Geometrically frustrated magnets - Department of Theoretical Physics

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Magnetism in ionic insulators Many ionic insulators have magnetic ions with an associated magnetic moment due to incomplete shells. Interactions between these localized moments. Magnetic dipolar interaction energy (small ∼ 10 −5 eV). Exchange energy E = J ∑ 〈ij〉 S i · S j due to Coulomb interactions and Pauli exclusion. How big is J? When is it positive? Difficult questions. Arnab Sen, TIFR Geometrically frustrated magnets
Superexchange interaction Consider MnO which is antiferromagnetic ionic solid. Mn 2+ has 5 electrons in its d shell being parallel due to Hund’s rule. O 2− has fully occupied p orbitals. Antiparallel alignment of spins in neighbouring Mn ions has lower kinetic energy due to delocalization of electrons (virtual hoppings). Arnab Sen, TIFR Geometrically frustrated magnets
Page 1: Geometrically frustrated magnets Ar
Page 5 and 6: Frustration Not all the interaction
Page 7 and 8: Schematic of magnetic susceptibilit
Page 9 and 10: Interesting questions Spin liquids
Page 11 and 12: Macroscopic degeneracy II Zero mode
Page 13 and 14: Quantum fluctuations Quantum fluctu
Page 15 and 16: Single-ion anisotropy Motion of the
Page 17 and 18: Zero field To O(J 3 /D 2 ), H eff i
Page 19 and 20: No minority rule H D = 2J 2 ∑P n2
Page 21 and 22: Triangular Lattice Arnab Sen, TIFR
Page 23 and 24: Orientationally ordered state 0 −
Page 25 and 26: Consequences (I) 0 q x π 2 π 2 π
Page 27 and 28: Kagome in magnetic field Include ma
Page 29 and 30: Sublattice symmetry broken a) c) 0
Page 31 and 32: Summary S > 3/2 kagome and triangul

Geometrically frustrated magnets - Department of Theoretical Physics

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