Magnetic and dielectric properties in the langasite-type compounds: A3BFe3D2O14 (A = Ba, Sr, Ca; B = Ta, Nb, Sb; D = Ge, Si)

The Fe-based langasites are the only reported compounds presenting a magnetic ordering in this rich family, besides being well known for piezoelectric properties and optical activity. The structural, magnetic, and dielectric properties of the Fe-langasite compounds, with various substitution of nonmagnetic cations, have been studied with x-ray and neutron-diffraction, magnetostatic measurements, Mossbauer spectroscopy, and dielectric measurements. The title compounds (trigonal space group P321) display a helical magnetic order with signatures of frustration below T-N approximate to 24-35 K, where an anomaly of the dielectric permittivity is observed. The influence of the cationic substitutions and the nature of the magnetoelectric coupling are hereafter addressed.