Correlation between weak ferromagnetism and crystal symmetry inGd2CuO4-type cuprates

Abstract

Correlation between copper weak ferromagnetism ͑WF͒ and crystal structural symmetry of the Gd 2Ϫx M x CuO 4 ͑M ϭBi or Tb; 0рxр0.5͒ systems is reported. Detailed powder x-ray Rietveld refinement analysis on Gd 2Ϫx M x CuO 4 shows a systematic variation of oxygen distortion angle ␣͑Cu-O-Cu͒ with ionic size where the lattice layer mismatch lowers the crystal symmetry to an orthorhombic OЈ-phase with pseudotetragonal lattice parameter a 0 ϳb 0 ϳ5.508 Å. Weak ferromagnetic or canted antiferromagnetic order is the direct result of this oxygen distortion which causes a -transfer Cu(3d x 2 Ϫy 2) -O(2p )-Cu(3d x 2 Ϫy 2) superexchange interaction in the CuO 2 plane with a non-180°coupling angle. The small WF saturation moment m s of ϳ2 -6ϫ10 Ϫ2 B /Cu 2ϩ can be deduced from the copper moment ͑Cu 2ϩ ͒ canting angle ϭ(Ϫ␣)/2 ϳ2 -7°. Magnetic data and internal exchange field B int estimation indicate that Cu 2ϩ WF saturation moment m s ͑Cu 2ϩ ͒ decreases with larger Bi 3ϩ doping and increases with smaller Tb 3ϩ doping.

Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets

“…where w D (n) is determined by (5) or (6). The energy ( 8) and ( 7) were derived from (3) by ignoring the paraprocess and assuming weak total magnetization, |m| ≪ 1, implying |l| ≃ 1.…”

“…It influences appreciably the magnetic properties of several important classes of magnetic materials such as orthoferrites, manganites, some hightemperature superconducting cuprates, and others. 4,6 Another fundamental macroscopic manifestation of antisymmetric couplings (1) takes place in noncentrosymmetric magnetic crystals. Dzyaloshinskii showed that, in this case, the interaction (1) stabilizes long-periodic spatially modulated structures with fixed sense of rotation of the vectors S i .…”

“…The energy contributions (5) and (6) can result in states with modulations in the basal tetragonal plane, i.e. with a propagation vector in the XOY -plane.…”

Measuring interfacial Dzyaloshinskii-Moriya interaction in ultra-thin magnetic films

“…The DMI was first proposed in the 1950's for antiferromagnets such as α-Fe 2 O 3 to account for the existence of a weak ferromagnetism (Dzyaloshinskii, 1957;Moriya, 1960). In the following decades, several magnetic materials, such as spin glasses, orthoferrites, manganites or superconducting cuprates (Bogdanov et al, 2002;Coffey et al, 1991;Fert and Levy, 1980;Luo et al, 1999), were investigated for their noncollinear or helical magnetism and for the influence of DMI on the magnetic state. Theoretical models in non-collinear magnetism are often based on ab-initio calculations and density functional theory (Sandratskii, 1998).…”

Weak ferromagnetism with very large canting in a chiral lattice:Fe(pyrimidine)2Cl2Feyerherm1, Loose2, Ishida3 et al. 2004Phys. Rev. B410220View full textAdd to dashboardCite

“…For these materials, a correlation between weak ferromagnetism and the crystal symmetry has been discussed in detail. 30 We believe that such a correlation is also present in PFC and that the large canting observed in this compound is a direct result of its chiral lattice symmetry. Due to this symmetry, the orientation of the local easy axis varies by 90…”