Soft and Hard Magnetic Materials

Material Science

Soft Magnetic Materials

  • These materials are easy to magnetise and demagnetise.
  • These materials favour rapid switching (it means high frequency) of magnetism to applied ac field.
  • These materials have low retentivity.
  • Low coercivity.
  • High permeability
  • High magnetic saturation
  • Low hysteresis losses because of the lesser area of the hysteresis loop.
  • These materials are used for transformer and inductances core to minimize energy dissipation (reduction in hysteresis area).
  • Desirable for electromagnets.

Examples

1. Si-Steel/ Soft iron/ Fe-Si alloy

  • It is used up to power frequency (50 to 60 Hz).
  • It is used in power transformer.
  • When 5% Si is added, it increases maximum permissible d.c. resistivity and reduces the area of hysteresis loop (low hysteresis losses).
  • low eddy current losses.

2. Fe-Ni alloy

  1. 36% Ni (Invar): It is used for a high-frequency application such are used as high-speed relay and transformer.
  2. 50% Ni: It is used for magnetic memory.
  3. 77% Ni: It is used for precision voltage and current transformer.
  4. Permalloy: have 45% Ni
  5. Super-alloy: have 79% Ni
  6. Mu-metal: have 75% Ni

Note: (iv), (v) and (vi) have high permeability and less area of the hysteresis loop.

Hard Magnetic Materials

  • These materials are also called permanent magnet material.
  • These materials retain their magnetisation and difficult to demagnetise.
  • These materials have high retentivity.
  • High Coercivity
  • High permeability
  • High magnetic saturation
  • High Curie point or temperature
  • High hysteresis losses because of the larger area of the hysteresis loop.

Examples

  1. Carbon steel: It is used as a magnet for latching relays or compass needle.
  2. Tungeston steel: It is used as magnets in D.C. motors.
  3. AlNiCo (Al, Ni, Co): There magnetic properties are very stable with time and temperature.
  4. Ba-ferrite
  5. Remalloy
  6. Cunite (Cu, Ni, Co)

Difference between Soft and Hard Magnetic Materials

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