Tricritical phenomenon and H − T phase diagram in a single crystal of the double-perovskite iridate La 2 ZnIrO 6

We report a detailed study of magnetic properties in double perovskite iridate ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal, which exhibits an antiferromagnetic (AFM) ground state. The field- and angle-dependent magnetizations $[M(H)$ and $M(\ensuremath{\varphi})]$ suggest strong magnetic anisotropy in this system. The magnetization of ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ is isotropic in the $ab$ plane, while it is much stronger than that along the $c$ axis. A field-induced magnetic transition from AFM to ferromagnetic (FM) state is found, which is of a first-order type. The critical behavior is investigated, where critical exponents $\ensuremath{\beta}=0.2317(1),\phantom{\rule{0.28em}{0ex}}\ensuremath{\gamma}=0.9783(2)$, and $\ensuremath{\delta}=5.0071(5)$ are obtained. The critical exponents belong to the universality class of the tricritical mean-field model, which indicates a field-induced tricritical phenomenon. Based on the scaling equations, we construct the $H\text{\ensuremath{-}}T$ phase diagram for ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal with $H//b$. A tricritical point is revealed at the intersection point between the AFM, FM, and paramagnetic phases (${T}_{tr}\ensuremath{\approx}8$ K; ${H}_{tr}\ensuremath{\approx}170$ Oe).