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Ferro vs antiferromagnetic; magnetostriction

Short answer

Ferromagnetic materials have parallel spin alignment and spontaneous net magnetization (e.g., Fe, Co, Ni). Antiferromagnetic materials have antiparallel spins, zero net magnetization (e.g., MnO, FeO). Magnetostriction is the change in dimensions of a ferromagnet when magnetized, caused by domain rotation and spin-orbit coupling, with strain λ ≈ 10⁻⁶–10⁻⁵ (Ni contracts).

Distinguish between ferromagnetic and anti-ferromagnetic materials with suitable examples of each. Explain magnetostriction with neat diagram.

Ferromagnetic vs antiferromagnetic

PointFerromagneticAntiferromagnetic
Spin alignmentParallelAntiparallel, equal
Net magnetizationLarge, spontaneousZero
χ\chiVery largeSmall, positive
Critical temperatureCurie TCT_CNéel TNT_N
HysteresisYesNo
ExampleFe, Co, NiMnO, FeO, NiO, Cr
 Ferro: ^ ^ ^ ^     Antiferro: ^ v ^ v

Magnetostriction

Magnetostriction is the change in the dimensions (length) of a ferromagnetic material when it is magnetized. It is measured by the strain λ=Δl/l\lambda = \Delta l/l, typically 10−610^{-6}–10−510^{-5}.

  • Cause: as domains rotate towards the field, the spin–orbit coupling changes the spacing of atoms along the magnetization direction.
  • Nickel contracts (λ<0\lambda < 0); iron expands at low field.
  H = 0:   |<------- l ------->|
           +-------------------+
           |      Ni rod       |
           +-------------------+

  H on:    |<---- l - dl ---->|
           +------------------+
           |/ / / coil / / / /|   H along the rod
           +------------------+
           lambda = -dl/l  (Ni contracts)

Effects/uses: hum of transformers at 100 Hz; sonar and ultrasonic transducers; sensors (Terfenol-D).

✓ Answer checked by Claude Opus 5.5 (high effort)

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