Soft and Hard Magnetic Materials

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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