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The classical, thermally driven transition in the dipolar-coupled Ising ferromagnet LiHoF 4 sTc ­ 1.53 Kd can be converted into a quantum transition driven by a transverse magnetic field Ht at T ­ 0. The transverse field, applied perpendicular to the Ising axis, introduces channels for quantum relaxation, thereby depressing Tc . We have determined the phase(More)
The desire to maximize the sensitivity of read/write heads (and thus the information density) of magnetic storage devices has stimulated interest in the discovery and design of new magnetic materials exhibiting magnetoresistance. Recent discoveries include the 'colossal' magnetoresistance in the manganites and the enhanced magnetoresistance in(More)
Inelastic neutron scattering was used to study the wave vector- and frequency-dependent magnetic fluctuations in single crystals of superconducting YBa2Cu3O6+x. The spectra contain several important features, including a gap in the superconducting state, a pseudogap in the normal state, and the much-discussed resonance peak. The appearance of the pseudogap(More)
There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second description, based on the physics of electron fluids or(More)