Magnetization, specific heat, and neutron scattering measurements were performed to study a magnetic transition in jarosite, a spin-$\frac{5}{2}$ kagome lattice antiferromagnet. When a magnetic field is applied perpendicular to the kagome plane, magnetizations in the ordered state show a sudden increase at a critical field $H_c$, indicative of the transition from antiferromagnetic to ferromagnetic states. This sudden increase arises as the spins on alternate kagome planes rotate ${180}^{°}$ to ferromagnetically align the canted moments along the field direction. The canted moment on a single kagome plane is a result of the Dzyaloshinskii-Moriya interaction. For $H<H_c$, the weak ferromagnetic interlayer coupling forces the spins to align in such an arrangement that the canted components on any two adjacent layers are equal and opposite, yielding a zero net magnetic moment. For $H>H_c$, the Zeeman energy overcomes the interlayer coupling causing the spins on the alternate layers to rotate, aligning the canted moments along the field direction. Neutron scattering measurements provide the first direct evidence of this ${180}^{°}$ spin rotation at the transition.

• Received 1 February 2011

DOI:https://doi.org/10.1103/PhysRevB.83.214406