ALTERMAGNETISM — A new form of Magnetism
Traditional Magnetic Classification
For over a century, magnetism was divided into two broad categories:
Type | Description | Example/Features |
Ferromagnetism | Magnetic moments of atoms align parallelly, producing a strong external magnetic field. | Iron, Nickel, Cobalt; used in hard drives, magnets. |
Antiferromagnetism | Magnetic moments align antiparallel, cancelling each other’s field, producing no net magnetisation. | Manganese oxide, Chromium. |
Emergence of Altermagnetism (2019–2024)
Proposed theoretically in 2019, confirmed experimentally in 2024.
Represents a third fundamental form of magnetism distinct from the above two.
Example materials: Manganese Telluride (MnTe) and Ruthenium Dioxide (RuO₂).
Key Characteristics
Property | Description |
Crystal Symmetry | Opposing magnetic spins are related not by translation (as in antiferromagnets), but by rotation or mirror-flip symmetry. |
Net Magnetisation | Zero — no external magnetic field (like antiferromagnets). |
Internal Spin Structure | Electron bands are spin-split (like ferromagnets). This enables spin-polarised currents. |
Spin Splitting | Up-spin and down-spin electrons have slightly different energy levels; allows control of electron spin without external fields. |
Speed | Potential switching speeds in terahertz (THz) range (1000× faster than gigahertz ferromagnetic systems). |
Measurement Techniques | Angle-Resolved Photoemission Spectroscopy (ARPES) and X-ray Magnetic Dichroism are used since it has no external magnetic field. |
Anomalous Hall Effect | Some altermagnets exhibit a measurable voltage (Hall effect) without net magnetisation, making them easier to detect electronically. |
Importance and Applications
Sector | Benefits |
Spintronics | Enables spin-polarised currents with zero stray magnetic field → compact, fast, energy-efficient devices. |
Quantum Computing | Reduces magnetic noise in superconducting circuits. |
Microelectronics | Ideal for miniaturised memory and logic elements (no field interference between components). |
Challenges
Difficulty in synthesising single-domain altermagnetic materials.
Need for high-quality crystal growth and domain control.
Must develop scalable and low-cost fabrication for commercial integration.
Examples of Altermagnetic Materials
Manganese Telluride (MnTe) — confirmed via ARPES in 2024.
Ruthenium Dioxide (RuO₂) — key material in further experiments.
Theoretical predictions include various metals, semiconductors, insulators, and organic crystals.
Significance
Represents a new magnetic phase beyond traditional models.
Merges properties of ferromagnets (spin-splitting) and antiferromagnets (no net magnetisation).
Potential to revolutionise spintronics, quantum devices, and high-speed computing.
Comparision
Property | Ferromagnetism | Antiferromagnetism | Altermagnetism |
Spin alignment | Parallel | Antiparallel | Antiparallel (mirror/rotation symmetry) |
Net magnetisation | High | Zero | Zero |
Spin-splitting | Yes | No | Yes |
External field | Present | Absent | Absent |
Example | Iron | Manganese oxide | MnTe, RuO₂ |
Key technique | Magnetometer | Neutron diffraction | ARPES, X-ray dichroism |
Applications | Data storage | Sensors | Spintronics, Quantum tech |
Prelims Practice MCQs
Q. Which of the following best describes the term Altermagnetism?
A. Magnetic order where all atomic spins align parallelly.
B. A state with alternating magnetic spins related by mirror or rotational symmetry, showing no net magnetisation but spin-polarised bands.
C. Magnetic state showing complete randomness in spin directions.
D. Weak magnetism caused by electron orbital motion only.
Answer: B.
Explanation:
Altermagnetism involves antiparallel spins connected by rotation or reflection, not translation, resulting in no net field but spin-split bands.
Q. What is the Anomalous Hall Effect observed in Altermagnets?
A. Formation of a magnetic monopole in the crystal structure.
B. Generation of an electric voltage transverse to current without external magnetic field.
C. Increase in magnetic susceptibility with temperature.
D. Decrease in electrical resistance under strong magnetic field.
Answer: B.
Explanation:
In altermagnets, a sideways voltage (Hall voltage) appears due to spin-dependent electronic structure — even though the material has zero net magnetisation.
Q. Which of the following is/are potential applications of Altermagnetic materials?
Spintronic devices
Quantum computing systems
Superconducting magnets
Optical fibre communication
Select the correct code:
A. 1 and 2 only
B. 1, 2, and 3
C. 1, 2, and 4
D. 1 only
Answer: A. 1 and 2 only
Explanation:
Altermagnets’ zero stray fields and spin control make them suitable for spintronics and quantum devices.
Not directly used in superconducting magnets or optical fibre systems.