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The magnon propagation length (MPL) is one of the crucial factors to govern spin transport in a magnetic material. Here, we determine MPL ($\xi$) in compensated ferrimagnetic Gd3Fe5O12 (GdIG) thin films at room temperature by investigating longitudinal spin Seebeck effect (LSSE) in Gd3Ga5O12 (GGG)/GdIG($t$)/Pt (5 nm) heterostructures with different thicknesses ($t$) of the GdIG film. All films possess in-plane (IP) magnetic easy axis, and the compensation temperature shifts down to lower temperature with decreasing GdIG thickness. At room temperature, the LSSE signal is rather constant with thickness between $t = 221$ and 89 nm, but drops significantly below $t = 50$ nm. By fitting the thickness dependence of the LSSE voltage to a modified atomistic spin model considering the influence of saturation magnetization, we obtain $\xi $ = 45 nm ± 8 nm for GdIG thin films at room temperature. The MPL of GdIG is much shorter than that of Y3Fe5O12 films ($\xi $ ~90–140 nm), but higher than that of Fe3O4 films ($\xi $ ~20 nm). The obtained value of $\xi $ explains the drop in the LSSE voltage in GdIG films when the film thickness is reduced below 50 nm, knowledge of which is also essential to the design of spincaloritronic devices based on GdIG films. [ABSTRACT FROM AUTHOR]

The damping parameter ${\alpha }_{\mathrm{ FM}}$ in ferrimagnets defined according to the conventional practice for ferromagnets is known to be strongly temperature-dependent and diverge at the angular momentum compensation temperature, where the net angular momentum vanishes. However, recent theoretical and experimental developments on ferrimagnetic metals suggest that the damping parameter can be defined in such a way, which we denote by ${\alpha }_{\mathrm{ FiM}}$ , that it is free of the diverging anomaly at the angular momentum compensation point and is little dependent on temperature. To further understand the temperature dependence of the damping parameter in ferrimagnets, we analyze several datasets from literature for a ferrimagnetic insulator, gadolinium iron garnet, by using the two different definitions of the damping parameter. Using two methods to estimate the individual sublattice magnetizations, which yield results consistent with each other, we find that in all the used datasets, the damping parameter ${\alpha }_{\mathrm{ FiM}}$ does not increase at the angular compensation temperature and shows no anomaly, whereas the conventionally defined ${\alpha }_{\mathrm{ FM}}$ is strongly dependent on the temperature. [ABSTRACT FROM AUTHOR]

The electromagnetic (EM) properties of shielded gyromagnetic spheres are characterized with the aid of an electrodynamic model formulated for the transverse electric (TE) modes of an isotropic sphere, in a similar way as dielectric resonators are commonly analyzed. Broadband characteristics of geometric and energy filling factors are presented. A new measure of the magnetic loss tangent is introduced which is positive despite the intrinsic permeability of the gyromagnetic medium being negative, where existing definitions yield a non-physical negative value. The sample size dependence of those quantities is also assessed. The conclusions from the analysis are applied to investigate and de-embed ferromagnetic linewidth errors which can occur in broadband measurements of magnetic garnet spheres. Magnetic anisotropy fields and the gyromagnetic $g$ -factor are also estimated from the measurement data. Experiments were performed in a two-port subwavelength cavity, covering a frequency range of up to 28 GHz. Additionally, two-port rectangular resonant cavity linewidth measurements at a few modes have been conducted. Good agreement between the two methods is found if the systematic error is accounted for. [ABSTRACT FROM AUTHOR]

We report a study on the interfacial antiferromagnetic coupling between ferrimagnetic TbIG/YIG thin films. TbIG/YIG bilayers are grown on YAG (110) substrates. The crystal structure and magnetic properties of the films are characterized. The temperature and directional dependences of the antiferromagnetic coupling effect are observed at low temperatures. This work enriches the magnetic research of ferrimagnetic oxide films with complex structures, providing new ideas for the design of antiferromagnetically coupled spintronics devices. [ABSTRACT FROM AUTHOR]

Direct epitaxial integration of magnetic layers with wide bandgap nitride semiconductors will enable spin-controlled transport and photonic phenomena, seeding ideas for functional spintronic devices. Using plasma-assisted molecular beam epitaxy (MBE) in a previously unexplored window, significantly improved ferrimagnetic Mn4N layers are successfully grown on GaN with ~1 nm surface roughness. Distinct from earlier reports, the Mn4N layers grown on GaN are found to be [001] oriented with 12-fold in-plane symmetry in the diffraction pattern. This unique epitaxial registry originates from three equivalent rotational domains. The ferrimagnetic magnetotransport properties of low growth temperature Mn4N layers on GaN are comparable to those reported on cubic substrates such as MgO. However, a sign-flip of the Hall resistance is discovered for Mn4N layers grown above 300 °C. [ABSTRACT FROM AUTHOR]

