Neutron scattering study of the incommensurate high-field phase of CuGeO3

CuGeO3 is a good realization of a spin-Peierls system. Using neutron scattering, we have investigated the transition from the dimerized spin-Peierls phase to an incommensurately modulated high-field phase. The incommensurate period has been measured for fields up to 14.5 T and is found to be in excellent accord with the theoretical predictions. The intensities of the satellite reflections provide evidence for the existence of a magnetic contribution with the same modulation period as the structural.

Neutron scattering study of the field-induced soliton lattice in CuGeO3

Mechthild Enderle, Henrik Moodysson Rønnow

CuGeO3 undergoes a transition from a spin-Peierls phase to an incommensurate phase at a critical field of H-c approximate to 12.5 T. In the high-field phase a lattice of solitons forms, with both structural and magnetic components, and these have been studied using neutron scattering techniques. Our results provide direct evidence for a long-ranged magnetic soliton structure which has both staggered and uniform magnetizations with amplitudes that are broadly in accord with theoretical estimates. The magnetic soliton width Gamma(m) and the field dependence of the incommensurability delta k(SP) are found to agree well with theoretical predictions.

2000

The Neutron Scattering Structure Factor

Jérôme Egger

In the experience of neutron scattering, the structure factor is a value that can be almost directly measured (through the differential inelastic neutron scattering cross section). Thus it can be interesting to have a calculation which could give a theoretical point of view, even if the system used in the calculation cannot be as complex as in the real case. Although this calculation (of a simplified system) could be a bad representation of the real system, it is already a point of comparison which yields finally to a better understanding. The present work has the aim to provide a useful matlab code for the computation of the structure factor of small magnetic cluster in “spin-only” scattering. A concrete exemple and the result for a special configuration will be also given.

2010

Long-range magnetic ordering in Li2MnGeO4 and precursor short-range spin correlations

Artem Korshunov, Irina Safiulina

Long-range magnetic ordering and short-range spin correlations in layered noncentrosymmetric orthogermanate Li2MnGeO4 were studied by means of polarized and unpolarized neutron scattering. The combined Rietveld refinement of synchrotron and neutron powder diffraction data at room temperature within the Pmn2(1) space group allowed us to specify the details of the crystal structure. According to the additional Bragg peaks in low-temperature neutron diffraction patterns a long-range antiferromagnetic ordering with the propagation vector k = (1/2 1/2 1/2) has been found below T-N approximate to 8 K. Symmetry analysis revealed the model of the ground state spin structure within the C(a)c (no. 9.41) magnetic space group. It is represented by the noncollinear ordering of manganese atoms with a refined magnetic moment of 4.9 mu(B)/Mn2+ at 1.7 K, which corresponds to the saturated value for the high-spin configuration S = 5/2. Diffuse magnetic scattering was detected on the neutron diffraction patterns at temperatures just above T-N. Its temperature evolution was investigated in detail by polarized neutron scattering with the following XYZ-polarization analysis. Reverse Monte Carlo simulation of diffuse scattering data showed the development of short-range ordering in Li2MnGeO4, which is symmetry consistent on a small scale with the long-range magnetic state below T-N. The reconstructed radial spin-pair correlation function S(0)S(r) displayed the predominant role of antiferromagnetic correlations. It was found that spin correlations are significant only for the nearest magnetic neighbors and almost disappear at r approximate to 12 angstrom at 10 K. Temperature dependence of the diffuse scattering implies short-range ordering long before the magnetic phase transition. Besides, the spin arrangement was found to be similar in both cases above and below T-N. As a result, an exhaustive picture of the gradual formation of magnetic ordering in Li2MnGeO4 is presented.

2020

Long-range magnetic ordering in Li2MnGeO4 and precursor short-range spin correlations

Artem Korshunov, Irina Safiulina

2020