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GLG 201 4.11.07 - contains remanent magnetization Three...

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Types of Magnetic Behavior Paramagnetism Diamagnetism Ferromagnetism Almost all materials fall in to one of these categories, and materials can switch categories under different conditions, particularly changes in temperature Paramagnetism: Weak Materials acquire a magnetization PARALLEL to the applied field AND Magnetization goes to ZERO when field is removed Diamagnetism: Weak Magnetization in anti-parallel to field Goes to zero when field is removed Ferromagnetism: Strong (1000x) Atomic magnetic moments COUPLE Produces STRONG magnetization PERMANENT under certain conditions Actually, different types of ferromagnetism For GLG 201, just one type Remanent Magnetization: a rock is recording an ancient field If a rock contains minerals that record Earth’s magnetic field at some time in the past, then it
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Unformatted text preview: contains remanent magnetization Three types: 1. Thermoremanence (basalt, granite) At high tempertature, ferromagnetic minerals are paramagnetic Material cools, minerals become ferromagnetic Acquire a magnetization PARALLEL to Earth’s field Currie Temp: temp at which paramagnetic becomes ferromagnetic 580 c for magnetite 680 c for hematite 2. Chemical remanence 3. Detrital remanence Properties of modern geomagnetic field 90% of field can be modeled with a DIPOLE (bar magnet) 10% of field is non-dipole Field Intensity changes over time Intensity is correlated with polarity reversals Expect field to get weaker just before polarity change And, expect to see more field that CAN’T be modeled by dipole Exactly what we see today…...
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GLG 201 4.11.07 - contains remanent magnetization Three...

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