An advanced digital feedback algorithm providing defined waveform shapes of magnetic flux density (as well as induced voltage) is demonstrated. The algorithm is based on the iterative process predicting the exciting field waveform to be used in order to achieve the desired waveform of the voltage induced in the secondary winding along with the use of advanced hardware configuration utilizing appropriate exciting power amplifier (AMP) acting as a voltage-to-current converter. An approach based on the inverse function computation [inverse function digital feedback (IFDF)] applied to the response of the sample under test (SUT) to the initial exciting field waveform was used to estimate the exciting field that should be applied to magnetize the sample. SUT is usually made of ferromagnetic/ferrimagnetic material, thus constituting basically a nonlinear hysteretic system. Due to the nonlinearity and hysteresis, the iterations have to be repeated more times until the differences between actual and ideal waveforms fit into the required limits based on the chosen criteria, such as form factor (FF), total harmonic distortion (THD), and sample Pearson’s correlation coefficient (rxy). The effectiveness of the algorithm is subjected to testing on various magnetic materials in a wide range of frequencies and amplitudes of the exciting field/flux density in order to judge its robustness and stability as well as the number of iterations steps (or time) needed to obtain the satisfactory waveform shape. [ABSTRACT FROM AUTHOR]

Compared with ferromagnetic counterparts, antiferromagnetic materials are considered as the future of spintronic applications since these materials are robust against the magnetic perturbation, produce no stray field, and display ultrafast dynamics. There are (at least) two sets of magnetic moments in antiferromagnets (AFMs) (with magnetization of the same magnitude but antiparallel directions) and ferrimagnets (with the magnetization of the different magnitude). The coupled dynamics of the bipartite collinear AFMs is modeled by a coupled system of Landau–Lifshitz–Gilbert equations with additional terms originated from the interlattice exchange, which leads to femtosecond magnetization dynamics in AFMs. In this article, we develop three Gauss–Seidel projection methods for micromagnetics simulation in AFMs and ferrimagnets. They are first-order accurate in time and second-order accurate in space, and only solve linear systems of equations with constant coefficients at each step. Femtosecond dynamics, Néel wall structure, and phase transition in the presence of an external magnetic field for AFMs are provided with the femtosecond stepsize. [ABSTRACT FROM AUTHOR]

We studied the phase stability of Ce-substituted magnetoplumbite-type Sr ferrite under various oxygen pressures. We have successfully obtained Ce-substituted samples as revealed from X-ray diffraction and wavelength dispersion X-ray analyses. The solubility limit of Ce in Sr1-xCexFe12O19 was estimated to be $x = 0.24$ at ambient pressure, which is reduced to 0.05–0.10 under higher oxygen pressures. The variation of the $c$ -axis against $x$ and the reduction of the solubility by increasing oxygen pressure suggests that the valence of Ce is not 4+ but 3+. The solubility limit of Ce is dominated not only by the ionic radius but also by the valence instability of Ce. [ABSTRACT FROM AUTHOR]

We investigate some critical phenomena of a Ising ferrimagnetic system on a square lattice with spins $Q=\pm 7/2, \pm 5/2, \pm 3/2$ , and ±1/2 in a $B$ sublattice and spins $S=\pm 5/2, \pm 3/2$ , and ±1/2 in a $A$ sublattice in presence of an $h'$ external magnetic field, such that $Q$ and $S$ are the nearest-neighbors ferrimagnetically coupled. Using Monte Carlo simulations, we calculate the finite-temperature phase diagrams of magnetization, specific heat, and magnetic susceptibility of the model. The system is defined by a Hamiltonian $(\mathcal {H})$ that contains ferromagnetic next-nearest-neighbors interactions between $S$ spins ($J'_{2}$), as well as external magnetic field and anisotropy interactions at each point of lattice. For a defined range of parameters in $\mathcal {H}$ , the system exhibits discontinuities in their physical variables and spin compensation behaviors. In the planes $J'_{2}-k_{\mathrm{ B}}T'$ and $h'-k_{\mathrm{ B}}T'$ , we analyze the relationship between the critical, compensation, and discontinuous phase transition temperatures with the external magnetic field and the next-nearest-neighbors interaction between $S$ spins. We found that the existence of discontinuous phase transition depends on the strengths of $h'$ and $J'_{2}$. [ABSTRACT FROM AUTHOR]

The Monte Carlo simulation has been used to investigate the magnetic properties of a mixed spin-1 (sublattice A) and spin-1/2 (sublattice B), where each sublattice has a rectangular structure and the whole lattice system forms a 2-D centered rectangular lattice. Five possible interactions are considered. Namely, two S–S interactions and two $\sigma $ – $\sigma $ interactions depend on crystal direction, and an antiferromagnetic interaction between the two sublattices is taken. Our results show that the critical temperature increases with increasing the variation of any exchange interactions. The existence of the compensation temperature depends on the balance between the S–S interactions along and $\sigma $ – $\sigma $ interactions along [01] directions. [ABSTRACT FROM AUTHOR]

