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magnetic moment vs. electric field @ H=0

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magnetic moment vs. electric field @ H=0

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  1. magnetic moment vs. electric field @ H=0 magnetoelectric coefficient -rhombohedral corundum type structure Cr2O3 moments can order in two different 180° domains -noncentrosymmetric magnetic point group Cr moments have opposite direction with respect to the arrangement of oxygen ligands @T<TN=308K Magnetoelectric effect of Cr2O3 measured by SQUID-magnetometry

  2. @T>0 magn. field creates magnetization Ansatz Origin of the magneto-electric effect  Phenomenological theory, Rado (1961) fictitious field, h, such that ~sublattice magnetization

  3. single ion terms no interaction with neighbors A Cr3+- coordination B  why becomes α negative for T0 ?  what is the microscopic origin of h ? Microscopic view  Hamiltonian of a single Cr3+-Ion in the crystal field E = 0 E = 0 where

  4. A Cr3+,S=3/2 u u B Cr3+ shifted towards A A B shifted towards B O2-  E shifts Cr3+-ions in field direction

  5.  Interaction term exchange interaction where mean field approximation  Interaction term for one ion on place A/B where  electric induced exchange and g-shift seem to dominate in Cr2O3