Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets. I. Theory

Abstract

We consider theoretically the effects of an applied uniform magnetic field on the magnetic spectrum of anisotropic two-dimensional and Dzyaloshinskii-Moriya layered quantum Heisenberg antiferromagnets. The former case is relevant for systems such as the two-dimensional square lattice antiferromagnet Sr 2 CuO 2 Cl 2 , while the latter is known to be relevant to the physics of the layered orthorhombic antiferromagnet La 2 CuO 4 . We first establish the correspondence between the low-energy spectrum obtained within the anisotropic nonlinear sigma model and by means of the spin-wave approximation for a standard easy-axis antiferromagnet. Then, we focus on the field-theory approach to calculate the magnetic-field dependence of the magnon gaps and spectral intensities for magnetic fields applied along the three possible crystallographic directions. We discuss the various possible ground states and their evolution with temperature for the different field orientations, and the occurrence of spin-flop transitions for fields perpendicular to the layers ͑transverse fields͒ as well as for fields along the easy axis ͑longitudinal fields͒. Measurements of the one-magnon Raman spectrum in Sr 2 CuO 2 Cl 2 and La 2 CuO 4 and a comparison between the experimental results and the predictions of the present theory will be reported in paper II of this research work ͓L. Benfatto et al., Phys. Rev. B 74, 024416 ͑2006͔͒.

Angle-resolved NMR: Quantitative theory of75AsT1relaxation rate in BaFe2AsSmerald1, Shannon2 2011Phys. Rev. B

“…The low-energy field theory that reproduces the dispersion relation and has all the correct symmetries of the ordered state is 19,25,[28][29][30] …”

Electronic interlayer coupling in the low-temperature tetragonal phase ofLa1.79Eu0.2Sr0.01Hücker1 2009Phys. Rev. B3040View full textAdd to dashboardCite

“…2,8,25,41 Each plane carries a weak ferromagnetic moment ͑WFM͒ which orders antiparallel in adjacent layers for T Ͻ T N . When the external field H ʈ c exceeds the spin-flip field H SF needed to overcome the interlayer coupling J Ќ , the spin lattice of every other layer rotates by = 180°so that the WFMs of all planes become parallel to the field.…”

“…4 La 2 CuO 4 has been an ideal playground for experimental and theoretical studies of interlayer interactions. 2,[5][6][7][8][9] It is amenable to doping and offers examples where a small modification of the crystal structure can change the ground state. Particularly interesting is the case of La 2−x Ba x CuO 4 with x Ӎ 1 / 8, where bulk SC is suppressed and replaced by a static order of charge and spin stripes.…”

ac hopping magnetotransport across the spin-flop transition in lightly dopedLa2CuO4

“…This issue has been recently addressed both experimentally 1-6 and theoretically. [7][8][9] The present work is relevant to La 2−x Sr x CuO 4 , La 2 Cu 1−x Li x O 4 , and La 2 CuO 4+y at very low doping. Generally these compounds have very different properties.…”

“…1,4,5,8,9,28 The spins align completely along ĉ at a field H c2 ϳ 20 T. An intermediate in-plane spin flop is also possible at H c1 Ͻ H c2 . 8,9 The intermediate in-plane spin flop is very sensitive to doping and the situation is different for Sr, Li, and zero doping. 28 However the intermediate in-plane spin flop practically does not influence the transport properties.…”