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The magnetic structures of the intrinsic magnetic topological insulator family MnBi2Te4(Bi2Te3)n (n = 0, 1, 2) adopt A-type antiferromagnetic (AFM) configurations with ferromagnetic (FM) MnBi2Te4 layers stacking through van der Waals interactions. While the interlayer coupling could be effectively tunned by the number of Bi2Te3 spacer layers n, the intralayer FM exchange coupling is considered too robust to control. Here, by applying hydrostatic pressure up to 3.5 GPa as an external knob, we discover the opposite responses of magnetic properties for MnBi2Te4(Bi2Te3)n with n = 1 and 2. In MnBi4Te7, the Né el temperature decreases with an increasing saturation field as pressure increases, indicating an enhanced interlayer AFM coupling. In sharp contrast, both the magnetic susceptibility and magneto-tranport measurements show that MnBi6Te10 experiences a phase transition from A-type AFM to quasi two-dimensional FM state with a suppressed saturation field under pressure. First-principles calculations reveal the essential role of the intralayer exchange coupling, which contains the competition between the AFM-preferred direct exchange and FM-preferred superexchange coupling, in determining these magnetic properties. Such a magnetic phase transition is also observed in Sb-doped MnBi6Te10 due to similar mechanism, where the in-plane lattice constant is effectively reduced.

One of the most important issues in modern condensed matter physics is the realization of fractionalized excitations, such as the Majorana excitations in the Kitaev quantum spin liquid. The 3d-based Kitaev candidate Na2Co2TeO6 is promising to realize such kind of spin liquid phase under external magnetic fields. Here, we first established a complete phase diagram comprising an intermediate magnetically disordered phase sandwiched by the zigzag ordered phase and the polarized trivial phase by the in-plane magnetic torque measurements. Then, the observations, including the restoration of the crystalline point group symmetry in the angle-dependent torque data and the coexisting spinons and magnons from the inelastic neutron scattering data, provide strong evidence that this disordered phase is a field induced quantum spin liquid with partially polarized spins. Our variational Monte Carlo simulation with the effective K-J1-Γ-Γ′-J3 model agrees well with the experimental data and further supports this conclusion.

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Cooperative Jahn−Teller (JT) distortion accompanied by electromagnetic lattice coupling plays a crucial role in numerous important phenomena in materials science. The JT distortion occurring in high-spin 3d 4 and 3d 9 configurations in octahedral complexes is common, but similarly, large distortion due to lifting the degeneracy of t 2g orbitals has so far seldomly been observed. Here, we report the discovery of the pressure-induced cooperative JT effect coupled with a large volume collapse of ∼12.8% and a magnetic moment collapse from S = 5/2 to S = 1/2 at ∼20.9 GPa in MnTe. The first-principles calculation indicates that weakened p−d hybridization and enhanced d state localization result in lifting t 2g orbital degeneracy in Mn 2+ (d 5 ), which induced a cooperative JT effect-triggered electromagnetic lattice coupling. These findings suggest a new mechanism for the cooperative JT distortion via pressure-induced ligand distortion in antiferromagnetic materials.