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In this paper, we designed, fabricated, and characterized a novel band-pass filter using ferrite nanoparticles as the active element in microstrip geometry. Two 50-Ω Cu transmitting/receiving antennas (one side fed and the other side shorted) were fabricated by photolithography on top of a thick layer of ferrites (Fe3O4) nanoparticles. The filter is based on ferromagnetic resonance. It is very compact and has very wide frequency tunability. Linear dependence is obtained between the resonance frequency and the applied dc magnetic field. The bandwidth and Q-factor of the filter are observed to be almost constant over the field range studied. Theoretical calculations have been performed considering the ferrite nanoparticles as an effective medium with effective demagnetization. The frequency for different applied fields was calculated for different volume fractions, and it is shown theoretically that the control of band-pass frequency can also be achieved by varying the volume fraction of the nanoparticles in the effective medium. [ABSTRACT FROM AUTHOR]

The magnetic properties of arrays of one-dimensional nickel nano-wires with high aspect ratio have been studied by a Network Analyzer based ferromagnetic resonance (NA-FMR) technique using a flip-chip method in frequency domain. The frequency-field data [fr (H0)] is observed to be tunable up to 14-16 GHz with an applied field (H0) of 4 kOe. The fundamental magnetic parameters such as the spontaneous magnetization, gyromagnetic ratio (γ), and magnetic anisotropies of the nanowires were derived from ƒr (H0) data. The resonarne response of the Ni nanowire is explained theoretically by calculating the transmission parameter using a simple method; where the nanowire in the alumina matrix is represented by an effective medium. The power transmitted per unit area in the coplanar waveguide transmission line with the sample is calculated from the Poynting vector using the RF field components at all positions around the signal line in the waveguide. [ABSTRACT FROM AUTHOR]

The temperature dependence of the ferromagnetic-resonance field (Hres) and line width (ΔH) of epitaxial Fe thin films were studied. It is observed that Hres increases whereas ΔH decreases with the increase in temperature. The change in Hres is governed by the temperature dependence of the saturation magnetization and the magneto-crystalline anisotropy energy of the film. The present low-temperature investigations of Hres obeys the well-known T3/2 Bloch law. The resonance line width as a function of temperature shows a transition temperature (T1) separating two different regimes. This behavior may be associated with the temperature dependence of the anistropy. The Hres results are confirmed theoretically by simulating the power absorbed at ferromagnetic resonance by using the Landau-Lifsthiz-Gilbert equation. [ABSTRACT FROM AUTHOR]

The dynamic excitations in the nano-sized Permalloy arrays exhibit a strong resonance mode in ferromagnetic resonance experiments (conventional as well as network analyzer based) for the magnetic field applied in the plane of the array and along the short axis and long axis of the arrays. In network-analyzer experiments, when the dc field was applied along the short axis of the arrays, the resonance frequency goes down with an increasing interstrip distance up to 1 μm and then saturates for higher values. This behavior clearly demonstrates the presence of dipolar interactions between the individual elements, resulting in the increased resonance frequency for the smaller spacing whereas when the field is applied along the long axis, the resonance frequencies go up with increasing interstrip distance. [ABSTRACT FROM AUTHOR]

We present results for tunable microwave band-stop and bandpass filters on a microstrip geometry. These structures, prepared by sputtering on GaAs substrates, are compatible in size and growth process with on-chip high-frequency electronics. For the notch filters, we observed power attenuation up to ∼100 dB/cm and an insertion loss on the order of ∼2-3 dB for both Permalloy- and Fe-based structures. The operational frequency ranges from 5 to 35 GHz for external fields below 5 kOe. We discuss methods to increase operational frequency and reduce device linewidth. Using these techniques we are able, for example, to obtain an operational frequency of 11 GHz at zero applied field and to narrow the device linewidth from 3 GHz to 330 MHz. The operational frequency, which can be obtained from the ferromagnetic resonance condition, is set by material properties such as saturation magnetization Ms, anisotropy fields, the gyromagnetic ratio, and the magnitude of an applied field H. Thus, by using different materials and external fields one can create devices which function over a wide range of frequencies. [ABSTRACT FROM AUTHOR]

We present here the application of an exchange spring multilayer system in an on-chip microwave device. The microwave devices were made in a coplanar geometry using a [SmCo/NiFe]10 sputtered multilayer structure as the active material. At low fields we find an up shift of the operational frequency by more than 15 GHz for the multilayer system compared to the NiFe alone. For higher fields (above 2 kOe) the increase in operational frequency is about 8-10 GHz. In contrast to previous results using an oriented SmCo film, we find in our polycrystalline film that there is not a large difference between frequencies measured with positive magnetic field compared to those measured with negative magnetic field. We studied multilayer systems with different thicknesses of NiFe. Magneto-optical Kerr effect measurements show a distinct uniaxial anisotropy for structures with 30-nm NiFe. Thinner NiFe films did not result in a clear anisotropy. Nonetheless, a substantial frequency shift was measured for all the samples. These measurements indicate that exchange coupled structures can substantially increase the frequency of signal processing devices. [ABSTRACT FROM AUTHOR]

