Optical absorption spectra of erbium iron garnet (ErIG)

Absorption spectra of the transition⁴ I _15/2→⁴ I _9/2 have been measured in erbium iron garnet (ErIG). From these spectra the exchange tensors for four Kramers dubletts can be obtained. A tentative analysis of these data in terms of a phenomenological exchange Hamiltonian will be presented.     

Changes in optical absorption in iron garnet films due to impurity incorporation

The incorporation of impurities in films of Bi-substituted iron garnets grown by liquid phase epitaxy has been studied by successively adding small amounts of SiO₂ and CaCO₃ to the melt before film growth. It is found that very small additions of CaCO₃ to the melt profoundly influences the optical absorption coefficient and the electrical properties. The impurity absorption ofn-type YIG doped with Si⁴⁺ and Pb²⁺ ions is investigated and its wavelength dependence compared to that ofp-type YIG. The optical transitions involved in the impurity absorption of iron garnets are discussed in terms of transition reaction, photon energy and dependence on the impurity concentration. Depending on the photon energy, one or several transitions may give rise to impurity absorption.     

Calculated K x-ray absorption spectrum of calcium

The K X-ray absorption spectrum of calcium has been calculated using the results of a self-consistent energy band calculation by the augmented plane wave method. The computed spectrum is in good agreement with experiment.     

Spectral dependence of photoinduced optical absorption in doped yttrium iron garnet single crystals

The photoinduced optical absorption α of doped yttrium iron garnets (YIG) is investigated. It is found that the optical absorption α at a wavelength of 1.1 μm depends on the wavelength of irradiating light in the range 0.6–1.9 μm. It is demonstrated that, in the Y₃Fe₅O₁₂ crystal with an acceptor Ba impurity, the photoinduced increase in α is due to the formation of Fe⁴⁺ ions in octahedral sites. The charge transfer occurs through photoexcitation of the ⁶ A _1g (⁶ S) → ⁴ T _1g (⁴ G) and ⁶ A _1g (⁶ S) → ⁴ T _2g (⁴ G) transitions of octahedral Fe³⁺ ions. In the crystal with a donor Si impurity, the increase in α is caused by the formation of Fe²⁺ ions upon photoionization of silicon. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 7, 2001, pp. 1233–1235. Original Russian Text Copyright ? 2001 by Doroshenko, Nadezhdin.     

Optical absorption spectrum and crystal field of erbium aluminum garnet (ErAlG)

The optical absorption spectrum of Erbium Aluminum Garnet (ErAlG) has been measured between 12000 cm^?1 and 26000 cm^?1. The crystal field splitting of the terms⁴I_15/2,⁴I_9/2,⁴F_9/2,⁴S_3/2,²H_11/2,⁴F_7/2,⁴F_5/2,⁴F_3/2,²H_9/2 and⁴G_11/2 was determined from the spectra and has been analysed in terms of the usual parametrization scheme. Nine crystal field parametersA _l ^m 〈r ^l〉≡B _l ^m which are necessary to describe the crystal field with the symmetryD ₂ at the site of the rare earth ion, were fitted to the experimental data. The values are (in cm^?1):B ₂ ⁰=+160B ₄ ⁰=?160B ₆ ⁰=+30B ₆ ⁶=+80B ₂ ²=?100B ₄ ²=+140B ₂ ⁶=?40B ₄ ⁴=?1800B ₆ ⁴=?700 This result is compared with those obtained from similar analysis of other garnets.     

Spin reorientation in erbium iron garnet

⁵⁷Fe Mössbauer measurements in the temperature range from 1.5 to 297 K on erbium iron garnet confirm the occurence of a spin reorientation from the [ 100 ] to the [ 111 ] direction. They show that the reorientation takes place gradually between 74 and 95 K. The values and the signs of the quadrupole coupling constants at the octahedral and tetrahedral sites are determined.     

Magnetic anisotropy of europium in iron garnet

Magnetization measurements have been made of single crystals of europium iron garnet (EuIG), Ga-doped EuIG and Al-doped EuIG. Cubic anisotropy constants K₁ and K₂ have been evaluated from the magnetization curves. Temperature dependence and concentration dependence of the anisotropy are compared with the theory by Foglio and van Vleck.     

Crystal field effects in terbium iron garnet

The infra-red absorption spectrum of terbium iron garnet, (TbIG), has been recorded at liquid helium temperature. The energy level scheme was reduced and simulated within the frame of crystal field (cf) theory. The cf parameters of TbIG are not significantly different from those of terbium aluminum garnet, (TbAlG).     

Spin reorientation in silicon-substituted yttrium iron garnet

Mössbauer spectroscopy of a silicon substituted YIG containing 0.3 Si⁴⁺ per formula unit has shown that a spin reorientation, from [111] to [100], occurs between 265 and 80 K. The transitions occur by way of the magnetic space groups $\text{R}\text{3}\text{c}\text{′ →}\text{F}\text{2′}\text{d}\text{′}\text{→}\text{I}\text{4}{}_1\text{ac}\text{′}\text{d}\text{′}$. The broad spin reorientation is mainly a consequence of the persistence of a nonuniform distribution of Fe²⁺ ions over the octahedral sites.     

DCEMS of neon implantation in yttrium iron garnet

⁵⁷Fe-enriched, epitaxial Y₃Fe₅O₁₂ films have been implanted with 50 keV and 100 keV neon ions with a dose of 4·10¹⁴Ne⁺/cm². Depth-selective conversion electron Mössbauer spectroscopy has been performed at 300 K and 40 K. The results show that the 50 keV-implanted sample can be interpreted as an amorphous layer on top of an almost unperturbed YIG layer. In the 100 keV-implanted film a buried amorphous layer is observed.     

