Neutron-Diffraction Determination of the Antiferromagnetic Structure of KCuF3

Abstract

We have investigated the nuclear and magnetic diffraction of neutrons from powder and single-crystal samples of KCuF 3 at temperatures between 298 and 4.4°K, in order to establish the magnetic structure, and, in particular, to try to determine whether there exist any long-range one-dimensional correlations in this material. Previous work has shown that KCuF3 has two stable polytype tetragonal structures which may coexist over a large range of temperatures. The samples used in this work indicated the simultaneous presence of both these structures, and gave diffraction peaks indicative of Du 18 and D^ space groups. Both structures are found to have type-.4 magnetic ordering with the spins lying in the a-b plane. Our results suggest that the D ih 18 structure orders at 38± 1°K, while the D 4h & may order at 22±4°K. The moment of the Cu 2+ ion is determined to be 0.49rfc0.07 /XB. NO direct evidence for one-dimensional order above 38°K nor for long-range one-dimensional correlations has been found, but their presence has not been unambiguously ruled out.

Computation of correlation-induced atomic displacements and structural transformations in paramagneticKCuF3andLaMnO3

“…5,6 While the LDA+U calculations account rather well for the value of equilibrium JT distortion in KCuF 3 , 44 the calculations simultaneously predict long-range antiferromagnetic order which indeed occurs in KCuF 3 below T N (∼ 38 K and 22 K for the a polytype and for the d polytype, respectively). 45 Note, however, that the Néel temperature is much lower than the critical temperature for orbital order which is generally assumed to be as large as the melting temperature (∼ 1000 K). The LDA+U calculations give the correct insulating ground state with the long-range A-type antiferromagnetic and d x 2 −z 2 /d y 2 −z 2 antiferro-orbital order, 6,42,44 consistent with the Goodenough-Kanamori-Anderson rules for a superexchange interaction.…”

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

“…Below the magnetic transition at T N Ӎ 38 K, long-range magnetic order of A type sets in, 50,51 and the ordered moment is 0 = 0.48 B . 52 The superexchange between the Cu 2+ ions in KCuF 3 , Fig. 1͑a͒.…”

Weak ferromagnetism of quasi-one-dimensionalS=12antiferromagnetBaCu2Tsukada1, Takeya2, Masuda3 et al. 2000Phys. Rev. B600191View full textAdd to dashboardCite

“…While in general there are many kinds of magnetic 3D-LRO states, the transition to a normal 3D AF-LRO state has been studied mostly. 2 One remarkable exception is a weak ferromagnetic transition that was recently found in 1D compound Sr 0.73 CuO 2 . 3 However, this compound cannot be treated as a uniform spin-chain system but rather is well explained as an alternating-chain system.…”