Gold (50 nm)/bismuth ferrite (BFO) (100 nm) metal-semiconductor Schottky junction is fabricated using pulsed laser deposition (PLD) method on a Si substrate. BFO (BiFeO3) target for PLD deposition was made using BFO nanoparticles synthesized through sol-gel method. The forward- and reverse-bias current-voltage (I-V) characteristics of Au/BFO junction exhibit rectifier characteristics. The threshold voltage (Vγ) is 0.3 V which is in agreement with that of a conventional Schottky diode. I-V measurements were done with and without dc magnetic fields (H) to show the tuning of threshold voltage and forward-bias diode current. I-V characteristic shows distinct hysteresis behavior indicating hysteretic switching. Further, the fabricated diode was used as a half-wave rectifier. It has been demonstrated that the Au/BFO Schottky diode is a better high-frequency signal processing diode in comparison to a normal p-n junction silicon diode. Output waveforms were taken over a range of frequencies for both Au/BFO and Si diodes. An Si diode cannot rectify above 10 kHz, whereas Au/BFO junction diode can rectify even up to 1-MHz frequency. At high-frequency, Au/BFO diode exhibits “capacitor filtering effect,” resulting in higher dc voltages. [ABSTRACT FROM AUTHOR]

All-optical switching (AOS) is an emerging recording technology by using femtosecond laser to manipulate the ultrafast magnetization reversal for future super high density magnetic storage. TbCo films possess a ferrimagnetic structure and large perpendicular anisotropy and, thus, become a potential material for AOS. In this paper, we simulate the ultrafast magnetization reversal domain of Co-sublattice in TbCo films under 100 fs pulse laser with a general theoretical framework, and our simulation results show that TbCo films irradiated with a higher power fluence laser have a larger reversal domain of Co-sublattice due to the higher peak temperature and the further critical isotherm of electrons. Moreover, high Co content can help Co-sublattice form a large reversal domain, but is unable to obtain the highly uniform reversal domain perhaps attributed to the insufficient anti-ferromagnetic interaction between Tb atoms and Co atoms. [ABSTRACT FROM AUTHOR]

Microwave properties of a novel and functional composite inorganic materials based on barium hexaferrite (BaFe12O19) were measured and simulated. Three different inks with flake and sphere shape particles were developed and printed on the top of meander-shaped microwave inductor on alumina substrate. Several types of meandered inductors with a different number of turns were investigated for the verification of obtained results. The results show relative permeability values of 1.3, 2.2, and 1.5 for composite layers printed from the inks with flake shape at 41.5 wt.%, flake shape plus dodecyl benzene sulphonic acid (DBsa) at 44.4 wt.%, and sphere-like shape at 55.6 wt.% of BaFe12O19, respectively, at 3 GHz. Corresponding magnetic loss tangents were 0.015, 0.04, and 0.02. This novel inductor composite material can be applied for mobile telecommunication operations at 0.5 to 3 GHz frequency range. [ABSTRACT FROM AUTHOR]

A method that allows the determination of magnetic permeability in magnetic bodies, as well as the ferromagnetic resonance (FMR) linewidth, by measuring only the quality factor and the resonant frequency of the perturbed microwave cavity at FMR is presented. The method is based on a set of equations derived for various types of magnetic media, including ferrites, single crystals, and polycrystalline materials. The evaluation of resonators containing magnetic medium is considered, and a detailed description of the spectrometer and the experimental procedure are presented. Independently measured yttrium iron garnet samples were used to validate the method. [ABSTRACT FROM PUBLISHER]

Bulk CoCr2O4 undergoes a transition from paramagnetic to long-range ferrimagnetic phase at Tc (94 K) to a long-range and/or short-range spiral order at Ts ( \sim 24 K), and finally shows a lock-in-transition below 15 K. The spiral component induces an electric polarization and also a spontaneous magnetization for which it is said to be multiferroic. Reducing the size of a CoCr2O4 multiferroic material to \sim 50 nm by a coprecipitation method, we obtain a pure cubic phase with space group, Fd3m and lattice parameter (8.334 ± 0.003 °A). A rich sequence of magnetic transitions are examined by measuring temperature and field-dependent magnetization and diffused neutron scattering (DNS) using polarized neutron at different temperatures. While paramagnetic to ferrimagnetic transition is enhanced from 97 K in bulk to 99 K at 0.5 kOe field, followed by a decrease in lock-in-transition ( TL ) from 15 K in bulk to 8 K, spiral ordering temperature does not show a significant change. A strong disagreement between paramagnetic moment obtained from the fitting of \chi ^{-1}=({T}/{C})+({1}/{\chi o})-({b}/{T-\theta }) and ferrimagnetic moment obtained from the $M$ versus H$ loop taken at 2 K, nonsaturated magnetization at 50–100 kOe field, two order of magnitude higher coercivity ( H_{c} ), and splitting of ac susceptibly confirm the core–shell structure of the particles. Furthermore, a magnetic scattering analysis clearly shows that while the paramagnetic to ferrimagnetic transition is continuous, the spiral ordering is sharp, short range, and commensurate in contrast to incommensurate spiral order observed single crystal of CoCr2O4. [ABSTRACT FROM PUBLISHER]

