Magnetism

Outline
• Diamagnetism      W
• Paramagnetism     W
• Brillouin functions
• Ferromagnetism     W
• Curie temperature     W
• Curie-Weiss law     W
• Exchange
• Mean field theory
• Antiferromagnetism     W
• Neel Temperature     W
• Ferrimagnetism     W
• Magnetite      W
• Spinel crystal structure     W
• Magnetic domains     W
• Anisotropy energy
• Hard axis, easy axis
• Bloch walls     W
• Remnant magnetization
• Coersive field
• Hard magnets and soft magnets
• Superparamagnetism     W
• Spin glass     W
• Magnons     W
• Giant magnetoresistance     W
• Magnetoresistive Random Access Memory     W
• Magnetic force microscope      W

Reading
Kittel chapters 11, 12

For the exam you should be able to
• explain why all materials have a diamagnetic response and why the current that flows does not dissipate energy
• explain the form of the paramagnetic susceptibility as a function of temperature for regular paramagnetism and for Pauli paramagnetism
• describe the magnetization of a paramagnetic material as a function of field and temperature (this dependence is given by a Brillouin function)
• explain how the exchange energy is calculated
• plot the magnetization of a ferromagnet, an antiferromagnet, and a ferrimagnet as a function of temperture and magnetic field
• plot the susceptibility of a ferromagnet, an antiferromagnet, and a ferrimagnet as a function of temperature
• give at least one example of a diamagnetic material, a paramagnetic material, a ferromagnetic material, a ferrimagnetic material, an antiferromagnetic material, a hard magnetic material and a soft magnetic material
• define: diamagnetism, paramagnetism, Brillouin function, ferromagnetism, ferrimagnetism, antiferromagnetism, Curie law, Curie-Weiss law, Curie temperature, Neel temperature, Hund's rules, magnetic domains, anisotropy energy, hard magnets, soft magnets, Bloch wall, permeability, remnant field, coercive field, and mean field theory

Student presentations
• Dia-und Paramagnetismus - Hannes Brandner und Nicola Schlatter, 2008
• Magnetismus (ppt) - Bernhard Nell,Alexander Pichler, und David Steffelbauer, 2009
• Ferromagnetismus - Iris Hehn und Martin Nuss, 2009

Resources
• A nice historical overview is given in John H. van Vleck's Nobel lecture. Quantum Mechanics - The Key to Understanding Magnetism, John H. van Vleck, Nobel Prize 1977.
• The Origin, the Development and the Future of Spintronics, Albert Fert, Nobel Prize 2007.
• From Spinwaves to Giant Magnetoresistance (GMR) and Beyond, Peter Grüberg, Nobel Prize 2007.