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At least 19 records

Structural elucidation, and morphological and magnetic behavior evaluations, of low-temperature sintered, Ce-doped, nanostructured garnet ferrites

Highlights: • Ce{sub x}Gd{sub 3.5-x}Fe{sub 4.5}O{sub 12} were synthesized via sol gel self-combustion route. • Crystallite size was found in the range of 20–38 nm. • Morphology of Ce-Gd doped and undoped garnets were observed systematically. • Switching field distribution was calculated for further applications of the nanoferrites. • These garnets also have potential applications in microwave high frequency devices. - Abstract: Low-temperature sintered Ce{sub x}Gd{sub 3.5-x}Fe{sub 4.5}O{sub 12} (x = 0.0, 0.4, 0.8, 1.2, 1.6, 2.0 and 2.4) garnet ferrites were synthesized via a sol-gel self-combustion route. Phase, structure, morphology and magnetic investigations were done using FTIR, XRD, FESEM, and VSM, respectively. Single-phase structures of all Ce{sup 3+} substituted nano-sized garnet ferrites were confirmed through XRD. The crystallite size was decreased with Ce{sup 3+}incorporation. Relevant structural parameters such as site radii, bond lengths, ionic radii, and shared edges were calculated using XRD. The vibrational spectroscopy stretching band studies were also done using FTIR. The grain size and morphology were also analyzed using FESEM. The magnetic remanance, saturation, and coercivity were found to increase systematically with an increase in Ce{sup 3+} concentration in these garnets. Switching field distribution curves were also plotted using the first derivative of the demagnetization data from MH loops. The better magnetic properties of these nanogarnets suggest their use for miniaturization of the devices in various applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magnetooptic Properties of Bismuth-Substituted Ferrite–Garnet Films in Strong Pulsed Magnetic Fields

Abstract—A technique of measuring the rotation of the light polarization plane in pulsed magnetic fields with strength up to 40 T with a sensitivity of 0.1° is proposed. The Faraday effect has been studied in films of diluted ferrites—garnets (Lu,Bi){sub 3}(Fe,Ga,Al){sub 5}O{sub 12} in the temperature range from room temperature to 78 K, including the vicinity of the magnetic moment compensation temperature. The transition to the noncollinear phase in the magnetic phase diagram is shown to occur at a magnetic field strength higher than 30 T at room temperature, and the threshold transition field tends to zero when approaching the magnetic moment compensation temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magnetic Phases and Inhomogeneous Micromagnetic Structures in a Ferrite Garnet Film with Orientation (210)

Possible magnetic states of a cubic ferromagnet with a uniaxial anisotropy induced along the [210] direction are theoretically investigated. It is demonstrated that the orientation phase diagram of a magnet is nontrivial and admits the existence of three types of magnetic phases that differ in transformational properties and the presence of quintuple points, isostructural phase transitions, etc. It is found that magnetic inhomogeneities, regardless of the values of parameters of the matter, have a common structure: they correspond to 180-degree domain boundaries with a noncircular trajectory of the magnetization vector. The features of homogeneous and inhomogeneous magnetic states, found in these materials, make it possible to explain the manifestation of a flexomagnetoelectric effect in them.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Dependence of the spin-wave resonance spectra in ferrite–garnet films on the microwave field frequency and damping parameter

The factors affecting the slope of the dispersion curve of the spin-wave resonance spectrum in multilayer films are determined. It is shown that an increase in the slope of the curve for the transverse orientation of the constant magnetic field relative to the film upon an increase in frequency is due to enhancement of dynamic as well as dissipative mechanisms of spin pinning. It is found that an increase in the damping parameter increases the degree of spin pinning in the case when the pinning layer is a reactive medium for spin oscillations and can decrease the degree of pinning when it is a dispersive medium. The conditions ensuring a higher degree of accuracy in determining the exchange interaction constant from the spin-wave resonance spectrum in multilayer films are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Determination of the concentration of conduction electrons in Y{sub 3}Fe{sub 5}O{sub 12} garnet crystals

Ferrites (garnets) are a model object of study and a promising material to be used in magneto-optical devices for data recording and processing and IR modulators. Due to the narrow ferromagnetic resonance line, optical transparency, and high elastic Q factor of ferrite single crystals, they are promising for solid-state microwave, optoelectronic, and computation devices. To ensure the optimal application of ferromagnetic materials, it is necessary to complete the following important task: develop a certification for samples with allowance for the degree of their imperfection caused by the deviation of crystals with garnet structure from stoichiometry, the competitive incorporation of process and dominant impurities, oxygen vacancies, etc.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Investigation of a stripline transmission line structure for gyromagnetic nonlinear transmission line high power microwave sources