The ferrimagnetic Mn2−xCoxSb ( $x$ = 0.15 and 0.20) alloys were prepared by arc-melting technique. The structure, magnetic, and magnetocaloric properties on these compounds were investigated. The tetragonal Cu2Sb-type structure ( $P$ 4/nmm space group) was confirmed by X-ray powder diffraction measurements at room temperature for these two alloys. The Co-introduction results in a first-order magnetic transition between the antiferromagnetic and the ferrimagnetic state. Adopting the standard and loop process method, respectively, the measurements of isothermal magnetization were performed and the magnetic entropy changes were evaluated for these alloys. [ABSTRACT FROM AUTHOR]

We investigated the anomalous Hall effect and longitudinal magnetoresistance in ferrimagnetic Co90Gd10 thin films with thicknesses from 5 to 35 nm and temperatures from 80 to 300 K. As the temperature increases from 80 to 300 K, the saturation magnetization of Co90Gd10 increases from 720 to 844 emu/cm3. However, the scaling law \sigma xy – \sigma xx^{n} with $n =2.3$ holds surprisingly well. Our results indicate that the scaling law usually reported in ferromagnetic materials remains valid for ferrimagnetic materials, which undoubtedly suggested the universality of the scaling law. [ABSTRACT FROM AUTHOR]

The equilibrium magnetic and structural reference states of Co- and Cr-doped Ni2Mn1.5In0.5 Heusler alloy are investigated by means of the first-principles method using a supercell approach. Three different ferrimagnetic and one ferromagnetic (FM) spin configurations, as well as two supercells with different distributions of excess Mn and In atoms, were considered. It is found that for supercell #1, the FM spin state in austenite is stable, where the martensite with different spin configurations is unstable, while in the case of supercell #2, a ferrimagnetic configuration for both austenite and martensite is favorable. The different trends for martensitic transformation were studied by $c/a$ calculations for the tetragonal and orthorombic distortions of supercells along the $z$ -axis and the $y$ -axis, showing martensitic variants for supercell #2 at a ratio $c/a > 1$ and $c/a < 1$ . [ABSTRACT FROM AUTHOR]

A spatially dispersive nonlinear transmission line (NLTL) using axially biased ferrite as the nonlinear medium has been developed. The NLTL is frequency tunable from 0.95 to 1.45 GHz with adjustment of the axial biasing field. A circuit model describing the dispersion of the line has been developed and compared with experimental measurements and time and frequency domain simulations. Instantaneous peak power levels exceeding 100 MW and average power levels of 10s of MW with durations from 4 to 17 ns have been observed. [ABSTRACT FROM PUBLISHER]

The aim of this paper is the analysis of the multipactor effect in a parallel-plate waveguide when a ferrite slab, transversally magnetized by a static magnetic field parallel to the waveguide walls, is present. Employing an in-house developed code, numerical simulations are performed to predict the multipactor radio frequency voltage threshold in such a ferrite-loaded waveguide. Variations of the ferrite magnetization field strength and the ferrite slab height are analyzed. Effective electron trajectories are also shown for a better understanding of the breakdown phenomenon, finding different multipactor regimes. [ABSTRACT FROM AUTHOR]

Cobalt ferrite (CoFe2{O_4}) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore, post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe2{O_4} nanoparticles with coercive magnetic flux density (Hc) in the range 5.5\–31.9~\kA/m and Ms in the range 47.9\–84.9~\A\cdot\m^2\Kg^-1. At a grain size of \sim 54 \pm 2~\nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in Hc. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe2{O_4} synthesis. The magnetic trends reported will aid in the optimization of functional CoFe2{O_4} nanoparticles. [ABSTRACT FROM PUBLISHER]

In this work, we report the synthesis, structure and magnetic properties of SrFe11T1O19 (T= \Ga,\Cr,\In,\Al) hexaferrite powders obtained by Pechini method. For all the samples, formation of the M-type structure was verified, together with a significant grain size coarsening, from 100 to 3000 nm. The magnetic properties include remarkable coercivity values of up to 590 kA/m, together with Curie temperatures within the range 652 K to 730 K across the compositional series. The coercivity variation was explained in terms of the evolution from single-domain magnetic particles to multidomain particles as a consequence of the significant grain growth. [ABSTRACT FROM PUBLISHER]

We have performed a combined study of magnetization hysteresis loops and time dependence of the magnetization in a broad temperature range for the ferrimagnetic \La2{\Ni}({\Ni}1/3{\Sb}2/3){\O}6 double perovskite. This material has a ferrimagnetic order transition at \sim100 K and at lower temperatures (\sim20 K) shows the signature of a frustrated state due to the presence of two competing magnetic exchange interactions. The temperature dependence of the coercive field shows an important upturn below the point where the frustrated state sets in. The use of hysteresis data, magnetization versus applied magnetic field, together with the magnetization versus time data provides a unique opportunity to distinguish between different scenarios for the low temperature regime. From our analysis, a strong domain wall pinning results in the best scenario for the low temperature regime. For temperatures larger than 20 K, the adequate scenario seems to correspond to a weak domain wall pinning. [ABSTRACT FROM PUBLISHER]

