Complex magnetic order in the decorated spin-chain system Rb2Mn3(MoO4)3(OH)2

Abstract

Macroscopic magnetic properties and microscopic magnetic structure of Rb2Mn3(MoO4)3(OH)2 (space group P nma) are investigated by magnetization, heat capacity and single-crystal neutron diffraction measurements. The compound's crystal structure contains bond-alternating [Mn3O11] ∞ chains along the b-axis, formed by isosceles triangles of Mn ions occupying two crystallographically nonequivalent sites (Mn1 site on the base and Mn2 site on the vertex). These chains are only weakly linked to each other by nonmagnetic oxyanions. Both SQUID magnetometry and neutron diffraction experiments show two successive magnetic transitions as a function of temperature. On cooling, it transitions from a paramagnetic phase into an incommensurate phase below 4.5 K with a magnetic wavevector near k1 = (0, 0.46, 0). An additional commensurate antiferromagnetically ordered component arises with k2 = (0, 0, 0), forming a complex magnetic structure below 3.5 K with two different propagation vectors of different stars. On further cooling, the incommensurate wavevector undergoes a lock-in transition below 2.3 K. The experimental results suggest that the magnetic superspace group is P nma.1 (0b0)s0ss for the single-k incommensurate phase and is P n ma(0b0)00s for the 2-k magnetic phase. We propose a simplified magnetic structure model taking into account the major ordered contributions, where the commensurate k2 defines the ordering of the c-axis component of Mn1 magnetic moment, while the incommensurate k1 describes the ordering of the ab-plane components of both Mn1 and Mn2 moments into elliptical cycloids.

NaCo2(SeO3)2(OH): competing magnetic ground states of a new sawtooth structure with 3d7 Co2+ ions

“…This frustration index is very small compared to our previously reported sawtooth chain systems, Rb 2 Fe 2 O(AsO 4 ) 2 ( f = ∼20) 32 and Rb 2 Mn 3 (MoO 4 ) 3 (OH) 2 ( f = ∼24). 12…”

“…This frustration index is very small compared to our previously reported sawtooth chain systems, Rb2Fe2O(AsO4)2 (f = ~20) 32 and Rb2Mn3(MoO4)3(OH)2 (f = ~24). 12 Figure 3b shows the temperature dependence of the magnetic susceptibility (χ = M/H) for T < 25 K collected under various magnetic fields (H = 100 Oe, 1 kOe, 10 kOe, 30 kOe and 50 kOe) for both ZFC and FC measurement protocols focusing on the low temperature region. For a 100 Oe applied magnetic field, the FC and ZFC curves bifurcate at 11 K (T1), each exhibiting a broad hump before starting to go down at 6 K. Below 6 K, the magnetic susceptibility continuously drops with lowering temperature and at 2 K it reaches very close to zero.…”

“…This frustration index is very small compared to our previously reported sawtooth chain systems, Rb 2 Fe 2 O(AsO 4 ) 2 ( f = ∼20) 32 and Rb 2 Mn 3 (MoO 4 ) 3 (OH) 2 ( f = ∼24). 12 Fig. 3b shows the temperature dependence of the magnetic susceptibility (χ M/H) for T < 25 K collected under various magnetic fields (H = 100 Oe, 1 kOe, 10 kOe, 30 kOe and 50 kOe) for both ZFC and FC measurement protocols focusing on the low temperature region.…”

“…For example, the triangular spin tube, sawtooth (Δ-chain) chain and half sawtooth chains are seminal models in the field of frustrated 1D quantum magnetic systems. [9][10][11][12] In the sawtooth chain magnetic lattice, the corner-sharing magnetic triangles connect in an up and down fashion along the chain. Within each triangle, two crystallographically independent sites produce two different exchange parameters between the base-base ( J bb ) and the base-vertex ( J bv ) pathways.…”

“…The lowest excitation in a sawtooth chain with periodic boundary conditions is given by a kink-antikink pair, which has a dispersionless gap ΔE = 0.234J where J is the coupling between pairs of spins. [9][10][11][12][13][14][15][16][17][18][19][20] Moreover, in the classical limit, some sawtooth model systems possess zero energy flat-band modes, remarkably similar to a Kagome antiferromagnet (sawtooth magnetic lattice is a partial structure of the Kagome lattice). Strongly correlated flat-band systems with localized magnon states in high magnetic fields are the subject of intensive studies, as flat-band modes offer promising possibilities for manipulating the propagation of waves of any origin.…”