SrYb${}_2$O${}_4$  is a geometrically frustrated rare-earth magnet, which presents a variety of interrelated magnetic phenomena. The magnetic Yb${}^{3+}$ ions ($J=7/2$) form potentially frustrated “zigzag” chains along the $c$ axis, arranged in a honeycomb fashion in the $ab$ plane. Heat capacity reveals a magnetic phase transition at $T_{\mathrm{N}}=0.9$ K. The magnetic structure was solved by polarized neutron diffraction and found to be noncollinear with a reduction of the ordered spin moment from the full ionic moment. The low-energy excitations, which were measured by inelastic neutron scattering reveal diffuse scattering both above and below $T_{\mathrm{N}}$. Heat capacity and magnetocaloric effect were performed to map out the magnetic phase diagram as a function of magnetic field and temperature and show a complicated series of states. Altogether, the results suggest that the magnetic interactions in SrYb${}_2$O${}_4$  compete with each other and with the single-ion anisotropy to produce a highly degenerate ground state manifold that suppresses the magnetic order, broadens the excitations and gives rise to a complex phase diagram.

• Received 29 May 2012

DOI:https://doi.org/10.1103/PhysRevB.86.064203