High-purity Tb3Fe5O12 samples were prepared by the solid-state reaction method at 1300–1390\,\,^\circ C and their magnetic and dielectric properties were studied. The results showed that although the magnetic properties did not change notably with the processing conditions used, the dielectric behaviors of the polycrystalline Tb3Fe5O12 were affected significantly. The increase of sintering temperature from 1300 to 1390\,\,^\circ C resulted in a dramatic increase in bulk density, dielectric constant and loss-peak frequency, but a decrease in the \alpha parameter of the Cole–Cole equation. The Fe^2+-Fe^3+ hopping process was proposed for the observed dielectric behaviors. The hopping activation energy, calculated by the Arrhenius plots, decreased from 0.438 to 0.289 eV as the sintering temperature increased from 1300 to 1390\,\,^\circ C . The Cole–Cole equation could be used to describe the relaxation behaviors of these samples and the calculated \alpha parameter decreased from 0.305 to 0.059. High sintering temperature had both the effects of improving crystallinity and enhancing the \ Fe^3+\rightarrow\ Fe^2+ reduction. The former lowered the hopping activation energy and narrowed the distribution of the relaxation time (as indicated by \alpha\rightarrow 0), while the later increased the dielectric constant and loss, as well as the DC conduction in the low frequency region. [ABSTRACT FROM AUTHOR]

Ultrafast demagnetization excited by laser pulses introduces the technological possibility for controlling the magnetic properties of materials on sub-picosecond regime. In this paper, the demagnetization dynamics of amorphous ferrimagnetic TbFeCo alloy is modeled by using the stochastic Landau-Lifshitz-Gilbert equation on an atomistic level. The transition metal (Fe, Co) and rare earth (Tb) atoms are constructed by two different sub-lattice systems. Laser-heating induced demagnetization processes are clearly demonstrated by a series of snapshots. Our simulations show that full demagnetization on the sub-picosecond time scale requires a temperature over the Curie point, and the demagnetization time increases with the Tb content. [ABSTRACT FROM AUTHOR]

Cavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing \mu-characteristics of ferrites when exposed to an external magnetic bias field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in W. R. Smythe “Reducing ferrite tuner power loss by bias field rotation,” IEEE Trans. Nucl. Sci., vol. 30, no. 4, pp. 273–275, 1983, but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1-directional magnetic bias. We have successfully tested this theory with a measurement set-up consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity Q and the possibility of fast tuning. In this paper, we describe the measurement set-up and present the tuning ranges that we attained by applying different bias schemes. [ABSTRACT FROM PUBLISHER]

Millimeter wave (MMW) absorption measurements have been conducted on commercial samples of large (micrometer-sized) and small (nanometer-sized) particles of BaFe12O19 and SrFe12O19 using a quasi-optical MMW spectrometer and a series of backwards wave oscillators encompassing the 30–120 GHz range. Effective anisotropy of the particles calculated from the resonant absorption frequency indicates lower overall anisotropy in the nano-particles. Due to their high magnetocrystalline anisotropy, both BaFe12O19 and SrFe12O19 are expected to have spin resonances in the 45–55 GHz range. Several of the sampled BaFe12O19 powders did not have MMW absorptions, so they were further investigated by DC magnetization and x-ray diffraction to assess magnetic behavior and structure. The samples with absent MMW absorption contained primarily iron oxides, suggesting that MMW absorption could be used for quality control in hexaferrite powder manufacture. [ABSTRACT FROM AUTHOR]

In particle accelerators, “field markers” provide a digital trigger when the magnetic field crosses a given threshold. In this paper, the metrological characterization of a magnetic field marker, based on a ferrimagnetic resonance transducer referencing the flux sensed by a coil, is reported. The experimental results of a validation test campaign at the European Organization for Nuclear Research (CERN) to test the marker in static as well as fast ramping fields (up to 2.5 T/s) are illustrated. The repeatability of \pm 4\ \muT attained in the range (60 to 100) mT is very promising to increase the performance of the Proton Synchrotron accelerator at CERN. [ABSTRACT FROM PUBLISHER]

Low temperature co-fired ceramic (LTCC) technology allows to create 3-D ceramic devices from tapes with different electrical and magnetic properties. Recently ferrimagnetic materials became available as LTCC tapes. To magnetically characterise the ferritic LTCC material we have realised ring samples using ESL 40012 LTCC-tapes. The ring core fabrication process and the sample preparation are described in detail. The quasi-static B(H) curve has been measured by inductive methods, and its dependence on temperature between room temperature and the Curie temperature is shown. [ABSTRACT FROM PUBLISHER]

