Unconventional magnetic field response of the hyperhoneycomb Kitaev magnet β−Li2IrO3

Abstract

We present a unified description of the response of the hyperhoneycomb Kitaev magnet β-Li 2 IrO 3 to applied magnetic fields along the orthorhombic directions a, b and c. This description is based on the minimal nearest-neighbor J-K-Γ model and builds on the idea that the incommensurate counter-rotating order observed experimentally at zero field can be treated as a long-distance twisting of a nearby commensurate order with six spin sublattices. The results reveal that the behavior of the system for H a, H b and H c share a number of qualitative features, including: i) a strong intertwining of the modulated, counter-rotating order with a set of uniform orders; ii) the disappearance of the modulated order at a critical field H * , whose value is strongly anisotropic with H * b < H * c H * a ; iii) the presence of a robust zigzag phase above H * ; and iv) the fulfillment of the Bragg peak intensity sum rule. It is noteworthy that the disappearance of the modulated order for H c proceeds via a 'metamagnetic' first-order transition which does not restore all broken symmetries. This implies the existence of a second finite-T phase transition at higher magnetic fields. We also demonstrate that quantum fluctuations give rise to a significant reduction of the local moments for all directions of the field. The results for the total magnetization for H b are consistent with available data and confirm a previous assertion that the system is very close to the highly-frustrated K-Γ line in parameter space. Our predictions for the magnetic response for fields along a and c await experimental verification. arXiv:1910.13925v1 [cond-mat.str-el]

Reentrant incommensurate order and anomalous magnetic torque in the Kitaev magnet β−Li2IrO3

“…However, most of these materials exhibit complex long-range magnetic orders at sufficiently low temperatures, indicating that other subdominant interactions between magnetic moments are present and may also have nontrivial bond-dependent character. Both experiment [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] and theory [27][28][29][30][31][32][33] have shown that these orders are fragile and can be efficiently suppressed by external magnetic field. It was also found that the competition between the external field and anisotropic bond-dependent exchange interactions gives rise to highly anisotropic magnetization processes and a variety of complex orders at intermediate fields [27][28][29][30][31][32][33].…”

“…Therefore, the purpose of this paper is to understand the recent torque measurements in β-Li 2 IrO 3 [26] and γ -Li 2 IrO 3 [12,13]. These two materials appear to have closely related local energetics [35], and we will therefore focus entirely on the hyperhoneycomb β-Li 2 IrO 3 [23][24][25][26]36,37], whose microscopic minimal model, the nearest-neighbor (NN) J-Kmodel, has been better understood [30,31,[38][39][40].…”

“…To this end, we generalize the semianalytical framework developed previously in Refs. [30,31,40] to study the field-induced phase diagram for fields in the ab, bc, and ac crystallographic planes. This framework builds on the idea that the incommensurate (IC) counterrotating order observed experimentally at zero field can be treated as a long-distance twisting of a nearby commensurate order with six spin sublattices [40].…”

Quantum-classical crossover in the spin- 12 Heisenberg-Kitaev kagome magnet

“…as can be seen from Eq. (18). This is precisely the condition that minimizes the classical energy of the KHAF [40,75,76].…”

“…Unlike isotropic Heisenberg magnets, these materials break explicitly the SU(2) spin rotational invariance down to a discrete subgroup which is set by the interplay of spin-orbit coupling, crystal field effects and electronic correlations. The resulting anisotropic exchange gives rise to a new type of magnetic frustration, different from geometrical frustration [10,11], a wealth of unusual magnetic orders with strong sensitivity to external perturbations [6,8,[12][13][14][15][16][17][18][19][20], as well as gapped and gapless spin liquids with fractionalized excitations [21]. In addition to the extensively studied layered honeycomb materials α-RuCl 3 , Na 2 IrO 3 and α-Ir 2 IrO 3 , and their 3D analogues (β-γ )-Li 2 IrO 3 , other geometriesincluding triangular, kagome, pyrochlore, hyperkagome and fcc lattices-have attracted a lot of attention because they combine the frustration from the competing exchange couplings with the geometric frustration of the underlying lattices [22][23][24][25][26][27][28][29][30][31][32][33].…”