Module PY3P04 Condensed Matter II
Cohort: JS Physics, JS Physics and Chemistry of Advanced Materials, JS Theoretical Physics
Lecturers: Professors J.M.D. Coey, D. O’Regan
Duration: Hilary Term, Magnetic Properties: 15 lectures, Physics of Semiconductors: 15 lectures
Assesment: End of Year Exam.
Part I: Magnetic Properties: In these lectures we present the quantum theory and properties of paramagnetic ions, treats ferromagnetic order in the molecular field approximation, and provides an introduction to hysteresis and micromagnetism. Topics include: Units in magnetism, spin and orbital moments of the electron, atomic magnetism of single and multi-electron atoms, spin-orbit coupling, Landé g-factor, Zeeman splitting, vector model of the atom. Paramagnetism - classical Langevin theory, quantum theory for S = 1/2 and general spin (Brillouin theory). Curie law. Ferromagnetism-Weiss molecular field theory. Curie temperature, Curie-Weiss law. Origin of ferromagnetism. Heisenberg Hamiltonian. Positive and negative exchange. Demagnetising field. Ferromagnetic domains; hysteresis and coercivity. Magneto-crystalline anisotropy. Stoner-Wohlfarth model. Permanent magnets. Superexchange, molecular field theory of antiferromagnetism. Ferrites. Applications. Analogies with dielectric properties of solids.
Part II: Physics of Semiconductors: Introduction to semiconductors. Charge carrier densities and Fermi level. Intinsic and extrinsic conductivity, doping with impurities. Carrier transport: drift, mobility, diffusion. Motion in magnetic fields: Hall effect and Cyclotron Resonance. Optical processes, optical absorption. Generation and recombination, minority carrier lifetime, photoconductivity. Non-equilibrium transport of charge carriers, the continuity equation. Inhomogeneous doping. The pn junction diode: depletion layer, built-in potential, electric field, current flow. Uses of diodes.