Quasi-two-dimensional ferromagnetism in the triangular magnet EuAl 12 O 19

We report ferromagnetic ordering at ${T}_{\mathrm{C}}=1.3\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in the quasi-two-dimensional magnet ${\mathrm{EuAl}}₁₂{\mathrm{O}}₁₉$ with large spins $S=7/2$. This ferromagnetic state was characterized by magnetization and specific heat measurements and the experimental results were compared with classical Monte Carlo simulations. They reveal a strong single-ion anisotropy leading to a uniaxial spontaneous magnetization along the $c$ axis. Furthermore, the application of a magnetic field in the hard magnetization plane $ab$ reduces the Curie temperature down to $T=0.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ at ${\ensuremath{\mu}}₀H\ensuremath{\approx}0.4\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ while preserving the second-order nature of the ferromagnetic transition.