Discussion
The magnetization (M) - magnetic field (H) curves for four different materials are given below. Which one of these materials is most suitable for use as a permanent magnet?
- A.
- B.
- C.
- D.
Answer: C
The material best suited to a permanent magnet is (C).
A permanent magnet must keep a large magnetization when the field is removed (high remanence, where the loop crosses the M axis) and must resist being demagnetized (high coercivity, where it crosses the H axis). Such hard magnetic materials have broad, square loops enclosing a large area.
Loop (C) is the widest, crossing the H axis at about 2.5 units, and also the tallest, so it has both the largest coercivity and the largest remanence. Loops (A), (B) and (D) are progressively narrower: a few tenths to just over one unit of field would demagnetize them. Narrow loops suit soft magnetic materials, such as transformer cores, where low hysteresis loss matters.
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