  We report the discovery of linear magnetoelectric effect in the well-known
green phase compound, Sm2BaCuO5, which crystallizes in the centrosymmetric
orthorhombic (Pnma) structure. Magnetization and specific heat measurements
reveal the long-range antiferromagnetic ordering of Cu2+ and Sm3+-ions moments
at TN1 = 23 K and TN2 = 5 K, respectively. Applied magnetic field induces
dielectric anomaly at TN1 whose magnitude increases with field, which results
in significant (1.7%) magnetocapacitance effect. On the other hand, the
dielectric anomaly observed in zero-applied magnetic field at TN2 shows a small
(0.4%) magnetocapacitance effect. Interestingly, applied magnetic field induces
an electric polarization below TN1 and the polarization varies linearly up to
the maximum applied field of 9 T with the magnetoelectric coefficient {\alpha}
~ 4.4 ps/m, demonstrating high magnetoelectric coupling. Below TN2, the
electric polarization decreases from 35 to 29 {\mu}C/m2 at 2 K and 9 T due to
ordering of Sm-sublattice. The observed linear magnetoelectricity in Sm2BaCuO5
is explained using symmetry analysis.
