Physics · Ch 11 — Magnetic Materials

Magnetic Properties of Materials

11.5

Magnetic Properties of Materials

Every material's magnetic behaviour, once an external field is applied, can be classified broadly into one of three categories based purely on the sign and typical magnitude of its susceptibility $\chi$ : diamagnetic materials have a small, NEGATIVE $\chi$ ; paramagnetic materials have a small, POSITIVE $\chi$ ; and ferromagnetic materials have a LARGE, positive $\chi$ (often $10^2$ to $10^3$ , many orders of magnitude bigger than a typical paramagnetic value). Table 11.1 lists representative diamagnetic and paramagnetic substances with their measured $\chi$ values, and Table 11.2 summarises the characteristic range of $\chi$ for all three categories -- together, they set the scale for the three det …

Table T1Table 11.1: Magnetic susceptibility of some materials

Diamagnetic substance | $\chi$ | Paramagnetic substance | $\chi$

Silicon | $-4.2\times10^{-6}$ | Aluminium | $2.3\times10^{-5}$

Bismuth | $-1.66\times10^{-5}$ | Calcium | $1.9\times10^{-5}$

Copper | $-9.8\times10^{-6}$ | Chromium | $2.7\times10^{-4}$

Diamond | $-2.2\times10^{-5}$ | Lithium | $2.1\times10^{-5}$

Gold | $-3.6\times10^{-5}$ | Magnesium | $1.2\times10^{-5}$

Lead | $-1.7\times10^{-5}$ | Niobium | $2.6\times10^{-5}$ …

Table T2Table 11.2: Range of magnetic susceptibility of diamagnetic, paramagnetic and ferromagnetic materials

Type of material | Range of $\chi$

Diamagnetic | $-10^{-3}$ to $-10^{-5}$

Paramagnetic | 0 to $10^{-3}$

Ferromagnetic | $10^2$ to $10^3$

This table summarises, at a glance, the huge jump in scale between paramagnetic materials (where $\chi$ never exceeds about $10^{-3}$ ) and ferromagnetic materials (where $\chi$ can be a hundred to a thousand times larger still), which is exactly why only ferromagnetic materials can be …

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