Highly frustrated magnetism in SrHo2O4: Coexistence of two types of short-range order

SrHo2O4 is a geometrically frustrated magnet in which the magnetic Ho3+ ions form honeycomb layers connected through a network of zigzag chains. At low-temperature two distinct types of short-range magnetic order can be inferred from single-crystal diffraction data, collected using both polarized and unpolarized neutrons. In the (hk0) plane the diffuse scattering is most noticeable around the k = 0 positions and its intensity rapidly increases at temperatures below 0.7 K. In addition, planes of diffuse scattering at Q = (hk +/- l/2) are visible at temperatures as high as 4.5 K. These planes coexist with the broad peaks of diffuse scattering in the (hk0) plane at low temperatures. Correlation lengths associated with the broad peaks are L approximate to 150 angstrom in the a-b plane and L approximate to 190 angstrom along the c axis, while the correlation length associated with the diffuse scattering planes is L approximate to 230 angstrom along the c axis at the lowest temperature. Both types of diffuse scattering are elastic in nature. The highly unusual coexistence of the two types of diffuse scattering in SrHo2O4 is likely to be the result of the presence of two crystallographically inequivalent sites for Ho3+ in the unit cell.