We report a comparative study of magnetic and magnetoabsorption properties of bulk and nanoparticles of Ga2-xFe_xO3 (x\approx 1.25) compounds synthesized using sol-gel method. The average size of Ga2-xFe_xO3 nanoparticles is found to be 100 nm. We observe an enhancement in the ferrimagnetic transition temperature (TC=354\ K) of Ga2-xFe_xO3 nanoparticles compared to TC=298\ K of the bulk Ga2-xFe_xO3. The bulk and nanoparticles of Ga2-xFe_xO3 exhibit a large coercive field (HC) of HC= 0.95 and 0.8 T at T= 10 K, respectively and we observe that the HC decreases dramatically with increasing temperature. Magnetoabsorption was studied with a LC resonance technique and we found a close correlation between the shift in the resonance frequency due to applied magnetic field and the coercive field measured using dc magnetization measurements. We discuss the possible origins of the observed effects in both bulk and nanoparticles of Ga2-xFe_xO3 compounds. [ABSTRACT FROM AUTHOR]

In this paper, the influence of the layer thickness and the surface intralayer exchange coupling on the magnetic and thermodynamic properties of the mixed spin-2 and spin-5/2 ferrimagnetic systems are studied in detail by the Monte Carlo simulation. A number of interesting phenomena have been found. The results show that there exist the significant dependences of the compensation temperature, phase transition temperature, and the hysteresis loop of the system on both layer thickness and surface intralayer exchange coupling. [ABSTRACT FROM AUTHOR]

Distorted cubane [Mn^4+Mn3^{3+}{(\mu3-L^{2-})}3(\mu3-X^{-})(Z)^{3-}(dbm)3^{-}] (L=O; X=various; Z=(OAc)3; dbmH=dibenzoyl-methane) single-molecule magnets (SMMs) have been studied by first-principles calculations. Our earlier studies showed that the basic mechanism of antiferromagnetic Mn^4+-Mn^3+ coupling (JAB) is determined by the \pi type hybridization among the dz^{2} orbitals at the Mn^3+ sites and the t2g orbitals at the Mn^4+ site through the p orbitals at the \mu3-L^{2-} ions. This result allows us to predict that ferrimagnetic structure of Mn^4+Mn3^{3+} molecules will be the most stable with the Mn^4+-(\mu3-L^{2-})-Mn^{3+} angle \alpha\approx 90^\circ, while synthesized Mn^4+Mn3^{3+} molecules have \alpha\approx 95^\circ. One approach is suggested to design new Mn^4+Mn3^{3+} SMMs having a much more stable ferrimagnetic state. This approach is controlling the Mn^4+-(\mu3-L^{2-})-Mn^{3+} exchange pathways by rational variations in ligands to strengthen the hybridization between Mn ions. In this paper, by combining variations in the L and Z ligands, ten new high-spin [Mn^4+Mn3^{3+}{(\mu3-L^{2-})}3{(\mu3-F^{-})}3(Z)^3-(CH(CHO)2)3^{-}] (L=NCGeH5, NGeCH5, NGe2H5, NSiGeH5, or NGeSiH5; Z=(OAc)3 or MeC(CH2NCOMe)3) molecules have been designed. Our calculated results show that these ten modelling Mn4 molecules have \alpha\approx 90^\circ and JAB/kB in the range of (-231.6, -147.4) K, in which the molecule with [L,Z]=[NCGeH5,MeC{(CH2NCOMe)}3] has the highest JAB/kB of -231.6 K corresponding to \alpha=89.23^\circ. This value is over 3 times larger than that of synthesized Mn4 SMMs. Our calculated results demonstrate combining variations in the L and Z ligands as an effective way to tailor intramolecular exchange coupling of the Mn4 molecules. The results would give some hints for synthesizing new SMMs. [ABSTRACT FROM AUTHOR]

Ferrite nanoparticles are in the last years a matter of strong interest due to the fact that nanoscale materials possess size-dependent optical, electronic, magnetic, thermal, mechanical, and chemical properties that are comparable to or superior to those of bulk material counterparts, as well as its potential applications in sensors or microwave devices. Nickel ferrites, which are well-known technological materials in various electronic devices, were prepared in the form of nanoparticles by a modified sol-gel technique employing coconut oil, and then annealed at different temperatures in the 400° C-1200 ° C range. This route of preparation has been revealed to be one efficient and cheap technique to obain high-quality nickel ferrite nanosized powder. Sample particle sizes obtained with X-ray diffraction data and Scherrer's formula lie in 13-138 nm, with increased size with annealing temperature. Magnetic field-induced microwave absorption in nanoscale ferrites is a recent an active area of research, in order to characterize and explore potential novel applications. In the present work, microwave magnetoabsorption data of the annealed nickel ferrite nanoparticles are presented. These data have been obtained with a system developped in our laboratory, based on a network analyzer that operates in the frequency range 0-8.5 GHz. We can observe a resonance peak with applied fields of up to 400 mT. The results are interpreted on the basis of ferromagnetic resonance theory. [ABSTRACT FROM AUTHOR]

