  An orthorhombic compound, NaMnSbO4, represents a square net of magnetic Mn2+
ions residing in vertex-shared oxygen octahedra. Its static and dynamic
magnetic properties were studied using magnetic susceptibility, specific heat,
magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR)
and density functional calculations. Thermodynamic data indicate an
establishment of the long-range magnetic order with TN about 44 K, which is
preceded by a short-range one at about 55 K. In addition, a non-trivial
wasp-waisted hysteresis loop of the magnetization was observed, indicating that
the ground state is most probably canted antiferromagnetic. Temperature
dependence of the magnetic susceptibility is described reasonably well in the
framework of 2D square lattice model with the main exchange parameter J = -5.3
K, which is in good agreement with density functional analysis, NMR and ESR
data.
