Neutron study of the magnetism in NiCl₂⋅4SC(NH₂)₂

Abstract

We study the strongly anisotropic quasi-one-dimensional S = 1 quantum magnet NiCl2·4SC(NH2)2 using elastic and inelastic neutron scattering. We demonstrate that a magnetic field splits the excited doublet state and drives the lower doublet state to zero energy at a critical field Hc1. For Hc1 < H < Hc2, where Hc2 indicates the transition to a fully magnetized state, three-dimensional magnetic order is established with the AF moment perpendicular to the magnetic field. We mapped the temperature/magnetic field phase diagram, and we find that the total ordered magnetic moment reaches m(tot) = 2.1 μB at the field μ(0)H = 6 T and is thus close to the saturation value of the fully ordered moment. We study the magnetic spin dynamics in the fully magnetized state for H > Hc2, and we demonstrate the presence of an AF interaction between Ni(2+) on the two interpenetrating sublattices. In the antiferromagnetically ordered phase, the spin-waves that develop from the lower-energy doublet are split into two modes. This is most likely the result of the presence of the AF interaction between the interpenetrating lattices.

Dynamics of a bond-disorderedS=1quantum magnet nearz=1criticality

“…Note that next-nearest-neighbor interactions along the c axis could not be detected in the high-field experiment of Ref. 31, as their scattering plane was orthogonal to c. Analyzing the measured dispersion in DTNX, we find J c2 to be ferromagnetic, and therefore nonfrustrating. Both J d and J c2 corrections are relatively small, and don't qualitatively affect the general picture for DTN.…”

“…Applying this correction to the parameters in Table I results in the values, summarized in Table II. The parameters of pure DTN, determined from the spin-wave dispersion in the fully polarized phase, 31 are also given for comparison.…”

Microwave dynamics of the stoichiometric and bond-disordered anisotropic S=1 chain antiferromagnet NiCl2−4SC(NH2Soldatov1, Смирнов2, Povarov3 et al. 2020Phys. Rev. B5190View full textAdd to dashboardCite

“…The lowtemperature quantum disordered state of DTN was found to be unstable in the magnetic field H c1 = 21 kOe directed parallel to the four-fold axis c. In this field a quantum phase transition into the antiferromagnetically ordered phase occurs [5]. At this transformation the spin gap of excitations at the Brillouin zone boundary is closing [6]. In the field range H c1 < H < H c2 DTN is an antiferromagnet with magnon excitations.…”

Nuclear Magnetic Resonance Reveals Disordered Level-Crossing Physics in the Bose-Glass Regime of the Br-Doped Ni(Cl1−xBrxOrlova1, Blinder2, Kermarrec3 et al. 2017Phys. Rev. Lett.152390View full textAdd to dashboardCite

“…Between the two critical magnetic fields H c1 and H c2 , it presents a magnetic-field-induced low-temperature (T ) 3D-ordered phase, described as a Bose-Einstein condensate (BEC) [2][3][4][5]. DTN is particularly convenient for studying this phase; for a magnetic field (H) applied along the chain c axis, its (body-centered) tetragonal symmetry [6] ensures the required axial symmetry of the spin Hamiltonian with respect to H. The values of its exchange couplings and [7,8] make the BEC phase easily accessible, with H c2 = 12.32 T [9-11] and the phase transition temperature T c below T cmax = 1.2 K. The system can be reasonably considered as quasi-one-dimensional (1D), with J a,b /J c = 0.08.Br-doped DTN, Ni(Cl 1−x Br x ) 2 -4SC(NH 2 ) 2 (DTNX), allows studying the effect of a bond disorder, which may lead to the appearance of a localized Bose-glass (BG) phases adjacent to the (now inhomogeneous) BEC phase [12], as suggested from the thermodynamic measurements [13]. The BG state, first discussed for quantum wires [14] and superfluid 4 He absorbed in porous media [15,16], remains elusive, with only a few experimental examples [17][18][19][20], particularly rare for condensed-matter systems in the thermodynamic limit [21], such as DTNX [13].…”