First altermagnet

Context : Researchers from S.N. Bose National Centre and the Indian Association for the Cultivation of Science have discovered that chromium-antimony (CrSb), a stable and easily synthesizable magnetic compound, exhibits direction-dependent conduction polarity (DDCP). This means it conducts electrons along one direction and holes along another, allowing it to act as both n-type and p-type material in devices.

This marks CrSb as the first-known altermagnet—a newly identified magnetic class—showing DDCP. Altermagnets have no overall magnetism due to cancelling spins but show spin-dependent charge behaviour, making them promising for spintronics and thermoelectric devices.

Additionally, 2% vanadium doping turned CrSb uniformly p-type, aligning with theoretical predictions. This dual-polarity and tunability of CrSb opens avenues for compact, multifunctional electronics using a single crystal.

What are n-type and p-type materials?

• n-type materials conduct electricity using electrons (which are negative).

• p-type materials conduct using “holes” (which act like positive charges).

Direction-Dependent Conduction Polarity (DDCP)

• Definition: A material property where charge carriers (electrons or holes) dominate in one direction but not in others.

• Normal Materials:

  • Conduct electricity using either:

    • Electrons (n-type)

    • Holes (p-type)

  • This property is usually uniform in all directions.

• DDCP Materials:

  • Electron-dominant in one direction (e.g., along the plane)

  • Hole-dominant in another direction (e.g., vertical axis)

  • Acts as both n-type and p-type in the same crystal depending on the direction.

Significance of DDCP Materials

• Can function as both halves of a p-n junction in electronic or thermoelectric devices without needing two different materials.

• Useful in miniaturized and multifunctional electronics.

Discovery & Material Used

Chromium-Antimony (CrSb)

• Nature: A magnetic compound made from common and inexpensive elements.

• Discovery: By researchers from:

  • S.N. Bose National Centre for Basic Sciences

  • Indian Association for the Cultivation of Science

• Crystal Growth: Single crystals of CrSb were synthesized using chemical vapor transport in sealed quartz tubes.

Testing Techniques

(a) Hall Effect

• Used to detect the dominant charge carrier in a material.

• When a magnetic field is applied, it bends the path of charge carriers.

• Helps identify if electrons (negative) or holes (positive) are carrying the current.

(b) Seebeck Effect

• Occurs when there is a temperature gradient across a material, causing a voltage to appear.

• Sign of the voltage indicates whether electrons or holes are the majority carriers.

• CrSb showed:

  • Electrons dominate along the plane

  • Holes dominate along the vertical axis

Altermagnets: 

What is an Altermagnet?

• A recently discovered magnetic state.

• Atomic spins are arranged in such a way that they cancel out each other (net magnetic moment is zero).

• Despite no overall magnetism, electrons with different spins behave differently due to crystal structure.

• Key for spintronics: a field that uses electron spin (not just charge) to store and process data.

CrSb: First Altermagnet with DDCP

• First material discovered that is both an altermagnet and exhibits DDCP.

• Easily synthesizable and stable, unlike previous DDCP materials.

Implications & Future Applications

• Electronics & Thermoelectrics:

  • A single CrSb crystal could replace traditional p-n junctions.

• Spintronic Devices:

  • Use spin behavior for faster and more efficient memory and logic devices.

Tuning the Material:

• Replacing 2% of Cr with Vanadium (V):

  • Turned the whole crystal into p-type.

  • Matched with theoretical predictions.

  • Shows that the material's properties are tunable.