Bloch lines in domain walls of antiferromagnets

Approximants describing the substructure of 180° domain walls in antiferromagnets with a high uniaxial anisotropy are derived. The structure and spectrum of Bloch lines separating the parts of domain walls with oppositely directed antiferromagnetic vectors are determined.     

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.     

Growth and characterization of cerium-substituted yttrium iron garnet single crystals for magneto-optical applications

This paper is concerned with the preparation and characterization of cerium-substituted yttrium iron garnets, which are known to be oxides having a large Faraday rotation effect. Using the improved flux method we successfully grew bulk single crystals of iron garnet doped with Ce³⁺ ions with maximum substitutions up to 0.349. Here we investigate different solution compositions for maximum Ce³⁺ substitution. The Faraday rotation and optical absorption spectra were measured in the near infrared region for different Ce³⁺ ion substituted iron garnets. The specific Faraday rotation of Ce_0.349Eu_0.195Y_2.456Fe₅O₁₂ was found to be 1430 deg/cm at a wavelength of 780 nm and –1280 deg/cm at 1150 nm. The Ce substitution prominently enhances the Faraday rotation effect, and Yb³⁺ and Eu³⁺ ions substituted for Y³⁺ in the dodecahedral sites of YIG can increase the concentration of Ce³⁺ ions, depressing the formation of nonmagnetic Ce⁴⁺ ions by charge compensation. Received: 24 January 2001 / Accepted: 2 March 2001 / Published online: 27 June 2001     

Spectrum of flexural oscillations of a domain wall with drifting Bloch lines

It is observed that in single-crystalline yttrium iron garnet the amplitude of characteristic flexural oscillations of a 180° domain wall containing Bloch lines increases sharply when drift of the Bloch lines is excited. The resonance frequencies of these oscillations are virtually identical to those of flexural oscillations of a monopolar wall. It is shown experimentally that this phenomenon is most likely caused by a magnetic aftereffect. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 72–75 (10 January 1998)     

Dynamics of antiferromagnetic vortices in yttrium orthoferrite domain walls

The total velocity of solitary flexural waves nonlinearly increases with an increase in the velocity of domain walls and becomes saturated at a level of 20 km s^?1; the smaller the wave amplitude, the more rapidly saturation occurs. Counter collisions of solitary flexural waves lead to the formation of a single wave with a difference amplitude moving in the same direction as the wave with a larger amplitude. The experimental results confirm that solitary flexural waves accompany antiferromagnetic vortices at domain walls in yttrium orthoferrite.     

Rotational hysteresis loss and anisotropy in yttrium garnet ferrite single crystals

The rotational hysteresis loss in Y₃Fe₅O₁₂ single crystals is found to increase with the field up to 2.5–3 kOe at all temperatures between –183 and 250 ° C, this being followed by a fall, a further peak at 8–10 kOe, and a slow fall, with some residual effect even at 20 kOe. This loss is sensitive to heat treatment; annealing for 2 hr at 275 ° C greatly reduces the loss at –183 ° C and halves the main (second) peak at 20 ° C. These anomalies do not occur in ferrites with the spinel structure. The first anistropy constant is slightly reduced at all temperatures as a result of annealing.     

Growth of yttrium iron garnet single crystals in Na2O-B2O3 flux system in air

Detailed studies of growth of yttrium iron garnet (YIG) in the flux system Na₂O-B₂O₃ were made to delineate the phase stability regions of YIG and the neighbouring crystalline phases, and a tentative working diagram of Na₂O-B₂O₃-YIG in air was drawn from the results of small batch crystal growth runs and solubility studies. The occurrence of a rather narrow field of YIG crystallization in this system was explained on the basis of relative solubilities of different oxides constituting YIG. Several long-time growth runs with some typical compositions were carried out in this system to evaluate its suitability for bulk growth of YIG crystals. The system, although possessing some inherent advantages, was found to suffer from limitations because of which the maximum size of the self-nucleated crystals grown hardly exceeded 2.00 mm.     

