 3-T and 4-T results establish spin-gapless Mn$$_2$$CoAl as an effective spin injector for p-type silicon. These findings highlight the potential of spin-gapless semiconductors for improving spin injection efficiency and advancing Si-compatible spintronic devices.
Mn2CoAl is a spin gapless semimetal: electrons with one spin direction move freely, while those with the opposite spin are blocked. It's like a subway turnstile that only lets people through in one direction.