Impurity-induced orthogonal double sinusoidal magnetic structure in the triangular lattice antiferromagnet CuFe 1 − x Al x O 2

摘要: Magnetic ordering has been investigated in detail the low-temperature (LT) phase of triangular lattice antiferromagnet ${\mathrm{CuFe}}_{0.9845}{\mathrm{Al}}_{0.0155}{\mathrm{O}}_{2}$. The LT characterized by original Heisenberg character orbital singlet ${\mathrm{Fe}}^{3+}$ ($S=\frac{5}{2}$, $L=0$) is induced from quasi-Ising four-sublattice $(\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow})$ state ${\mathrm{CuFeO}}_{2}$, a small amount nonmagnetic impurity; nevertheless, magnetic structure was not identified our previous neutron diffraction measurements with triple-axis spectrometer [J. Phys. Soc. Jpn. 74, 2604 (2005)]. In present study, we could determine orthogonal double sinusoidal (ODS) phase, using lifting-counter two-axis diffractometer. ODS consists two spin modulations that are slightly different wave numbers and whose polarization axes to each other. Moreover, keeping determined parameters structure, also discuss stabilization ${\mathrm{CuFeO}}_{2}$.