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Selection of Magnetic Materials

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Estimated time: 3 minutes
CISCE: Class 12

Permanent Magnets

Property Required: High retentivity + High coercivity

  • Once magnetised, the material must retain magnetism for a long time and must resist demagnetisation by stray external fields.
  • Materials Used: Steel (especially cobalt steel), Alnico, Ticonal.

Steel and its alloys have a wide hysteresis loop, meaning high retentivity and high coercivity — ideal for a stable, long-lasting magnet.

Real-life Example: Loudspeaker magnets and magnetic compass needles use alnico/steel because they must stay magnetised indefinitely without an external field.

CISCE: Class 12

Electromagnets

Property Required: High permeability (especially at low magnetising fields) + Low retentivity

  • Must magnetise easily when current flows and demagnetise quickly when current stops — needed for switching applications.
  • Material Used: Soft iron.

Soft iron has a narrow hysteresis loop — it gains and loses magnetism rapidly with minimal energy loss, and does not retain magnetism once the current is switched off.

Real-life Example: Electric bell mechanisms and cranes that lift/drop scrap metal rely on soft iron cores that lose magnetism instantly when power is cut.

CISCE: Class 12

Transformer Cores & Telephone Diaphragms

Property Required: Low hysteresis loss + High permeability + High specific resistance

  • The core must minimise energy dissipation (heat loss) and eddy-current losses during continuous AC cycling.
  • Materials Used: Soft iron, Permalloy, Mu-metal.

These alloys combine very low hysteresis loss with high electrical resistance, reducing both hysteresis and eddy-current heating — crucial for devices operating continuously on an AC supply.

Real-life Example: Transformer laminated cores use silicon steel/permalloy to minimise energy loss during 24/7 operation in power grids.

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