NiZn-ferrite materials are commonly used soft ferrites in all sorts of devices utilizing ferrimagnetic properties in a frequency range up to several tens of megahertz. Manufacturer data sheets of material properties usually contain values for the initial permeability for a given amplitude of the flux density for different frequencies, and some numbers for the loss factor. Strictly, these values are reasonable for steady-state processes with harmonic excitations only. Informations about the transient behavior of the material are contained in a single (dis)accommodation factor, if present at all. The phenomena of (dis)acconunodation or generally the change of the magnetic properties with time are explained by the magnetic aftereffect (MAE). We describe a measurement system to characterize the transient magnetic properties of ferrite rings, and present some results for a commercial ferrite torus. In contrast to measurement systems working with impedance analyzers (LCR-meter) or with resonant circuits, our system gives results with a much higher time resolution. The behavior of the material can be determined almost from the very first beginning of the excitation. [ABSTRACT FROM AUTHOR]

Birds, fish, sea turtles, and various other animals have been reported to sense the geomagnetic field and to use it for orientation, navigation, and homing. In recent years, exciting progress has been made towards elucidating the physical and structural basis of this remarkable phenomenon. This paper focuses on the two hypotheses that drive current research into magnetoreception. One proposal relies on the presence of molecules that undergo magnetically anisotropic chemical reactions due to transient formation of a radical pair. The proposed mechanism-essentially a chemical compass-is theoretically well-established and specifically designed behavioral experiments may indeed be interpreted that way, which has sparked a hunt for the molecules and structures in question. The ferrimagnetic transduction hypothesis, on the other hand, draws its plausibility from both theoretical considerations and the fact that magnetite has been detected in sensory neurons, with stable single-domain particles in fish and micrometer-scale clusters of superparamagnetic nanocrystals in birds. We discuss the limitations of our current knowledge and suggest future studies. [ABSTRACT FROM AUTHOR]

The effect of Al contents on the magnetic properties of Ba hexaferrite powders has been investigated in order to increase the coercivity. In this study, a self-propagating combustion method has been developed to form Ba hexaferrite nanopowders. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed that nanopowders with a size of 40-60 nm were successfully produced. With increasing Al contents, the coercivity of the nanopowders increased until the powders had a magnetoplumbite structure. We obtained a coercivity of 7559 Oe in BaFe10Al2O19 powders calcined at 850° for 1 h. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and power absorption properties of a series of magnetic nanoparticles (MNPs) of Fe3O4 with average sizes (d) ranging from 3 to 26 nm. Heating experiments as a function of particle size revealed a strong increase in the specific power absorption (SPA) values for particles with (d) = 25-30 nm. On the other side saturation magnetization Ms values of these MNPs remain essentially constant for particles with (d) above 10 nm, suggesting that the absorption mechanism is not determined by Ms. The largest SPA value obtained was 130 W/g, corresponding to a bimodal particle distribution with average size values of 17 and 26 nm. [ABSTRACT FROM AUTHOR]

We propose a method to determine the effective parameters for toroidal cores. We have found the method effective in generating the initial flux-magnetomotive-force curve, as well as minor and major flux-MMF loops for a wide range of commercial toroids, using three commercial power manganese-zinc (MnZn) ferrites. In the method, a material-dependent function is used to approximate the initial magnetization curve. Material-independent, geometry-dependent expressions are then derived for the effective parameters. We compare initial-magnetization-based Ie and Ae with those published by core producers. [ABSTRACT FROM AUTHOR]

Abstract-In this letter, we characterize the temperature dependence of the parameters of a frequency-dependent hysteresis model from room temperature to the Curie temperature, at different field amplitude and frequency. Empirical formulas based on power, rational, and gamma functions are suggested for the thermal variations to facilitate the use of the hysteresis model in computer- aided design. We demonstrate a parameter extraction procedure and provide experimental data for a commercial MnZn power ferrite magnetized up to 0.4 T, between 10 kHz and 1 MHz, and between 25 °C and 225 °C. [ABSTRACT FROM AUTHOR]

The high-temperature (T\geq 20\ K) magnetic properties of dysprosium iron garnet (DyIG) are theoretically presented in strong magnetic fields based on three-sublattice model. Under the consideration of the molecular fields among the different magnetic sublattices, our theory confirms that the magnetization in DyIG shows obvious isotropy with the increase of the temperatures. Also, at higher temperatures, the variations of the magnetization in DyIG with the magnetic fields (He) and the temperatures (T) are successfully fitted. Similar with the conclusion at low temperatures, it is also proved that the contribution of the magnetization of the rare-earth magnetic sublattice to the total magnetization in DyIG is greater than that of iron sublattices at higher temperatures. In addition, theoretical calculations reveal that the temperature and field dependence of the coefficients \alphai (i=a, c and d) associated with the molecular field parameters \lambda and magnetic susceptibility \chi, and at higher temperatures, it can be described as \alphai=P1+P2/He where P1 and P2 are the coefficients. [ABSTRACT FROM PUBLISHER]

