Magnetic field tuning of quantum spin excitations in a weakly coupled S=12 Heisenberg spin chain as seen from NMR

Abstract

We report our NMR study of the spin excitations in the quasi-one dimensional (1D) S = 1/2 quantum magnet CH3NH3Cu(HCOO)3 lying in the 1D-3D dimensional crossover regime with Dzyaloshinskii-Moriya(DM) interactions. Above TN , the spinon excitation is observed from the constant 1/T1 at low temperatures contributed from the staggered spin susceptibility. At low temperatures well below TN , the 1/T1 begins to flatten out under weak magnetic fields. With the increasing field intensity, 1/T1 tends to show a power-law temperature dependence gradually, with the index increasing from zero to ∼ 3, and finally ∼ 5, which are the respective typical characteristic for the dominating two-magnon Raman process and three-magnon scattering contributions to the nuclear relaxation in a conventional 3D magnet. A possible physical mechanism for this novel magnetic field tuning of quantum spin excitations related with the enhanced effective staggered field created by the DM interactions under magnetic field is discussed.

Defect-induced ferromagnetism in a S = 1/2 quasi-one-dimensional Heisenberg antiferromagnetic chain compound

“…The susceptibility in both directions is almost identical above 4 K, but the value of susceptibility for H perpendicular to b axis is almost twenty times than that of H parallel to b axis at 2 K, which is unusual for an antiferromagnet. From the previous study 9 , the spin canting is proposed from the spectral analysis. Such specific magnetic moments configurations can account for the measured strong anisotropic susceptibility.…”

Defect-induced ferromagnetism in a S=1/2 quasi-one-dimensional Heisenberg antiferromagnetic chain compound

“…The susceptibility in both directions is almost identical above 4 K, but the value of susceptibility for H perpendicular to b axis is almost twenty times than that of H parallel to b axis at 2 K, which is unusual for an antiferromagnet. From previous studies [9], the spin canting is proposed from the spectral analysis. Such specific magnetic moments configurations can account for the measured strong anisotropic susceptibility.…”