Investigation of structural, magnetic and dielectric properties of Al-doped samarium iron garnet

Polycrystalline Sm${}_3$(Fe${}_{1-x}$Al${}_x$)${}_5$O${}_{12}$ (x =0, 0.1, 0.2, 0.3, 0.4) samples were prepared in single phase form. Rietveld analysis of X-ray diffraction patterns shows that samples crystallize in cubic structure (space group: Ia$\overline{3}$d) with a systematic decrease in lattice constant with Al doping. Magnetization measurements show that all these samples exhibit ferrimagnetic transition whose transition temperature (T${}_c$) decreases from 562 K for x =0 to 350 K for x =0.4 due to the dilution of Fe${}^{3+}$-O–Fe${}^{3+}$ networks. In addition to that they undergo spin reorientation transition at T${}_{SR}$~ 70 K with considerable magnetic irreversibility below T${}_{SR}$. Interestingly the x =0.4 sample undergoes magnetic compensation at 26 K. Improvement of frequency response of dielectric constant (ε′) and loss tangent (tan δ) is observed upon Al doping in a wide frequency range of 10${}^2$-10${}^9$ Hz.