Competing magnetic interactions in a spin- 12 square lattice: Hidden order in Sr2VO4

Abstract

With decreasing temperature Sr2VO4 undergoes two structural phase transitions, tetragonalto-orthorhombic-to-tetragonal, without long-range magnetic order. Recent experiments suggest, that only at very low temperature Sr2VO4 might enter some, yet unknown, phase with long-range magnetic order, but without orthorhombic distortion. By combining relativistic density functional theory with an extended spin-1/2 compass-Heisenberg model we find an antiferromagnetic singlestripe ground state with highly competing exchange interactions, involving a non negligible interlayer coupling, which places the system at the crossover between between the XY and Heisenberg picture. Most strikingly, we find a strong two-site "spin-compass" exchange anisotropy which is relieved by the orthorhombic distortion induced by the spin stripe order. Based on these results we discuss the origin of the hidden order phase and the possible formation of a spin-liquid at low temperatures.The Heisenberg model on a square lattice is one of the most widely studied models in statistical physics. The applicability of this model in modern solid-state physics has become popular after the discovery of layered high-T c superconductors, since the parent magnetically ordered compounds are often considered as quasi two-dimensional (q2D) systems [1], and, more recently, for the interest in the interplay between magnetism and superconductivity in Fe-based superconductors [2]. In the 2D Heisenberg model the relative strength and competition of antiferromagnetic nearest and next nearest neighbor interactions (J 1 and J 2 ) provides useful insights on the stability of specific types of magnetic order: J 1 favors the Néel order (e.g., cuprates [3]), J 2 favors the stripe (ST) order (e.g. few types of vanadates [4][5][6][7]), whereas a spin-liquid state is expected to emerge near the classical phase-boundary between the Néel and the ST orderings [8][9][10]. The inclusion of additional interactions (J 3 , J 4 , . . . ) leads to more exotic states [11], for example the enigmatic nematic phases recently found in Fe-based superconductors which arises from the strong competition between the ST and Néel order [12][13][14][15].Tetragonal Sr 2 VO 4 , isostructural to the high-T c parent compound La 2 CuO 4 and similar to layered vanadate Li 2 VOSiO 4 [4], provides an opportunity to explore the role of the various types of magnetic interaction at play in a square lattice, owing to the presumably weak interplane interaction between spin-1/2 V 4+ (d 1 ) layers. The complicated structural, magnetic, and electronic transitions observed in Sr 2 VO 4 , in fact, suggests a competition and/or coexistence of different magnetic phases [16][17][18][19][20][21][22][23][24]. Upon cooling, the crystal structure evolves from tetragonal to an intermediate phase (at T c2 ∼ 140K), and again to a tetragonal phase (T c1 ∼ 100K) with a larger c/a ratio [16]. In the intermediate regime, an anomaly in the susceptibility is observed at T M ∼ 105K, which was initially thought to originate from magneti...

Hidden magnetic order in the triangular-lattice magnet Li2MnTeO6

“…An unusual hidden magnetic ordering occurs in an insulating oxide Sr 2 VO 4 at low temperature [15][16][17][18][19], for which several possible scenarios have been mentioned including an orbital ordering triggered by Jahn-Teller distortion [15], an unconventional magnetic octupolar ordering [20], and a Néel order with muted order parameter of 0.06 μ B (compared to 1 μ B in a classical spin-1/2 system) [16,19]. A direct confirmation of the LRO and inhomogeneous magnetic state was obtained by µSR studies [17], while recent theoretical calculations predict the single-stripe magnetic ordering [18].…”

Control of superexchange interactions with DC electric fields

“…Ref. [41]). Note that t 0 and t 1 can be arbitrary, though they should be perturbative, as long as we consider the ratios J A (E)/J A (0) and J F (E)/|J F (0)| within our scheme.…”

Spin–orbit coupling, orbitally entangled antiferromagnetic order, and collective spin–orbital excitations in Sr2VO4

“…The earliest band-structure calculations [12] indicated a magnetic instability that was confirmed by studies based on local density approximation (LDA + U) and HF approximation [13], and a ferromagnetic (FM) insulating ground state was found in both methods. On the other hand, a relativistic density-functional theory combined with an extended spin-1/2 Heisenberg model suggested the formation of spin liquid at low temperature [14]. Studies based on first-principle calculation combined with path-integral renormalization group, where SOC was not incorporated, have examined the stabilization of different types of spin orderings such as FM, double stripe, parquet, and have ruled these out in favor of an AFM ground state with orbital order [13,15].…”