Magnetism in the reentrant superconductor ErRh4B4 has been studied by neutron scattering as a function of an applied magnetic field. For a temperature of 1.69 K long-range ferromagnetism is found in fields higher than 1 kOe. Considerable hysteresis is found in the neutron scattering intensity vs magnetic field curve and long-range order with a small Er moment remains when the field is reduced to small values. © 1980, All rights reserved.

Magnetic susceptibility, specific heat, and resistivity measurements by Fisk et al. have revealed two ordering transitions in HoB4 at temperatures near 7.1 and 5.7 K. Moreover, the macroscopic measurements indicate that the higher temperature transition is of second order, the lower one of first order. Neutron diffraction measurements on polycrystalline and on single crystal specimens have confirmed these results. The magnetic scattering data have so far resisted a complete interpretation; the following conclusions can, however, be drawn. The magnetic structure in the high temperature phase has a strong oscillatory component, the wave vector of which is equal to (±0.021,±0.021, 0.425) in units of the reciprocal lattice vectors. The magnetic moments are parallel, in sheets normal to the tetragonal c-axis, to one of the four equivalent [100] reciprocal lattice directions. In the low-temperature phase there is a large component of the moments arranged in the simple colinear structure that has been reported for ErB4 and DyB4 by W. Schafer et al. In both temperature ranges there are additional, unexplained, magnetically scattered intensities. The magnetic phase diagram has been studied in applied fields up to 6.4 T and at temperatures down to 1.8 K. Polarization analysis and classical polarized beam techniques have been applied to the single crystals in selected field and temperature ranges.

Neutron-diffraction measurements have been taken on single crystals of NdBa2Cu3O6+x to explore the nature of the magnetic order as a function of oxygen concentration x. The Cu-O planes are known to order antiferromagnetically at TN1, with TN1(x0) 450 K. At lower temperatures we find that the oxygen-deficient Cu planes also order magnetically [TN2(x0.1) 80 K], with a large ordered moment of 0.46B and a simple antiferromagnetic sequencing along the c axis. Both ordering temperatures decrease with increasing x, with TN2 being much more sensitive to x than TN1. © 1988 The American Physical Society.

Using neutron scattering techniques we have examined the magnetic transitions for compounds in the (Ho1-xErx)Rh4B4 pseudoternary system. We find a wide variety of behavior ranging from mean-field behavior for HoRh4B4 to complicated behavior with more than one type of ordering for Ho0.3Er0.7Rh4B4. Our results for the pseudoternary compounds are consistent with a model in which Ho orders along the c axis with nearly its free-ion moment, while ER orders in the basal plane, but with a moment reduced from the free-ion value. Ordering along the c axis results in the destruction of superconductivity in a sharp transition at the same temperature that a sharp spike appears in the heat capacity. Because Ho and Er have competing orthogonal magnetic anisotropies, pseudoternary compounds near the composition Ho0.3Er0.7Rh4B4 are near a multicritical point in the magnetic phase diagram. © 1982 The American Physical Society.

We have employed polarized and unpolarized neutron-diffraction techniques on both powders and single crystals to establish the nature of the magnetic order of the Cu ions in oxygen-deficient (nonsuperconducting) RBa2Cu3O6+x (R=Y,Nd). Magnetic Bragg peaks of the type (h2,k2,l) are observed that yield a magnetic structure in which the Cu spins are coupled antiferromagnetically both in the Cu-O planes as well as along the tetragonal c axis, with the spin direction in the tetragonal plane. The Néel temperature is very sensitive to the oxygen content, with TN(x1/40)500 K, while the spin configuration is independent of x. © 1988 The American Physical Society.

The magnetic dynamics of La2CuO4 have been studied by means of inelastic neutron scattering in the energy range 0Latin small letter h with stroke140 meV. Experiments were carried out using a wide range of incident neutron energies so as to optimize the experimental resolution in each energy range studied. For energy transfers, Latin small letter h with stroke10 meV, and temperatures T in the range 5T320 K, we find that conventional spin-wave theory gives a good description of the magnetic dynamics. We obtain a low-temperature spin-wave velocity Latin small letter h with strokec=85030 meV. For low energies, Latin small letter h with stroke10 meV, and temperatures corresponding to the paramagnetic phase, our data indicate a response function consisting of overdamped spin waves and a quasielastic peak. © 1990 The American Physical Society.

The results of neutron-diffraction measurements are reported which confirm the development of long-range magnetic order in superconducting NdRh4B4. Two distinct antiferromagnetic transitions occur below the superconducting phase-transition temperature TSC=5.4 K, one at TMH 1.5 K and the other at TML 1.0 K. In both phases, the body-centered tetragonal sublattice of Nd atoms orders antiferromagnetically with the Nd3+ moments aligned along the unique c axis. The magnetic moment is modulated sinusoidally along the [100] direction in the higher-temperature magnetic phase and along the [110] direction in the lower-temperature phase. The measured saturation moment is 3.4± 0.5μB. No ferromagnetic component could be detected in the higher-temperature magnetic phase within an experimental sensitivity of 0.3μB. © 1982 The American Physical Society.

We have used high energy inelastic neutron scattering to study the magnetic fluctuation spectrum of La2CuO4 in the energy and momentum ranges 30≤h{stroke};σ≤140 meV and |q|≤0.2 Å-1, respectively. Our results are consistent, within the experimental error, with conventional spin wave theory the low temperature spin wave velocity, being 850±30 meV Å-1. © 1990.

The results of recent inelastic neutron scattering investigations of the magnetic excitations in La2CuO4 are reviewed. Experiments were performed using a wide range of incident neutron energies. Our study of the paramagnetic phase is consistent with a picture for the magnetic dynamics which shows conventional spin waves at higher energies and an overdamped response due to spin wave interactions at lower energies. The evolution of the magnetic dynamics with doping in the La2-x(Ba, Sr)xCuO4 system is discussed. © 1991, American Institute of Physics. All rights reserved.