Magnetic properties on holmium iron garnet in high magnetic field. Optical absorption spectra in the infra-red region

On single crystals of holmium iron garnet (HoIG), magnetic properties have been studied in magnetic field up to 150kOe applied parallel to the main crystallographic directions in the 4.2–300K temperature range. Above 130 K, the magnetization is isotropic and linear magnetic field dependent as previously found in polycrystals and predicted by Néel's ferrimagnetic theory. Nevertheless the paramagnetic Curie temperature is much higher than the polycrystal value. Below 130K, due to the onset of the umbrella structure, the ferrite magnetization presents a non linear field variation with [111] as easy direction. The field evolutions of the anisotropy constants (K ₁ andK ₂) were calculated. Optical absorption measurements of both 5₈5I ₆ and 5I ₈5I ₇ transitions are reported and compared to the results of the literature in terms of inequivalent magnetic sites.     

Faraday rotation in single crystal erbium iron garnet

Measurements of the Faraday rotation of ErIG, Er₃Fe₅O₁₂, have been performed in the 4.2–300 K temperature range in magnetic field up to 20 kOe applied along the [111] direction and at 1.15 μm wavelength. The results are analysed under the assumption that the contribution of the Fe³⁺ ions to the total Faraday rotation is the same as that of YIG, Y₃Fe₅O₁₂. The temperature and field dependences of the contribution of the Er³⁺ ions are deduced. Both magnetic and electric dipole contributions of the Er³⁺ ions are calculated; the electric dipole coefficient C_e is found to present a linear temperature dependence between 30–300 K. The temperature dependence of the Faraday rotation susceptibility differs strongly from that of the magnetic susceptibility.     

The relaxation rate of europium in europium iron garnet

The relaxation rate of europium ions in europium iron garnet (EulG) was estimated by assuming that the crystal field is modulated by optical phonons. Mixing J = 2 states into the J = 0 and J = 1 states by the static rhombic fields breaks the “triangle selection rule” and makes possible this mechanism.It is concluded that the mechanism proposed here can be responsible of the order of magnitude of the line width in the ferrimagnetic resonance of EuIG, but to obtain the observed isotropy of the line width, it is necessary to make rather arbitrary assumptions concerning the dependence of phonon spectral density on frequency.     

Spin-lattice relaxation of Fe nuclei in yttrium iron garnet

Pulse measurements of T₁ for ⁵⁷Fe nuclei in very pure, single crystals of YIG are reported. The temperature was varied from 2° to 292°K, and the externally applied field ranged from 0 to 6000 Oe. The temperature variation of T₁ is quite strong, being three orders of magnitude in the range 2°–40°K. At constant temperature, T₁ changed approximately one order of magnitude between saturation field and 6000 Oe. The data are compared with the results of a calculation by Beeman and Pincus, in which a second-order Raman process and the three-magnon process are assumed to predominate below 50°K. Agreement is only qualitative, the experimental values of T₁ being larger than predicted. At 4.2°K in zero field, it is found that a polycrystalline sample containing particles of ≈ 5 × 10⁻⁴ cm dia. has a value of 1/T₁ which is some two orders of magnitude larger than for a macroscopic crystal. The presence of a relaxation mechanism associated with surface effects is suggested.     

Reversible-adsorption-induced variation of domain width in iron garnet films

It has been found using the Faraday-effect magneto-optic method that the width of magnetic domains of the labyrinth domain structure in bismuth-containing iron garnet films with perpendicular anisotropy changes considerably after the adsorption of methanol molecules. A maximum change in domain width of 50% has been observed in methanol saturated vapor. This effect is reversible. A decrease in domain width under adsorption has been attributed to a decrease in the effective constant of the perpendicular magnetic anisotropy of the film caused by the adsorption of methanol molecules.     

Low temperature magnetic structure of erbium iron garnet

The magnetic and crystallographic structure of erbium iron garnet {Er₃}[Fe₂](Fe₃)O₁₂ has been refined simultaneously from powder and single crystal neutron diffraction data. At 5 K the ferrimagnetic structure has a spin direction parallel to [100]. Magnetic moments of iron and erbium and canting angles for the erbium sublattices were derived in space groupI4₁/acd for 5 K<T<65 K. The magnetic moments of the two erbium sites are 6.9 _B and 4.3 _B at 5 K. An indication of further symmetry reduction of the magnetic structure from tetragonal to orthorhombic below 5 K is discussed.     

Nanocrystalline gadolinium iron garnet for circulator applications

Due to high resistivity and low microwave losses, gadolinium iron garnets (GdIG) are useful materials for non-reciprocal devices such as circulators or isolators. Keeping the miniaturization and cost reduction in mind, the trend is to modify the conventional methods of preparation of samples. In this connection we have synthesized nanocystalline GdIG by using the Microwave Hydrothermal method at 160 °C/45 min. As synthesized powders were characterized by using X-ray diffraction (XRD), transmission electron microscopy and Fourier Transform Infrared Spectroscopy. XRD patterns show the formation of a garnet phase with crystallite size varying between 19 nm and 40 nm. Differential Thermal Analysis studies were also carried out on the nanopowders. The powders were densified at a lower sintering temperature of 1100 °C/45 min using a microwave sintering method. The sintered samples were characterized by XRD and atomic force microscopy. The frequency dependence of complex permittivity and ferromagnetic resonance were measured in the K_a band frequency (27–40 GHz). Magnetic properties were also measured at room temperature.