Motivating ESM2009 Why do we like magnetism? Why do we need models? - PowerPoint PPT Presentation

Motivating ESM2009 Why do we like magnetism? Why do we need models? Peter de Châtel Institute of Nuclear Research Hungarian Academy of Sciences Debrecen, Hungary

Why do we like magnetism? It is fascinating (“on s’amuse”) We have witnessed two recent breakthroughs, which inspire our sponsors: 1. Lighter, stronger and more stable magnets 2. GMR hit the market at an unprecedented speed

2. GMR hit the market at an unprecedented speed     

Nobel prize physics 2007 Giant magneto resistance Albert Fert Peter Grünberg

Why do we need models? Why models, rather than the Real Thing? Microscopic level: relativistic and quantum- mechanical (Bohr - van Leeuwen theorem) Phenomenalogical level: nonlinear and irreversible (hysteresis)

Magnetic field, Spin and orbital magnetic moments, Crystal electric field John Michael Coey Today, Monday 01/09 14h

Mean field theory Claudine Lacroix Friday 04/09 14h

The four bilinear model interactions , .     H 2 J S S Heisenberg Heis ij i j  i j  y y x x    H 2 J ( S S S S ); XY XY ij i j i j  i j  z z Ising   H 2 J S S . Is ij i l  i j Dzyaloshinskii     H d ( S S ) DM ij i j Moriya  i j

Thursday 03/09 11h

Monte Carlo methods for magnetic systems Zoltán Néda Sunday 06/09 15h

Direct exchange Parallel-spin electrons do not come too close to each other, that saves some Coulomb energy. Consequently, a given number of electrons claims a larger volume, if the spins are aligned.

Superexchange , Delocalization is realized by hopping onto a neighbouring site, t is the hopping matrix element t      an an d  E E an d 2 t    E  E E an d

Wednesday 04/09 10h30 and 14h30

Free electrons in a magnetic field (external or molecular) The Zeeman energy modifies the spectrum of available states, a rearrangement of occupancies occurs. In the new equilibrium state there is a net spin momentum and magnetisation. S.V. Vonsovskii, Magnetism Vol.1 (1974)

Magnetism of free electrons J.M.D. Coey Thursday 03/09 9h

Density of states in cobalt and iron Co Fe E.Yu. Tsymbal and D.G. Pettifor Phys. Rev. B 54 (1996) 15314

Basics of electronic structure calculations for magnetic systems: Tight binding, LDA, DMFT Manual Richter Tuesday 01/09 16h and Thursday 04/09 11h

Spin wave in an antiferromagnet in an external field H 0

Wulf Wulfhekel Monday 07/09 12h

Magnetic anisotropy and how it can be controlled Dirk Sander Thursday 03/09 12h

Review of typical behaviours observed in strongly correlated systems Charles Simon Saturday 05/09 11h

Spin fluctuation theory for itinerant magnetism and introduction to The physics of the Kondo effect Mireille Lavagna Friday 04/09 16h and Saturday 05/09 9h

Metal-insulator transition ( Mott-Hubbard ) and Magnetism and superconductivity Jozef Spałek Saturday 05/09 14h30 and Sunday 06/09 9h

Models in spin electronics Bernard Diény Tuesday 08/09 14h and Thursday 10/09 10h30

Magnetisation dynamics at different timescales: dissipation and thermal processes Oksana Chubykalo-Fesenko Sunday 06/09 11h and Monday 07/09 11h

Simple concepts of magnetisation reversal from materials to nanostructures Olivier Fruchart Monday 07/09 9h, Tuesday 08/09 16h and Thursday 10/09 16h

Preisach model of hysteresis in magnetic materials and FORC* based identification techniques Alexandru Stancu Thursday 10/9 9h FORC: First-order Reversal Curves

Transport in magnetic semiconductors Tomasz Dietl Wednesday 09/09/09 14h

Amusez-vous bien

Molecular field in the Heisenberg mode l     H 2 J S S Heis ij i j  i j       g S B 2 S J S B i mf i ij j j      H g S ( B B ) mf B i mf i

Nobel prize physics 2007 Giant magnetoresistance Peter Grünberg Albert Fert