Singlet state formation and its impact on the magnetic structure in the tetramer system SeCuO3

Abstract

We present an experimental investigation of the magnetic structure in a tetramer system SeCuO3 using neutron diffraction and nuclear resonance techniques. We establish a non-collinear, commensurate antiferromagnetic ordering with a propagation vector k = (0, 0, 1). The order parameter follows a critical behavior near TN = 8 K, with a critical exponent β = 0.32 in agreement with a 3D universality class. Evidence is presented that a singlet state starts to form on tetramers at temperatures as high as 200 K, and its signature is preserved within the ordered state through a strong renormalization of the ordered magnetic moment on two non-equivalent copper sites, mCu1 ≈ 0.4 µB and mCu2 ≈ 0.7 µB at 1.5 K. S1 S2 S3 S4 J 11 J 12 J 12 Cu2 Cu1 FIG. 1. (Color online) A single Cu2 -Cu1 -Cu1 -Cu2 tetramer, with shaded CuO4 plaquettes. Below a schematic drawing of spins and exchange interactions between them (see Eq. 1).

Triplons, magnons, and spinons in a single quantum spin system:SeCuO3

“…We find that I c is of the same order as I p , making their ratio far greater than those found in multimagnon scattering studies [39,40]. The LSW prediction for this ratio can be deduced from the spin reduction (quantum fluctuation renormalization) measured [32] on the Cu 2 sublattice, and as Table II makes clear the data exclude any straightforward multimagnon origin. We comment that highly unconventional multimagnon processes, such as those involving very strong magnon-magnon interactions, are hard to rule out, but that there is little evidence for these (such as decay of our observed magnons) in SeCuO 3 .…”

“…From Fig. 1(a), J connects Cu 2 spins through the SeO 3 tetrahedra, a superexchange path not so far considered [31][32][33][34]. This coupled-chain character provides an immediate indication for the origin of the continuum scattering in Figs.…”

“…The two approaches indicate the range of possible renormalization effects due to quantum fluctuations, which is widest at intermediate energies (corresponding to the spinon continua). The extent of renormalization to LSW theory in SeCuO 3 can be gauged from the magnetic order on the Cu 2 sublattice, which despite its three-dimensional (3D) nature is μ 2 < 0.8μ B [32]. The interactions J γ 12 induce order on the Cu 1 sublattice, although μ 1 ≈ 0.35μ B is very weak even at the lowest temperatures, and hence a full description lies well beyond the LSW approximation.…”

“…The S = 1/2 quantum magnet SeCuO 3 [30] has a monoclinic unit cell with space group P2 1 /n and lattice parameters a = 7.71 Å, b = 8.24 Å, c = 8.50 Å, and β = 99.12 • . Two [31], although this scenario cannot explain the magnetic susceptibility below 90 K. Recent nuclear quadrupole resonance measurements confirmed the formation of singlet states at T 200 K [32], and together with nuclear magnetic resonance, electron spin resonance, and torque magnetometry experiments [33,34] were interpreted as reflecting two essentially decoupled subsystems, the strong, local Cu 1 dimers and weakly coupled Cu 2 spins hosting magnetic order below T N = 8 K.…”

Sensitivity Enhancement of NMR Spectroscopy Receiving Chain Used in Condensed Matter Physics

“…Our first measurement was on the 63 Cu signal in SeCuO 3 (two sets of measurements) [17], while the second one was the 133 Cs signal in Cs 2 Cu 2 SnF 12 (three sets of measurements) [18]. A full description of the measurement setup is available in Table 1, while the NMR properties of the measured nuclei are presented in Table 2.…”