Study of the magnetic disaccommodation in La doped YIG

Abstract

The relaxation of the initial magnetic permeability of La doped yttrium iron garnet (YIG) samples with nominal composition Y3-xLaxFe5O12 (0< x <0.6) is analysed in this work. The results show a very different behaviour depending on the sintering atmosphere used for the fabrication of the samples. Concretely, for the samples sintered in air, it just have been detected the usual relaxation peak found in YIG at 130 K. However, a new relaxation peak appears around room temperature for the samples sintered in CO2 atmos- phere when the La content is at least of 0.3. These results have been interpreted in terms of the formation of a secondary perovskite phase when the La solubility limit is reached. It is well known that Yttrium Iron Garnet (YIG) is a key material for the development of microwave devices due to its electrical and magnetic properties and the possibility of introducing a wide range of dopants for tailoring its properties. It is very usual the substitution of iron by metallic cations in tetrahe- dral or octahedral sites of the lattice (1-3). However, the substitution of part of yttrium ions in dodecahe- dral sites with a rare earth element has been also studied so far (4, 5), showing that the total substitution of Y by lighter 4f rare earth elements La, Ce, Pr and Nd is not possible, and that, above the solubility limit, a secondary perovskite phase forms together with the magnetic garnet. In this sense, it is essential to determine the solubility limit of each extrinsic cation in order to assure that single YIG phase is ob- tained. Recently, our group has shown (6) that the magnetic disaccommodation technique is a powerful tool to analyse the garnet-perovskite transition in rare earth element doped YIG. This technique consists in the time variation of the mobility of domain walls after a magnetic shock, and is shown by a temporal evolution of the magnetic permeability after a demagnetization stage. This kind of phenomena, which is strongly temperature-dependent, is undesirable from the technical point of view, as it represents an im- portant source of magnetic losses in these materials, but it is very useful for basic research because such studies yield information about lattice symmetry and dynamics. Its origin has been attributed to either the rearrangement or the diffusion of anisotropic point defects, such as lattice vacancies and interstitials, within the Bloch walls. In this work we have studied the effect of La doping on the magnetic disaccom- modation of YIG samples fabricated under different sintering atmospheres.