Dipolar ferromagnets and glasses (invited)

Journal Article · Fri Nov 15 00:00:00 EST 1991 · Journal of Applied Physics; (United States)

DOI:https://doi.org/10.1063/1.350087· OSTI ID:5124617

Rosenbaum, T F; Wu, W; Ellman, B; Yang, J ^[1]; Aeppli, G ^[2]; Reich, D H ^[3]

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1. The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois (USA)
2. AT T Bell Laboratories, Murray Hill, New Jersey (USA)
3. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland (USA)

What is the ground state and what are the dynamics of 10{sup 23} randomly distributed Ising spins We have attempted to answer these questions through magnetic susceptibility, calorimetric, and neutron scattering studies of the randomly diluted dipolar-coupled Ising magnet LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for dipole concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In the dilute spin limit, an {ital x}=0.045 crystal shows very unusual glassy properties characterized by {ital decreasing} barriers to relaxation as {ital T}{r arrow}0. Its properties are consistent with a single low degeneracy ground state with a large gap for excitations. A slightly more concentrated {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample. In addition to tracing the evolution of the glassy and ferromagnetic states with dipole concentration, we investigate the effects of a transverse magnetic field on the Ising spin glass, LiHo{sub 0.167}Y{sub 0.833}F{sub 4}. The transverse field mixes the eigenfunctions of the ground-state Ising doublet with the otherwise inaccessible excited-state levels. We observe a rapid decrease in the characteristic relaxation times, large changes in the spectral form of the relaxation, and a depression of the spin-glass transition temperature with the addition of quantum fluctuations.

• OSTI ID: 5124617
• Journal Information: Journal of Applied Physics; (United States), Vol. 70:10; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HOLMIUM FLUORIDES
GROUND STATES
MAGNETIC PROPERTIES
LITHIUM FLUORIDES
YTTRIUM FLUORIDES
FERROMAGNETIC MATERIALS
ISING MODEL
MAGNETIC MOMENTS
RELAXATION TIME
SPIN GLASS STATE
ALKALI METAL COMPOUNDS
CRYSTAL MODELS
ENERGY LEVELS
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HOLMIUM COMPOUNDS
LITHIUM COMPOUNDS
LITHIUM HALIDES
MAGNETIC MATERIALS
MATERIALS
MATHEMATICAL MODELS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties