Magnetic ground state of the frustrated spin- 12 chain compound β–TeVO4 at high magnetic fields

Abstract

Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW) and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of β-TeVO4, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at ∼3 T for the magnetic field along the a and c crystal axes, and at ∼9 T for the field along the b axis. The high-field (HF) state, existing above ∼18 T, i.e., above ∼1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin nematic phase in β-TeVO4 is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.

Magnetic-field-induced reorientation in the spin-density-wave and the spin-stripe phases of the frustrated spin- 12 chain compound β−TeVO4

“…For µ 0 H = 2 and 3 T there is a small increase observed in θ 2 at T ≈ 2.2 K marked by the arrow in Fig. 4(a) at T N3 which is absent for µ 0 H = 4 and 5 T. This small change in θ 2 was noticed previously in the torque measurements in low field 14 and it signifies a phase transition form the spin-stripe phase to the VC phase, which does not occur for µ 0 H ≥ 4 T in the ac plane 15,16,19,24 . Interestingly, this increase is absent for θ 1 for all applied fields ( Fig.…”

“…The phase transition temperature T N1 ≈ 4.6 K from the SDW to the spin-stripe phase does not change significantly with the field magnitude or direction 15,16,24 . We established from our curves measured at T = 5 K and T = 4.2 K in both planes, that at the former temperature the system is in the PM state [curves can be fitted to Eqs.…”

“…The magnetic phase diagram of β-TeVO 4 is highly complex 15,16,19,24 . Taking into account all the previous results as well as the results obtained in this work (Fig.…”

“…2 and 3. There are two possible reasons for this deviation: (1) the phase diagram of β-TeVO 4 is highly anisotropic 15,16,24 , so we are probing different magnetic phases at different temperatures, magnitudes and directions of the magnetic field, or (2) the rotation of constant magnetic field at constant temperature is changing the magnetic structure within the particular magnetic phase (spin reorientation phenomenon). Regarding the feature (1), here we jump ahead and color the data points in Figs.…”

“…The spin-density-wave (SDW) phase with the collinear incommensurate amplitude-modulated magnetic order (T N2 < T < T N1 ) is followed by a dynamic spin-stripe phase (T N3 < T < T N2 ) that still has a SDW character, and finally by a vector chiral (VC) phase, which has an elliptical-spiral magnetic order (T < T N3 ) 19 . Phase boundaries depend not only on the magnitude of the magnetic field, but also on the field direction 15,16,24 , which hints to an important role of magnetic anisotropy 25 . Furthermore, the spin-stripe phase was recently proposed to host a new type of elementary excitation named "wigglon" which represents a bound state of two orthogonally polarized phason quasiparticles where higher-order magnetic anisotropies play a vital role 17 .…”