Bose-Einstein condensation of triplons close to the quantum critical point in the quasi-one-dimensional spin- 12 antiferromagnet NaVOPO4

Abstract

Structural and magnetic properties of a quasi-one-dimensional spin-1/2 compound NaVOPO4 are explored by x-ray diffraction, magnetic susceptibility, high-field magnetization, specific heat, electron spin resonance, and 31 P nuclear magnetic resonance measurements, as well as complementary ab initio calculations. Whereas magnetic susceptibility of NaVOPO4 may be compatible with the gapless uniform spin chain model, detailed examination of the crystal structure reveals a weak alternation of the exchange couplings with the alternation ratio α 0.98 and the ensuing zero-field spin gap ∆0/kB 2.4 K directly probed by field-dependent magnetization measurements. No longrange order is observed down to 50 mK in zero field. However, applied fields above the critical field Hc1 1.6 T give rise to a magnetic ordering transition with the phase boundary TN ∝ (H − Hc1)

Quantum magnetism of ferromagnetic spin dimers in $α$-KVOPO$_4$

“…] is calculated to be ∼ 3937 Oe/µ B which matches nicely with the A iso hf value (∼ 3909 Oe/µ B ) obtained directly from the K iso vs χ analysis. This value of A iso hf is comparable with the values reported for other transitionmetal phosphate compounds [14,47,48].…”

“…Inter-estingly, the magnetization curve is nearly linear. Its curvature is smaller than in the other low-dimensional V 4+ magnets [21,35], including the AVOXO 4 compounds with A = Li, Na, and Ag [12][13][14]. Along with the FM Curie-Weiss temperature, this reduced curvature of M (H) sets α-KVOPO 4 apart from other V 4+ materials with the similar composition.…”

“…Quantum fluctuations manifest themselves by the short-range order that appears below 5 K and precedes the long-range order formed at T N = 2.7 K. Below T N , the commensurate and collinear ground state features a strongly reduced ordered magnetic moment of 0.58 µ B at 1.5 K. The unusually strong FM coupling J 1 is caused by the effective orbital order on the two crystallographically nonequivalent vanadium sites. Overall, from the magnetism perspective α-KVOPO 4 is entirely different from its siblings, such as NaVOPO 4 with its field-induced quantum critical point [14] and AgVOAsO 4 with the double-dome regime of magnon BEC [12]. The remarkable structural diversity of the V 4+ phosphates with their different connectivities of the vanadium polyhedra [58] suggests that further unusual regimes of magnetic couplings may occur in this broad family of compounds.…”

“…From the magnetism perspective, the crucial feature of AVOXO 4 is that their structural chains are not the direction of predominant magnetic interactions, even though the intrachain V-V distances are much shorter than the interchain ones [11,12]. It has been shown that monoclinic NaVOXO 4 [13,14] and AgVOAsO 4 [11,15], as well as triclinic ε-LiVOPO 4 [16], all adopt an intriguing pattern of crossed bond-alternating spin chains, which are perpendicular to the structural chains. These compounds reveal a field-induced quantum phase transition and an unusual double-dome regime of Bose-Einstein condensation (BEC) of magnons in high magnetic fields [12].…”

Quasi-one-dimensional magnetism in the spin- 12 antiferromagnet BaNa2Cu(VO4)2Sebastian1, Somesh2, Nandi3 et al. 2021Phys. Rev. BSelf Cite21080View full textAdd to dashboardCite

“…Such displacements do not occur in BaNa 2 Cu(VO 4 ) 2 , but they may potentially appear in sister compounds, because even the substitution of Na + by Ag + causes significant structural changes, although the two ions are very similar in size. Alternatively, one may consider structure types with a weaker spatial separation between the crossed chains that, in turn, allows several nonequivalent interactions to form a frustrated topology even in the absence of lateral displacements [64][65][66].…”