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

Abstract

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 Ia3¯d 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 (α) and reduce the relaxation time in rare-earth doped YIG. α increased from 2.45 × 10−3 for un-doped YIG to 3.8 × 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.