Magnetic Critical Behavior of a Quasi Two-Dimensional Antiferromagnet MnTiO₃

The magnetic neutron scattering from a single crystal of MnTiO₃. has been studied. The static magnetic susceptibility has shown two dimensional character above T_N. The sublattice magnetization, however, follows a power law with β=0.32±0.01 as in a three dimensional antiferromagnet. A quasi elastic neutron scattering has been observed in the vicinity of the Néel temperature with anisotropic three dinaensional correlations. When temperature increases, the scattering profile transforms gradually to a ridge-like form, indicating that the two dimensional correlations develope at about 16 K above T_N. The values of critical exponents in the three dimensional critical region coincide with the theoretical values of the three dimensional Ising system.