Observation of Bloch lines in yttrium orthoferrite

Utilizing the dark field method, parts of different brightness within domain walls of yttrium orthoferrite have been observed. Dark segments between these parts and the dependence of their positions on an applied magnetic field indicate the presence of Bloch lines.     

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.     

Spectrum of flexural oscillations of a 180-degree domain wall in yttrium iron garnet

The long-wave asymptotic behavior of the spectrum of flexural oscillations of a monopolar domain wall in a cubic ferromagnet is found. The experimental results, numerical calculations, and theoretical results obtained for uniaxial ferromagnets are compared. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 797–802 (25 May 1996)     

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.     

Layered structure of epitaxial yttrium iron garnet films

The layered structure of yttrium iron garnet films, ranging in thickness from 0.7 to 4.1 μm, grown epitaxially on single-crystal gallium-gadolinium garnet substrates, was investigated by x-ray spectral microanalysis. The ferrite films were chemically etched layer by layer in a mixture of orthophosphoric and sulfuric acids at T=353–423 K. It was established that the chemical composition of the films varies over the thickness because of the nonuniform distribution of gadolinium, gallium, lead, and platinum ions; the film-substrate transitional layer and the surface layer of the film differ most greatly with respect to the composition and magnetic properties. It was shown that the thickness of the transitional layers and their negative effect on the magnetic characteristics of ferrite films decrease appreciably if at the time of immersion of the substrate and pulling of epitaxial structure out of the fluxed solution the substrate holder together with a special mixer rotate at a rate of 50 rpm and the pulling velocity is 20 cm/min. Zh. Tekh. Fiz. 69, 62–64 (December 1999)     

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.     

Mobility of domain walls in low-loss garnet films

The dependence of the domain wall mobility on the strength of a static magnetic field applied in the plane of the sample is investigated in single-crystal garnet films of the system YBiFeGa with perpendicular magnetic anisotropy and a narrow ferromagnetic resonance line. It is shown that, as in the case of YIG single crystals with cubic magnetic anisotropy, wall motion gives rise to an additional energy loss contribution far greater than the relativistic contribution also present in the case of homogeneous magnetization. It is established that a mechanism recently proposed in theory does not give a correct explanation for this additional contribution, because qualitative as well as quantitative discrepancies exist between the theoretical conclusions and measurement data. Fiz. Tverd. Tela (St. Petersburg) 39, 1253–1256 (July 1997)     

Laser performance of highly neodymium-doped yttrium aluminum garnet crystals

The laser performance of highly neodymium-doped yttrium aluminum garnet (YAG) crystals is reported. In cw laser-diode pumping, a slope efficiency of 54% was achieved for a 2-at. %-doped sample, which was comparable with the slope efficiency of 55% of YVO(4) . The crystal also exhibited a slope efficiency of 64% under pulsed Ti:sapphire pumping. Such a high efficiency suggests a total cavity loss of ~1% , which is as low as that of commercially available 1-at. % YAG crystal. The excellent performance of the neodymium-doped YAG crystals indicates their high optical quality.     

Exchange coupling in ultrathin epitaxial yttrium iron garnet films

Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y₃Fe₅O₁₂ or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y₃Al₅O₁₂ or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied from 180 ? to 4600 ?. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis loops recorded for ultrathin YIG films have a “bee-waist” shape and show a coupling between two different magnetic phases. The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to be Y₃Fe_5-xAl_xO₁₂ due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures. This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling, the maximal interaction energy is estimated to be about 0.17 erg/cm² at 5 K for (111) oriented sample. Received 3 June 2002 / Received in final form 7 October 2002 Published online 27 January 2003 RID="a" ID="a"Presently at LPM, Université H. Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy e-mail: popova@lpm.u-nancy.fr     

Magnetic triangular bubble lattices in bismuth-doped yttrium iron garnet

Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet(Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete cir...