Nonlinear effects in magnetic films are a subject of growing interest. The onset of parametric instability translates into practical power limits for microwave devices. Nearly all high-power studies were done in ferrites; recently, An et a!. investigated Permalloy. However, no work has been performed on planar devices or on iron films. Here, we investigate the transmission of cw microwaves in a 6-mm-long, 13-µm-wide and 200-nm-thick iron-based microstrip notch filter in the frequency domain. At a particular field, there are three regions in the transmission response. Up to a threshold power of Pcrit, the differential absorption of ferromagnetic resonance (FMR) is nearly constant as a function of input power. Above Pcrit, the sample absorption decreases significantly as the power is increased. In addition, we observe a subsidiary absorption (SA) peak at a frequency above that of the FMR. We observed butterfly-like curves (Pcrit versus applied static magnetic field H), similar to ferrites, for FMR as well as for the subsidiary absorption. We compare the strength of the critical rf field in Fe, YIG, and Permalloy. These numbers indicate that Fe in a microstrip geometry has a much higher power handling capability. Finally, our structures can also be used as a power limiter. The SA can be significantly increased at high powers, thus limiting the transmission in the frequency range where the SA occurs. The usual FMR peak can be used as a small-signal suppressor. [ABSTRACT FROM AUTHOR]

We study the focusing of bulk and surface spin waves in thin Yttrium iron garnet (YIG) films by solving the implicit dispersion relation obtained from the magnetostatic Maxwell equations. We then obtain constant frequency curves in k-space for the bulk and the surface modes. The focusing pattern is obtained from the slowness surface by finding the normal to the slowness surface and then evaluating the curvature at each point on the surface. It is found that the bulk modes are focused in four to eight distinct directions depending on the frequency and the applied magnetic field. The surface waves are not focused as strongly as the bulk waves. Furthermore, the focusing direction is tunable with the frequency and applied field. [ABSTRACT FROM AUTHOR]

We report a theoretical study of thermal hysteresis of thin Dy films. Large differences between the isofield magnetization curves during heating and cooling are found. The temperature width of the thermal hysteresis is tunable by the external field strength, ranging from 40 to 100 K, for external fields in the 50 Oe-1.5 kOe interval. [ABSTRACT FROM AUTHOR]

We theoretically study the relation between stripe domains at remanence and magnetic normal modes in a single crystal Co bar. We find different stripe patterns depending on field history and in each case the domain structure can be related to a soft mode that triggers a phase transition. The stripe domain structure when the external field is along the long axis of the bar is shown to be generated by a standing wave mode, which has the same spatial structure as the stripes. At all fields this mode has the lowest frequency of all the standing wave modes. This mode goes soft at a second-order phase transition where the stripe domains emerge. For other directions of the field, the symmetry of soft modes is found to be consistent with the change in symmetry of the ground state and that the phase transition can be first order. An analytical model relating phase transitions and soft mode behavior is also briefly discussed. [ABSTRACT FROM AUTHOR]

Recently, various groups have proposed competing relaxation mechanisms on the magnetization damping in thin magnetic films. We used the ferromagnetic resonance (FMR) technique to understand this behavior from FMR linewidths of sputtered thin Fe films sandwiched by normal metals (NM = Cu, Al, Ti, and Ta) of 30 Å on each side. We made samples of Fe(d)/GaAs(100), AI/Fe(d)/Al/GaAs(100), Cu/Fe(d)/Cu/GaAs(100), Ti/Fe(d)ITI/GaAs(100), and Ta/Fe(d)/Ta/GaAs(100), with d =20 to 300 Å. Δ H scales with d-2 in bare Fe/GaAs and AI/Fe(d)/Al series of samples following the well-known two-magnon mechanism. The sandwich Fe series with Cu, Ti, and Ta follow d-1 behavior attributed to recently proposed spin pumping process. After analyzing the data, we conclude Ti/Ta as good spin sink materials, with a mixing conductance twice/thrice larger than Cu. We termed Cu as poor spin sink material in the sandwich Fe structures. Our analysis shows that FMR linewidth data is a powerful tool to investigate interfacial transport properties of magnetic sandwich structures. [ABSTRACT FROM AUTHOR]

The magnetic/dielectric hybrid transmission line structures provide a new class of microwave/millimeter wave devices, useful for signal processing. Reduction of device dimensions in these magnetic monolithic microwave integrated circuits (M-MMICs) is important from the cost and reliability point of view. Here, we explore the transmission characteristics of Fe and Permalloy based microstrip filters with microstrips of different widths, lengths, and thicknesses. The gyromagnetic resonance occurs at microwave frequencies of up to 12 GHz for Fe and 5 GHz for Permalloy, even in the absence of any dc magnetic field. The resulting absorption yields the stop-band behavior of the device. Our microstrip geometry significantly boosts the operational frequency due to an induced shape-anisotropy. Different geometries induce different demagnetization factors and hence different resonance frequencies. We calculate the frequency-boosting characteristics of the devices due to induced shape-anisotropy and observed a good match to our measurements. [ABSTRACT FROM AUTHOR]