Multiferroicity Of Rare-earth Iron Garnet Ceramics

Rare earth iron garnet (RIG), a ferrimagnetic material known as microwave ferrite, has been widely applied in passive microwave devices and magneto-optical devices. Its magetic and magneto-optical properties have been widely investigated. Recently, the investigations of dielectric properties and magnetodielectric effects in RIG have been attracting much interest. In this work, structure, dielectric response, magnetic properties and magnetodielectric properties of rare earth iron garnet ceramics were investigated.In Y3Fe5.χAlχ-O12(x=0,0.5,1,2,3) ceramics, Rietveld refinement of XRD data suggests that Al3+substitutes for Fe3+at tetrahedral sites. All the samples show a giant dielectric response which originates from the charge carrier hopping between the Fe2+ and Fe3+. The activation energy of the hopping process increases with increasing Al substitution. The a-d super-exchange interaction becomes weak as the content of Al increases, which results in the decrease of saturation magnetizations and magnetic ordering temperatures.It was found that the dielectric constant and dielectric loss of Y3.rBiχFe5O12(χ=0, 0.5,1) ceramics decrease with increasing Bi amount. The saturation magnetization decreases and the magnetic ordering temperature increases as the amount of Bi increases. The contribution of the intrinsic and extrinsic effects to magnetodielectric effects decreases with increase of Bi, which results in the decrease of magnetodielectric coefficient of Y3-χBiχFe5O12ceramics.Ti substitution induces a low temperature dielectric relaxation which comes from the charge carrier hopping between Ti3+and Ti4+for Y3Fe5-χTiχO12+χ/2(χ=0,0.1,0.2) ceramics. The Maxwell-Wagner effect related dielectric relaxation becomes weak as the content of Ti increases. The contribution of the extrinsic effects to MD effect decreases and the contribution of the intrinsic effects to MD effect increases with increasing Ti amount, so the magnetodielectric coefficient first decreases and then increases.The coupling becomes weak with ionic radius decreases for Ln3Fe5Oi2(Ln=Sm, Y. Yb) ceramics, which enhances the response when magnetic field is applied. As a result, the magnetodielectric effect increases.