Why in news?
Researchers at the S.N. Bose National Centre for Basic Sciences, Kolkata, discovered that chromium antimonide (CrSb) exhibits a phenomenon called direction‑dependent conduction polarity (DDCP). This means the same crystal conducts electricity like an n‑type semiconductor along its layers but like a p‑type semiconductor across them. The discovery identifies CrSb as an altermagnet with potential to revolutionise spintronics.
What are altermagnets?
- They are materials that combine properties of ferromagnets (high spin–orbit splitting) and antiferromagnets (zero net magnetisation). Their unique symmetry leads to spin polarisation that changes direction depending on the crystal axis.
- In altermagnets, opposite spin currents flow in different directions without producing a net magnetic field. This permits spintronic applications without stray magnetic interference.
Key features of CrSb discovery
- Direction‑dependent conduction: Hall effect and Seebeck coefficient measurements showed that CrSb carries electrons along the hexagonal layers (n‑type) but holes across them (p‑type). This arises from the anisotropic band structure – electron pockets dominate in‑plane transport, while hole pockets dominate out‑of‑plane transport.
- Zero net magnetism: Despite exhibiting long‑range magnetic ordering, CrSb has no net magnetic moment because spins cancel each other out; this reduces magnetic noise.
- High spin splitting: Band structure calculations show spin splitting about 30 times larger than room temperature energy (30 × kT), enabling robust spintronic operations at ambient conditions.
- Thermal stability: Altermagnetism persists well above room temperature, making it attractive for devices.
Potential applications
- Spintronics: Devices based on electron spin rather than charge can achieve lower power consumption and higher data speeds. The ability to generate spin currents without magnetic fields could simplify design.
- Compact electronics: Direction‑dependent conduction allows integration of p‑type and n‑type behaviour in a single material, reducing component count in circuits.
- Thermoelectric devices: The unique Seebeck response may enable efficient energy conversion in power generation and refrigeration.
- Sustainable electronics: As CrSb is non‑toxic and abundant, it may offer environmentally friendly alternatives to rare earth magnets.