**PH 619** **Magnetism and Magnetic Materials**

1. Introductory magnetism**.**

Review of diamagnetism and paramagnetism; Quantum mechanical treatment of magnetism; Brillouin Function, Curie Law and applications. Pauli paramagnetism.

Wave functions of magnetic ions (3d, 4f); spin-orbit coupling; crystal field effects, Jahn-Teller theorem. Thermodynamics of magnetism, free energy and entropic considerations. Adiabatic demagnetization

2.** **Ferro and Antiferromagnetism**.**

Basic Phenomenon, Mean Field Theory, Thermodynamics of ferromagnetic systems. Quantum mechanical treatment, Exchange interactions, Heisenberg and Ising model. Indirect exchange (superexchange and RKKY). Spin excitations, spin waves, magnons, application to the temperature dependences of magnetization and specific heat. Band ferromagnetism. Criteria for band ferromagnetism; examples of metallic ferromagnets.

__Anti-Ferromagnetism: __Basic phenomenon, Mean Field treatment. Type I**, **Type II Antiferromagnets, Parallel and perpendicular susceptibilities, Spin flop transition. Ferrites, Applications of ferrites.

3. Domain Structures and related properties of ferromagnets

Magnetic Anisotropy, basic phenomenology. Uniaxial, Cubic and surface Anistropies; Effects in bulk materials and thin films. Domain Formation, Domain wall width. Relation to magnetic anisotropy. 900, 1800 domain walls. Observation of domains, Domain wall motion, pinning of domain walls; Magnetization in soft and hard magnets, Magnetization reversal mechanisms, Coherent modes of spin reversal.

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4. Finite size effects

Single Domain Particles and their Magnetic Properties: Anisotropies, Coercive fields and magnetization Stoner- Wohlfarth theory; Superparamagnetism and time decay of magnetization; Neel-Brown models; Exchange bias effects; Dynamic response and applications of single domain particles in magnetic recording. Reversal mechanisms in single domains. Thin films and surface effects.

**Recommended text books:**

*Magnetism in Condensed Matter*, by Stephen Blundell, Oxford Press 2001.-
*Introduction to the theory of Ferromagnetism*by Amikam Aharoni, Oxford Press 1998. -
*Permanent Magnetism*by R.Skomski and J. M. D. Coey, IOP Publishing, 1999. *The Physical Principles of Magnetism*by Allan H. Morrish, John Wiley 1965.-
*Introduction to Solid State Physics*by Charles Kittel, John Wiley 8th Edition.