A stripline gyromagnetic nonlinear transmission line (NLTL) was constructed out of yttrium iron garnet ferrite and tested at charge voltages of 35 kV–55 kV with bias fields ranging from 10 kA/m to 20 kA/m. Typically, high power gyromagnetic NLTLs are constructed in a coaxial geometry. While this approach has many advantages, including a uniform transverse electromagnetic (TEM) mode, simple interconnection between components, and the ability to use oil or pressurized gas as an insulator, the coaxial implementation suffers from complexity of construction, especially when using a solid insulator. By moving to a simpler transmission line geometry, NLTLs can be constructed more easily and arrayed on a single substrate. This work represents a first step in exploring the suitability of various transmission line structures, such as microstrips and coplanar waveguides. The resulting high power microwave (HPM) source operates in ultra high frequency (UHF) band with an average bandwidth of 40.1% and peak rf power from 2 MW to 12.7 MW.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

(Y{sub 1–x}Bi{sub x})3(Fe{sub 1–y}Ga{sub y}){sub 5}O{sub 12} Solid Solution Region in the Ieneke Diagram

Garnet ferrites with the overall composition (Y{sub 1–x}Bi{sub x})3(Fe{sub 1–y}Ga{sub y}){sub 5}O{sub 12} (0 ≤ х ≤1, 0 ≤ y ≤1) have been synthesized and characterized by X-ray diffraction. A relationship has been demonstrated between an increase in the concentration of Ga{sup 3+} cations and an increase in Bi{sub 2}O{sub 3} solubility in ss-Y{sub 3}(Fe,Ga){sub 5}O{sub 12}.

36 MATERIALS SCIENCE↗

A Method for Analyzing the Domain Structure in Magnetic Powder Microparticles

A method for analyzing the domain structure in magnetic powder microparticles based on the Mössbauer effect is proposed. This method has been experimentally verified for gadolinium ferrite-garnet (Gd{sub 3}Fe{sub 5}O{sub 12}) powder particles 40 ± 5 μm in diameter in the vicinity of the magnetic compensation point T{sub cm} = 286 K. It is shown that ferrite particles are single-domain near T{sub cm} and pass to the multidomain state while moving away from T{sub cm}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magnetic and Dielectric Properties of Y{sub 3−x}Sm{sub x}Fe{sub 5}O{sub 12} (x = 0.0 to 3.0)

Single-phase polycrystalline samples of Y{sub 3−x}Sm{sub x}Fe{sub 5}O{sub 12} (x = 0.0–3.0) were prepared by using a solid-state reaction method. The lattice constant is found to increase from 12.372 Å for x = 0.0 to 12.524 Å for x=3.0. The substitution of Sm{sup 3+} at Y{sup 3+} site is confirmed from the red shift of Raman F{sub 2g} mode. Magnetization loops measured at room temperature and the analysis of initial magnetization curves show that saturation magnetization value decreases with an increase in Sm concentration due to the possible antiferromagnetic interaction. On the other hand, temperature variation of magnetization plots shows that all the samples exhibit ferrimagnetic transition with transition temperature in the range of 550 K for x = 0.0 to 573 K for x=3.0. The dielectric constant increases upon Sm substitution, and the analysis of impedance and dielectric spectra shows the contribution of both grains and grain boundaries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

One-step synthesis of homogeneous BaFe{sub 12}O{sub 19}/Y{sub 3}Fe{sub 5}O{sub 12} composite powders

Highlights: • A simple one-step sol–gel method was used to synthesize composite magnets. • The composite powders show good homogeneity and exchange coupling. • The M{sub r}/M{sub s} value increases with the BaM concentration. - Abstract: BaFe{sub 12}O{sub 19}/Y{sub 3}Fe{sub 5}O{sub 12} (BaM/YIG) composite powders were synthesized via a simple one-step sol–gel method. The phase composition and morphology of the as-synthesized composite powders were characterized using an X-ray diffractometer and a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The magnetic properties of the composite powders were investigated by a vibrating sample magnetometer. Compared with the composite powders prepared by the conventional physical mixing method, the BaM/YIG composite powders show better homogeneity and exchange coupling.

