We present the investigation of a monoclinic compound SeCuO 3 using x-ray powder diffraction, magnetization, torque, and electron-spin-resonance. Structurally based analysis suggests that SeCuO 3 can be considered as a three-dimensional network of tetramers. The values of intratetramer exchange interactions are extracted from the temperature dependence of the susceptibility and amount to ∼ 200 K. The intertetramer coupling leads to the development of long-range antiferromagnetic order at T N = 8 K. An unusual temperature dependence of the effective g tensors is observed, accompanied with a rotation of macroscopic magnetic axes. We explain this unique observation as due to site-selective quantum correlations.
We observe the excitation of collective modes in the terahertz (THz) range driven by the recently discovered Néel spin-orbit torques (NSOTs) in the metallic antiferromagnet Mn_{2}Au. Temperature-dependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 to 450 K softens and loses intensity. A comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMR absorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by 3 orders of magnitude. Based on this and the agreement with our theory modeling, we infer that the driving mechanism for the observed mode is the current-induced NSOT. Here the electric field component of the THz pulse drives an ac current in the metal, which subsequently drives the AFMR. This electric manipulation of the Néel order parameter at high frequencies makes Mn_{2}Au a prime candidate for antiferromagnetic ultrafast memory applications.
We have studied the charge density wave ͑CDW͒ repolarization dynamics in blue bronze by applying square-wave voltages of different frequencies to the sample and measuring the changes in infrared transmittance, proportional to CDW strain. The frequency dependence of the electrotransmittance was fit to a modified harmonic oscillator response and the evolution of the parameters as functions of voltage, position, and temperature are discussed. Resonant frequencies decrease with distance from the current contacts, indicating that the resulting delays are intrinsic to the CDW with the strain effectively flowing from the contact. For a fixed position, the average relaxation time has a voltage dependence given by 0 ϳ V −p , with 1 Ͻ p Ͻ 2. The temperature dependence of the fitting parameters shows that the dynamics are governed by both the force on the CDW and the CDW current: for a given force and position, both the relaxation and delay times are inversely proportional to the CDW current as temperature is varied. The long relaxation and delay times ͑ϳ1 ms͒ suggest that the strain response involves the motion of macroscopic objects, presumably CDW phase dislocation lines.
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