Magnetic and crystallographic properties of rare-earth substituted yttrium-iron garnet

Yttrium Iron Garnet (YIG) is a versatile material for microwave device applications since last five decades. The goal of this investigation is to synthesize rare-earth doped YIG to be applicable for broad-band microwave and logic devices. YIG with lanthanide substitution of x = 0.15 atoms per formula unit(Y3-xRxFe5O12) was synthesized using conventional solid-state method (R = La, Nd, Ce). X-ray diffraction pattern confirms the cubic Ia (3) over bard symmetry in all the doped samples with significant change in lattice parameters, bond angles and cell volume (Nd-YIG having the highest). Microstructural analysis using high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) captures the well-defined d-spacings and grain boundaries, respectively. Raman spectroscopy confirms the significant distortion in FeO4 tetrahedron. X-ray photoelectron spectroscopy (XPS) verified the effect of doping of lanthanides (Rare earth: La, Nd, Ce) ions as well as the occurrence of Fe2+ and Fe3+ ion concentrations to support the magnetization increase (highest for Nd-YIG). The exchange interaction between Fe2+ and Fe3+ ions increases with rare-earth doping. Hence, saturation magnetization increases from 24.42 emu/gm for YIG sample to 26.23 emu/gm for Nd doped YIG sample. Room temperature microwave characteristics of lanthanide ions (La, Nd, Ce) doped YIG have been investigated using field sweep ferromagnetic resonance (FMR) technique in a broad frequency range (4-20 GHz) using the fabricated microstrip transmission line device. From the measured FMR fields and linewidths data dynamic parameters were derived. It is observed that rare-earth ions enhance the Gilbert damping parameter (alpha) and reduce the relaxation time in rare-earth doped YIG. a increased from 2.45 x 10(-3) for un-doped YIG to 3.8 x 10(-3) for Nd doped YIG samples. From the observed results, it may be concluded that the lanthanide doped-YIG can be a good candidate for broad-band-width microwave filters for higher-band 5G technology. The relaxation time reduced from 38.45 ns for YIG to 22.3 ns for Nd doped YIG which can be useful for designing high speed memory devices. (C) 2018 Elsevier B.V. All rights reserved.