Thermodynamics of the Kitaev honeycomb magnet $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Ru}{\mathrm{Cl}}_{3}$ is studied for different directions of in-plane magnetic field using measurements of the magnetic Gr\"uneisen parameter ${\mathrm{\ensuremath{\Gamma}}}_{B}$ and specific heat $C$. We identify two critical fields ${B}_{c}^{\mathrm{AF}1}$ and ${B}_{c}^{\mathrm{AF}2}$ corresponding, respectively, to a transition between two magnetically ordered states and the loss of magnetic order toward a quantum paramagnetic state. The ${B}_{c}^{\mathrm{AF}2}$ phase boundary reveals a narrow region of magnetic fields where inverse melting of the ordered phase may occur. No additional transitions are detected above ${B}_{c}^{\mathrm{AF}2}$ for any direction of the in-plane field, although a shoulder anomaly in ${\mathrm{\ensuremath{\Gamma}}}_{B}$ is observed systematically at $8--10\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ . Large field-induced entropy effects imply additional low-energy excitations at low fields and/or strongly field-dependent phonon entropies. Our results establish universal features of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Ru}{\mathrm{Cl}}_{3}$ in high magnetic fields and challenge the presence of a field-induced Kitaev spin liquid in this material.

Angle-dependent thermodynamics of α -Ru Cl 3

Spin-1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii-Moriya interaction via mean-field approximation

In this paper, we investigate the magnetic behavior of a single-walled hexagonal spin-1 Ising nanotube by using the effective field theory (EFT) with correlations and the differential operator technique (DOT). The system consists of six long legs distributed parallel to each other on a hexagonal basis. Within each chain, spin sites are regularly  positioned and magnetically coupled through a J// exchange interaction along the chains and J⊥ between adjacent chains. Key equations of magnetization, susceptibility and critical temperatures are established, numerically resolved and carefully analyzed for some selected exchange couplings and various applied magnetic fields. In addition to the phase diagram, interesting phenomena are  noted, particularly for opposite exchange interactions where magnetization plateaus and frustration are discovered.

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Magnetic properties of six-legged spin-1 nanotube in presence of a longitudinal applied field.

We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii–Moriya interaction ( D ) and a uniform longitudinal ( H ) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N =2 spin (EFT-2) we calculate the phase diagram in the H – D plane on a simple cubic lattice ( z =6). We analyzed the cases: anisotropic Heisenberg – case I: ( Δ = 1 ) , anisotropic Heisenberg – case II: ( Δ = 0.5 ) and anisotropic Heisenberg – case III: ( Δ = 0 ) , where only second order phase transitions are observed.

Anomaly in the phase diagram of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii-Moriya interaction: A low temperature analysis

We study the magnetic properties of the two-dimensional anisotropic antiferromagnetic spin-1/2 Heisenberg model with Dzyaloshinskii-Moriya interaction and in-plane frustration included. The method of spin Green functions within the framework of Tyablikov's random-phase-approximation decoupling scheme is used in order to derive expressions for the spin-wave spectrum, sublattice magnetization and transition temperature. Based on these expressions we perform a detailed analysis of the influence of varying values of model parameters on its magnetic properties. The model is also applied to the high-Tc superconducting parent compound La2Cuo4 and our results compared to available experimental data.

Effects of frustration and Dzyaloshinskii-Moriya interaction on the spin-1/2 anisotropic Heisenberg antiferromagnet with the application to La2CuO4

Critical and reentrant behavior of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii–Moriya interaction in a longitudinal magnetic field

Walter E.F. Parente

Papers

Spin-1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii-Moriya interaction via mean-field approximation

Critical and reentrant behavior of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii–Moriya interaction in a longitudinal magnetic field

Anomaly in the phase diagram of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii-Moriya interaction: A low temperature analysis