Magnetism_F10

Magnetism_F10 - Magnetism GLY 4200 Fall, 2010 1 Early...

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1 Magnetism GLY 4200 Fall, 2010
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2 Early Observations of Magnetism Ancient Greeks, especially those near the city of Magnesia, and Chinese, observed natural stones that attracted iron The naturally magnetic stones are called lodestone The Chinese discovered a steel needle stroked by a lodestone became magnetic, and, if suspended, pointed N-S
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3 What is Magnetism? Although discovered relatively early in man’s history, and exploited, the causes of magnetism were not understood
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4 Orbiting Electrons Moving electrical currents generate magnetic forces This includes electrons orbiting and spinning around a nucleus Each orbiting electron possesses a magnetic moment equal to 1 Bohr magnetron (μB), or 0.927 x 10 -23 Am 2 (Amps meter 2 )
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5 Isolated Ions Net magnetic moment is equal to the sum of: Orbital contributions Spin contributions Filled orbitals give a net contribution of zero to the magnetic moment since the two electrons orbit and spin oppositely
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6 Net Magnetic Moments Generated only in atoms or ions with incomplete electronic shells Most important subshells likely to be incompletely filled are the 3d (first transition row) and the 4f (rare earth elements) The second and third transition rows (4d and 5d electrons) also produce magnetic moments but the elements, and hence the minerals, are rare
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7 Three d Electrons Three d electrons have large spin and relatively low orbital contributions to magnetic moments In compounds the orbital contribution is affected by, and largely negated by, bonding to other ions Since the 4s electrons are outside the 3d, the 3d electrons are partially shielded and the orbital contribution will not be entirely negated
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8 Spin Contribution
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Magnetism_F10 - Magnetism GLY 4200 Fall, 2010 1 Early...

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