We have investigated the thermal expansion of the ferrimagnet FeSe of the hexagonal system by synchrotron radiation powder X-ray diffraction from room temperature down to 90 K. The lattice constants show anisotropic change against temperature. Especially, the c-axis expands down to 170 K, exhibiting negative linear thermal expansion. Almost the same behavior is found in the temperature dependence of the magnetization. This implies that the anomalous change of the c-axis has a strong correlation with magnetism. Magnetic fields up to 0.4 T do not affect the lattice constants at room temperature. Electrical resistivity indicates metallic behavior, i.e., there is a finite density of the state at the Fermi energy, consisting of the Fe\ 3d and the Se\ 4p states. [ABSTRACT FROM AUTHOR]

Experimental studies on the complex susceptibility of soft magnetic composite materials (magnetostrictive Ni-Zn and Ni-Zn-Co spinels) in their region of ferrimagnetic resonance (FMR) show that the FMR is an increasing function of the applied pressure. It is shown that powders could advantageously replace their sintered materials counterpart to measure without any ambiguity the natural ferrimagnetic resonance (NFMR) frequencies of bulk materials. It is also shown that such soft ferrite composites can be realized in order to shift FMR to higher values, and to obtain low magnetic losses up to 900 MHz. High frequencies applications can be envisaged. [ABSTRACT FROM AUTHOR]

Nano-crystalline magnetite powder has been prepared successfully by self-propagating high-temperature synthesis (SHS) reaction using Fe, Fe2O3 and sodium perchlorate as starting materials. The synthesized powder has been subjected to intense milling using a planetary ball mill up to 10 h. The effects of Fe/Fe2O3 molar ratio as well as the milling time on the powder particle characteristics were investigated using XRD, SEM, TEM and VSM techniques. XRD results showed that the non-stoichiometric molar ratio (2.5 Fe+0.5 Fe2O3) is more favorable to synthesize magnetite phase. The phase composition was not affected significantly by milling process while both mean particle and crystallite size were decreased. Mean crystallite size of magnetite reduced from 90 to 40 nm after 10 h milling Saturation magnetization (Ms) increased from 47.6 in non-milled sample to 69.6 emu/g in milled sample for 10 h, while the coercivity (Hc) reduced from 365 to 120 Oe after milling. [ABSTRACT FROM AUTHOR]

Transmittance measurements on diluted barium ferrite materials in broadband millimeter-wave frequency range have been performed. The measurements have been done using free-space quasi-optical spectrometer in transverse magnetic field up to 7.5 kOe. A set of backward wave oscillators have been used as sources of high power coherent radiation tunable in 34–120 GHz frequency region. A magnetooptical approach has been employed for the separation of dielectric and magnetic effects in ferrites and simultaneous determination of complex dielectric permittivity and magnetic permeability of materials. It has been shown that a variation in the chemical composition of ferrites leads to a change in the magnetic properties and absorption of materials in the millimeter waves. [ABSTRACT FROM AUTHOR]

We report on the crystal structure and the magnetic properties of Mn5Sn3-xGax alloys with x = 0.1, 0.3, 0.5, 1.0, and 1.5, which were investigated by means of X-ray powder diffraction and magnetization measurements in fields up to 5 T in the temperature range 5 to 360 K. These alloys have in common that they exhibit a temperature-induced ferrimagnetic phase transition. The results indicate that all samples crystallize in the hexagonal Ni2 In-type structure with space group P63/mmc. The lattice parameters a and c of the Mn5Sn3-xGax decrease with increasing x, while the Curie temperature of these alloys increases with increasing x. All of the alloys exhibit a moderate magnetocaloric effect. Typical values are about 0.8 and 3 J/kgK at Tc = 282 K for x = 1.5 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively. [ABSTRACT FROM AUTHOR]

We present complex dielectric permittivity and magnetic permeability characteristics of strontium and nickel ferrite ceramics in Q-, V-, and W-band frequency range. The measurements have been done using broad-band quasi-optical millimeter wave spectrometer with backward-wave oscillator as a high power source of coherent radiation. Dielectric and magnetic parameters of the ferrite ceramic materials have been calculated by employing the best fit of the theoretical curves to the experimental transmittance spectra. [ABSTRACT FROM AUTHOR]

Reversal of synthetic antiferromagnetic and synthetic ferrimagnetic multilayer structures are studied theoretically in the precession-dominated regime. The role of key material and geometrical parameters for determining the switching characteristics and addressing regions are investigated. [ABSTRACT FROM AUTHOR]

Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be a triclinic superstructure of the NiAs structure while Fe/sub 7/Se/sub 8/ has a hexagonal structure. Changes of quadrupole shifts near 122 K for (Fe/sub 1-x/Ni/sub x/)/sub 7/Se/sub 8/ and 124 K for (Fe/sub 1-x/Co/sub x/)/sub 7/Se/sub 8/ indicate that the spin-rotation transition proceeds abruptly, in contrast to the gradual transition reported for Fe/sub 7/Se/sub 8/ with a triclinic superstructure. Isomer shifts indicate a ferrous character for the iron ions at all four sites. The Neel temperature is found to decrease with increasing nickel and cobalt concentration. [ABSTRACT FROM PUBLISHER]