Reinvestigation of Magnetic Structures for the Thermally Induced States of CuFe_1-xAl_xO₂(x=0.00, 0.02 and 0.05) Using a Four-Circle Neutron Diffractometer

Abstract

We have reinvestigated the effect of non-magnetic impurity on thermally-induced magnetic orderings in geometrically frustrated triangular lattice antiferromagnets CuFe 1Àx Al x O 2 with x ¼ 0:00, 0.02 and 0.05, using a four-circle neutron diffractometer. Although we inferred in our previous work with a threeaxis diffractometer that a proper screw type magnetic structure is realized in the intermediatetemperature (IM) phase of the samples with x ¼ 0:02 and x ¼ 0:05, in the present work we found that a sinusoidally amplitude-modulated magnetic structure with the magnetic moments canted by about 50 from the c axis toward the hexagonal h1 1 10i direction is realized. These experimental findings suggest that the quasi-Ising magnetic orderings in CuFeO 2 are stabilized not with the strong Ising anisotropy expected from the Ising-like successive magnetic phase transitions in CuFeO 2 but with the small Ising anisotropy added to strongly competing exchange interactions.

Landau analysis of the symmetry of the magnetic structure and magnetoelectric interaction in multiferroics

“…Notice that in this phase, the spins will not lie exactly along the z axis. Indeed, recent work 66 indicates that this phase is one in which the amplitudes are sinusoidally modulated and the spins are oriented in the y-z plane ͑as described by irrep ⌫ 2 ͒ with m y / m z ͑i.e., r / s͒ between 0 and about 0.2.…”

Identification of microscopic spin-polarization coupling in the ferroelectric phase of magnetoelectric multiferroicCuFe1−xAlxO2Nakajima1, Mitsuda2, Inami3 et al. 2008Phys. Rev. BSelf Cite370331View full textAdd to dashboardCite

“…3(c), even though the magnetic structure of the OPD phase does not have threefold rotational symmetry along the c h axis. 24 This suggests that the coherent bond order is not essential to the OPD magnetic ordering. Based on the fact that the OPD phase is never observed without nonmagnetic substitution, it is reasonable to propose that the OPD magnetic ordering is stabilized by local symmetry breaking due to the site-random magnetic vacancies.…”

Ferroelectricity and lattice distortion associated with spin orderings in a multiferroic delafossite AgFeO2

“…Both k-vector and magnetic structure are almost the same as in the intermediate temperature phase of CuFeO 2 . [16,17] The spin direction, however, is significantly different in these compounds, suggesting that the A-site cations play important role determining the magnetic anisotropy of the Fe 3+ spins. Below the second transition at T N2 = 9 K, a cycloidal magnetic structure with propagation vector k = (1 2 q 0.205 1 2 ) and elliptical modulation is stabilized.…”