Collaborators A simple frustrated magnet: La4Cu3MoO12 SrCr9pGa12-9pO19 : Kagome’ s in addition to wich Fe & Cr Jarosite: coupled Kagome’ layers ZnCr2O4 : Corner sharing tetrahedra

Collaborators A simple frustrated magnet: La4Cu3MoO12 SrCr9pGa12-9pO19 : Kagome’ s in addition to wich Fe & Cr Jarosite: coupled Kagome’ layers ZnCr2O4 : Corner sharing tetrahedra www.phwiki.com

Collaborators A simple frustrated magnet: La4Cu3MoO12 SrCr9pGa12-9pO19 : Kagome’ s in addition to wich Fe & Cr Jarosite: coupled Kagome’ layers ZnCr2O4 : Corner sharing tetrahedra

Oehler, Jody, Host has reference to this Academic Journal, PHwiki organized this Journal Neutron Scattering of Frustrated Antiferromagnets Satisfaction without LRO Paramagnetic phase Low Temperature phase Spin glass phase Long range order Spin Peierls like phase Conclusions Collin Broholm Johns Hopkins University in addition to NIST Center as long as Neutron Research Supported by the NSF through DMR-9453362 in addition to DMR-0074571 SrCr9pGa12-9pO19 KCr3(OD)6(SO4)2 ZnCr2O4 Collaborators S.-H. Lee NIST in addition to University of MD M. Adams ISIS Facility, RAL G. Aeppli NEC Research Institute E. Bucher University of Konstanz C. J. Carlile ISIS Facility, RAL S.-W. Cheong Bell Labs in addition to Rutgers Univ. M. F. Collins McMaster University R. W. Erwin NIST L. Heller McMaster University B. Hessen Bell Labs/Shell T. J. L. Jones ISIS Facility, RAL T. H. Kim Rutgers University C. Kloc Bell Labs N. Lacevic Johns Hopkins University T. G. Perring ISIS Facility, RAL A. P. Ramirez Bell Labs W. Ratcliff III Rutgers University A. Taylor ISIS Facility, RAL A simple frustrated magnet: La4Cu3MoO12 Masaki Azuma et al. (2000)

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Magnetization in addition to order of composite trimer spins Theory of spins with AFM interactions on corner-sharing tetrahedra What is special about this lattice in addition to this spin system Low coordination number Triangular motif Infinite set of mean field ground states with zero net spin on all tetrahedra No barriers between mean field ground states Q-space degeneracy as long as spin waves SrCr9pGa12-9pO19 : Kagome’ s in addition to wich Isolated spin dimer Kagome’-Triangular-Kagome’ s in addition to wich (111) slab of pyrochlore/spinel AFM A. P. Ramirez et al. PRL (1990)

Fe & Cr Jarosite: coupled Kagome’ layers A. S. Wills et al. (2000) AM3(OH)6(SO4)2 Townsend et al (1986) Lee et al. (1997) KCr3(OH)6(CrO4)2 ZnCr2O4 : Corner sharing tetrahedra Magnetic Neutron Scattering The scattering cross section is proportional to the Fourier trans as long as med dynamic spin correlation function Fluctuation dissipation theorem:

NIST Center as long as Neutron Research Detection system on SPINS neutron spectrometer

Spatial correlation length saturates as long as T 0 SrCr9pGa12-9pO19 as long as T90% Cr 75-90% Cr

Weak order / strong fluctuations Impurity enhanced LRO in (DO3)Fe3-xAly(SO4)2(OD)6 Wills et al (1998) Wills et al. (2000) DIntensity (arb) 100% Fe 89% Fe Only reported Jarosite w/o LRO Diamagnetic impurities yield LRO Magneto-elastic effects in frustrated AFM Can magneto-elastic coupling relieve frustration What is magnetic in addition to lattice strain configuration in ordered phase Determine energetics of a spin-Peierls like transition as long as frustrated magnets. What are excitations from the ordered phase

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First order phase transition in ZnCr2O4 Dynamics: Low energy paramag. Fluctuations as long as m a resonance at 4.5 meV Statics: Staggered magnetization tetragonal lattice distortion Local spin resonance in ordered phase Paramagnetic fluctuations in frustrated AFM Local spin resonance in magneto-elastic LRO phase Low T excitations in ZnCr2O4: Magnetic DOS Q-dep. of E-integ. intensity C A A: Bragg peaks B: Spin waves C: Resonance D: Upper b in addition to

Spectra at specific Q Dispersion relation as long as resonance ZnCr2O4 single crystals T=1.5 K Structure factor as long as resonance ZnCr2O4 T=1.4 K

Conclusions Low connectivity in addition to triangular motif yields cooperative paramagnet as long as T/QCW 1. The paramagnet consists of small spin clusters with no net moment, which fluctuate at a rate of order kBT/ h. Spinels can have entropy driven magneto-elastic transition to Neel order with spin-Peirls analogies. The ordered phase has a spin-resonance, as expected as long as under-constrained in addition to weakly connected systems. Pyrochlore’s can have a soft mode transition to a spin-glass even when there is little or no quenched disorder. Variations of sub-leading interactions in pyrochlore’s give different types of SRO in different compounds. Lattice distortions may be a common route to relieving frustration in addition to lowering the free energy of geometrically frustrated magnets. Tetragonal ZnCr2O4 Y2Mo2O7

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