Magnetic and dielectric study of R0.5Sr0.5MnO3 (R=Gd, Tb and Dy)

Magnetic and dielectric properties of perovskite manganites R 0.5 Sr 0.5 MnO 3 ( R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T g ∼ 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R 3+ and Sr 3+ settled randomly at the same crystallographic site. Dielectric constants for each material were ∼1000–10,000 between ∼50 and ∼300 K and showed broad maximums above T g . Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R /Sr site. The tan δ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3 d electrons.