Field-driven successive phase transitions in the quasi-two-dimensional frustrated antiferromagnetBa2CoTeO6and highly degenerate classical ground states

Abstract

We report the results of magnetization and specific heat measurements of Ba2CoTeO6 composed of two subsystems A and B, which are magnetically described as an S = 1/2 triangular-lattice Heisenberg-like antiferromagnet and a J1 − J2 honeycomb-lattice Ising-like antiferromagnet, respectively. These two subsystems were found to be approximately decoupled. Ba2CoTeO6 undergoes magnetic phase transitions at TN1 = 12.0 K and TN2 = 3.0 K, which can be interpreted as the orderings of subsystems B and A, respectively. Subsystem A exhibits a magnetization plateau at one-third of the saturation magnetization for the magnetic field H perpendicular to the c axis owing to the quantum order-by-disorder, whereas for H c, subsystem B shows three-step metamagnetic transitions with magnetization plateaus at zero, one-third and one-half of the saturation magnetization. The analysis of the magnetization process for subsystem B shows that the classical ground states at these plateaus are infinitely degenerate within the Ising model.

Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba$$_{2}$$MnTeO$$_{6}$$

“…For example, Ba CoTeO is a unique case of B-site ordered double perovskite, where Co ( S = 1/2) ions form two (triangular and honeycomb) subsystems. The spins on the triangular lattice behave as Heisenberg spins, while the spins on the honeycomb lattice show Ising like antiferromagnetic interactions 32 , 33 . Electron-spin resonance (ESR) and magnetization measurements show that applied magnetic field perpendicular to the easy-axis induces magnetization plateaus for both sub-lattices due to strong quantum effects of S = 1/2 spins 32 – 34 .…”

“…The spins on the triangular lattice behave as Heisenberg spins, while the spins on the honeycomb lattice show Ising like antiferromagnetic interactions 32 , 33 . Electron-spin resonance (ESR) and magnetization measurements show that applied magnetic field perpendicular to the easy-axis induces magnetization plateaus for both sub-lattices due to strong quantum effects of S = 1/2 spins 32 – 34 . Another interesting example is Sr CuTeO , a quasi-two dimensional Heisenberg antiferromagnet, where Cu ( S = 1/2) ions form a planar square lattice and develop Néel order below 29 K 35 .…”

Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba2CoTeO6ceramics

“…15,23 More recently, an investigation using BCTO single-crystals revealed two successive AFM phase transitions, at 12.0 K and 3.0 K, arising from independent spin ordering of two decoupled subsystems associated with the two inequivalent Co 2+ ions. 24 Indeed, BCTO belongs to a hexagonal P3m1 space group, 15 where two inequivalent divalent Co ions form two sub-lattices, one composed of almost cubic Co(1)O 6 octahedra and another of noncentrosymmetric Co(2)O 6 octahedra. Because of such a difference, each subsystem orders at a different temperature, via a different and particular mechanism: subsystem A, formed by Co(1)O 6 ordering at 3.0 K, subsystem B, formed by Co(2)O 6 ordering at 12.0 K. 24 As a result, the magnetic susceptibility is anisotropic showing a strong dependence on the crystal direction along which the magnetic field is applied and presents a maximum at around 20 K, with an inflection point at 15.0 K and a bend anomaly at 3.0 K. This low temperature AFM transition was observed to shift to lower temperature when the field was applied parallel to the c-axis of the single-crystal.…”

“…24 Indeed, BCTO belongs to a hexagonal P3m1 space group, 15 where two inequivalent divalent Co ions form two sub-lattices, one composed of almost cubic Co(1)O 6 octahedra and another of noncentrosymmetric Co(2)O 6 octahedra. Because of such a difference, each subsystem orders at a different temperature, via a different and particular mechanism: subsystem A, formed by Co(1)O 6 ordering at 3.0 K, subsystem B, formed by Co(2)O 6 ordering at 12.0 K. 24 As a result, the magnetic susceptibility is anisotropic showing a strong dependence on the crystal direction along which the magnetic field is applied and presents a maximum at around 20 K, with an inflection point at 15.0 K and a bend anomaly at 3.0 K. This low temperature AFM transition was observed to shift to lower temperature when the field was applied parallel to the c-axis of the single-crystal. Recent work 25 conducted at Los Alamos National Laboratory involving magnetostriction experiments in pulsed magnetic fields up to 60 Tesla provided data to construct a H-T phase diagram for H parallel and perpendicular to the c-axis of BCTO crystals.…”

Spin dynamics in the stripe-ordered buckled honeycomb lattice antiferromagnet Ba2NiTeO6

“…We note that Ba 2 CoTeO 6 also includes buckled honeycomb layers, 16 and exhibited interesting magnetic phases particularly in the magnetic field. 17 The material is, however, composed of two subsystems; a buckled honeycomb lattice and a triangular lattice.…”