Y. V. Khivintsev

Iron-based microstrip band-stop filters at higher microwave frequency range: Design optimization using shape anisotropy

Microwave filters that use thin films of ferromagnetic metals are now being established as an option compared to YIG based filters due to their higher frequency response at very small magnetic fields. The aim of the present investigation is to significantly boost the operating frequency of notch filters in very low applied magnetic fields. To do this, we fabricated a series of notch filters with Fe films of different thicknesses and shapes. The stop-band response of each of these filters cover four waveguide bands (X, KU, K and Ka) ranging from 8to40GHz with an applied magnetic field up to 4.5kOe. The frequency characteristics of these filters at zero field can be significantly changed by changing the geometry of the magnetic element. For example, an Fe film which is 7.5μm wide, 100nm thick, and 3mm long has a stop band centered at 9.5GHz, but this is increased to 22GHz for an 800nm thick Fe film. For narrower signal lines (4.5μm wide), we observed further increases in the frequencies: 11GHz for a 100nm F...

Spin wave resonance excitation in ferromagnetic films using planar waveguide structures

We explore a new geometry allowing effective excitation of the lowest antisymmetric standing spin wave mode in ferromagnetic metallic films with symmetrical boundary conditions. The approach is based on the use of a coplanar waveguide with the ferromagnetic film, Permalloy (Py), playing the role of the signal line. In addition, we study a signal line which is a sandwich of Py inside two nonmagnetic metallic films. We find that the thickness and conductivity of the metal films can significantly alter the amount of absorption, at ferromagnetic resonance, between the symmetric and antisymmetric spin wave modes. The experimental results are supported by numerical calculations indicating the origin of the strength of the absorption.

Effects of adjusting the position of the magnetic layer in magnetic notch filters

We study small thin-layer magnetic notch filters which operate in the 5–40 GHz range. Past theoretical work has concentrated on a structure where the magnetic film was right next to one of the conductive films in a waveguide. Here we present a theoretical model, which investigates the properties of a waveguide with two dielectric films and one magnetic film placed between two outer conductive layers. The results show this more general structure produces a deeper attenuation and a narrower peak compared to the earlier structure. The additional attenuation varies from 0 to 30 dB/cm, depending on the thickness and position of the magnetic film. This article also examines the reflection of the guided waves as they enter the notch filter. The results from an effective medium calculation show that a signal experiences the largest return losses near the ferromagnetic resonance frequency of the magnetic film, with typical losses below −4 dB. The return loss can be reduced significantly if the linewidth in the fer...

Nonlinear amplification and mixing of spin waves in a microstrip geometry with metallic ferromagnets

We explore the nonlinear mixing and amplification of magnetic polariton modes in ultrasmall waveguides. Ultrasmall waveguide geometries can produce large oscillating microwave fields—up to about 500 Oe. Using these large fields, we examine nonlinear ferromagnetic dynamics in ribbons of Permalloy and Fe. In particular if two microwave signals at different frequencies are sent into the waveguide, we can increase the transmission of one wave by adding energy to the other wave. We also demonstrate the creation of new frequencies and the development of a comb of equally spaced frequencies. These experimental results are explained with perturbation theory and micromagnetics calculations.

On-wafer microwave signal-to-noise enhancer using NiFe films

This paper presents experimental results on a tunable microstrip signal-to-noise enhancer based on NiFe films. Structures involving the first- and second-order Suhl instabilities are compared. The enhancement factor is 10dB for a structure involving only the second order instability and an enhancement factor of 30dB is found for a structure where the first order instability is allowed.

Increasing Operational Frequency in Microwave Devices by Using [SmCo/NiFe] Multilayered Structures

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

Dynamic properties of arrays of ferromagnetic rectangular bars

Dynamic properties of arrays of rectangular bars were studied employing network analyzer ferromagnetic resonance and time-resolved magneto-optic Kerr effect (MOKE) measurements. The bars were patterned on top of coplanar waveguides and oriented with their long axis either parallel or perpendicular to the external magnetic field. Orientation of the bars parallel to the field results in an increase in the resonant frequency by up to ∼2GHz, as well as the linewidth broadening by 0.3–1GHz. The shift is shown to be in agreement with results expected from the difference of demagnetizing factors. The general behavior of the linewidth corresponds to calculations including shape anisotropy; however, the experimentally measured effect is much stronger than expected from theory. Fourier transforms of the time-resolved MOKE signal reveal the presence of several oscillatory modes, associated with the dynamics in the central part and at the borders of ferromagnetic elements.

Nonlinear Microwave Effects on Iron Based Microstrip Filter

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 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-mum-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