36 MATERIALS SCIENCE↗

Tuning magnetotransport in PdPt/Y{sub 3}Fe{sub 5}O{sub 12}: Effects of magnetic proximity and spin-orbit coupling

We report that anisotropic magnetoresistance (AMR) and anomalous Hall conductivity (AHC) in the Pd{sub 1−x}Pt{sub x}/Y{sub 3}Fe{sub 5}O{sub 12} (YIG) bilayers could be tuned by varying the Pt concentration (x) and also temperature (T). In particular, the AHC at low T changes its sign when x increases from 0 to 1, agreeing with the negative and positive AHC predicted by our ab initio calculations for the magnetic proximity (MP)-induced ferromagnetic Pd and Pt, respectively. The AMR ratio is enhanced by ten times when x increases from 0 to 1. Furthermore, the AMR of PdPt/YIG bilayers shows similar T-dependence as the magnetic susceptibility of the corresponding bulk Pd/Pt, also indicating the MP effect as the origin of the AMR. The present work demonstrates that the alloying of Pt and Pd not only offers tunable spin-orbit coupling but also is useful to reveal the nature of the AMR and AHC in Pt/YIG bilayers, which are useful for spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Resonant isolator for maser amplifier

An isolator is described for use in a low noise maser amplifier, which provides low loss across a wide bandwidth and which can be constructed at moderate cost. The isolator includes a train of garnet or ferrite elements extending along the length of a microwave channel parallel to the slow wave structure, with the elements being of staggered height, so that the thin elements which are resonant to the microwaves are separated by much thicker elements. The thick garnet or ferrite elements reduce the magnetic flux passing through the thin elements to permit altering of the shape of the thin elements so as to facilitate their fabrication and to provide better isolation with reduced loss, by increasing the thickness of the thin elements and decreasing their length and width.

Clauss, R. C.↗

Metal thickness dependence on spin wave propagation in magnonic crystal using yttrium iron garnet

Magnonic crystals (MCs) are key components for spin wave manipulation. MCs realized with periodically metallized surfaces have an advantage in ease of the fabrication, but the effect of the metal thickness has not been studied well. In this work, the metal thickness dependence on the transmission spectra of localized mode spin waves was investigated. The metal thickness over half of the skin depth was necessary to prevent strong attenuation of spin waves.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Nonlinear multiferroic phase shifters for microwave frequencies

A nonlinear microwave phase shifter based on a planar multiferroic composite has been studied. The multiferroic structure is fabricated in the form of a bilayer consisting of yttrium iron garnet and barium strontium titanate. The principle of operation of the device is based on the linear and nonlinear control of the phase shift of the hybrid spin-electromagnetic waves propagating in the bilayer. The linear control is realized with magnetic and electric fields. The nonlinear control is provided by the input power of microwave signal. The device showed a nonlinear phase shift up to 250°, electric field induced phase shift up to 330°, and magnetic field induced phase shift of more than 180°.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Electrically Controlled Logical Switch Based on a Step Yttrium–Iron Garnet Waveguide and a Piezoelectric Actuator

We have demonstrated the possibility of functioning a device based on a spin-wave waveguide containing two channels with different ferrite film thicknesses as a logical switch. For switching states, we have used the dependence of interference type (constructive or destructive) at the output converter common for two channels on the waveguide strain under action of the electrically controlled actuator.

30 DIRECT ENERGY CONVERSION↗

Spin wave localization in one-dimensional magnonic microcavity comprising yttrium iron garnet

We demonstrate the localization of magnetostatic surface waves, i.e., spin waves, in a one-dimensional magnonic microcavity substantialized with periodical conductivity modulation. The narrow localized state is observed inside band gaps and is responsible for a sharp transmission peak. The experimental results strongly agree with the theoretical prediction made with the shape magnetic anisotropy of the propagating medium composed of yttrium iron garnet taken into account.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Bonding mechanism of a yttrium iron garnet film on Si without the use of an intermediate layer

Direct bonding of yttrium iron garnet (YIG) on silicon without the use of an intermediate bonding layer is demonstrated and characterized using scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy. During the bonding experiment, the garnet is reduced in the presence of oxide-free silicon. As a result, a 5 nm thick SiO{sub 2}/amorphous-YIG bilayer is formed and welds the garnet to silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magneto-optical imaging technique for hostile environments: The ghost imaging approach

In this paper, we develop an approach to magneto optical imaging (MOI), applying a ghost imaging (GI) protocol to perform Faraday microscopy. MOI is of the utmost importance for the investigation of magnetic properties of material samples, through Weiss domains shape, dimension and dynamics analysis. Nevertheless, in some extreme conditions such as cryogenic temperatures or high magnetic field applications, there exists a lack of domain images due to the difficulty in creating an efficient imaging system in such environments. Here, we present an innovative MOI technique that separates the imaging optical path from the one illuminating the object. The technique is based on thermal light GI and exploits correlations between light beams to retrieve the image of magnetic domains. As a proof of principle, the proposed technique is applied to the Faraday magneto-optical observation of the remanence domain structure of an yttrium iron garnet sample.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