"5"7Fe-Kernresonanz zur Untersuchung von Verunreinigungen und Defekten in Yttriumeisengranat

Abstract

"5"7Fe-NMR is applied to study impurities and defects in yttrium iron garnet (Y_3Fe_5O_1_2), both in films grown by liquid phase epitaxy and in sintered polycrystalline samples. The NMR spectra and the nuclear relaxation have been investigated. Impurities can enter the garnet structure from the basic oxides (Ca,Si), the flux (Pb) or the crucible (Pt). A cation defect in the garnet structure causes a characteristic satellite structure in the NMR spectrum besides the main line caused by the unpertubed iron nuclei. The satellite structure depends on the lattice site where the defect is located. The satellite intensity is proportional to the defect concentration. The assignment of a given satellite to a specific defect can be made within a series of samples where the defect concentration is changed. Threevalent impurity cations cause satellites with a linewidth equal to the corresponding main line, whereas charged impurities produce broader satellites. This shows a correlation of at least one other defect in the neighborhood of the charged one achieving a local charge compensation. One specific defect, the so called anti-site defect Y"3"+ on octahedral ironsites can be observed in all samples in the range from 0.1 to 1% of the total Y content. In epitaxial films, the number of anti-site defects grows with the lead content. The nuclear spin-lattice relaxation time T_1, at T = 4.2 K shows large differences for different samples. A short T_1 in the range of 10 ms, often connected withe the relation T_2 #approx# 2 T_1, is attributed to the existence of Fe"2"+. With the addition of divalent impurities the relaxation behavior changes resulting in T_1 >> T_2 with T_1 in the range of seconds, which can be explained by the suppression of Fe"2"+-formation by the incorporated impurities. The nuclear relaxation is correlated with the optical absorption at #lambda# = 1.3 #mu#m of the garnet films in the way that a short T_1 is associated with a high absorption also caused by Fe"2"+ and vice versa. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2947) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman