0000000000010772
AUTHOR
Jan-willem G. Bos
Spin-chain correlations in the frustrated triangular lattice material CuMnO$_2$
The Ising triangular lattice remains the classic test-case for frustrated magnetism. Here we report neutron scattering measurements of short range magnetic order in CuMnO$_2$, which consists of a distorted lattice of Mn$^{3+}$ spins with single-ion anisotropy. Physical property measurements on CuMnO$_2$ are consistent with 1D correlations caused by anisotropic orbital occupation. However the diffuse magnetic neutron scattering seen in powder measurements has previously been fitted by 2D Warren-type correlations. Using neutron spectroscopy, we show that paramagnetic fluctuations persist up to $\sim$25 meV above TN= 65 K. This is comparable to the incident energy of typical diffractometers, a…
Decoupling lattice and magnetic instabilities in frustrated CuMnO$_2$
The $A$MnO$_{2}$ delafossites ($A$=Na, Cu), are model frustrated antiferromagnets, with triangular layers of Mn$^{3+}$~spins. At low temperatures ($T_{N}$=65 K), a $C2/m \rightarrow P\overline{1}$ transition is found in CuMnO$_2$, which breaks frustration and establishes magnetic order. In contrast to this clean transition, $A$=Na only shows short-range distortions at $T_N$. Here we report a systematic crystallographic, spectroscopic, and theoretical investigation of CuMnO$_2$. We show that, even in stoichiometric samples, non-zero anisotropic Cu displacements co-exist with magnetic order. Using X-ray/neutron diffraction and Raman scattering, we show that high pressures acts to decouple the…