Ferromagnetic Resonance Behavior Research Articles

Ferromagnetic resonance and superparamagnetic behavior of iron oxide nanoparticles injected in porous anodic alumina

Iron oxide nanoparticles with diameter around 10nm were produced and injected in 60μm thick anodic alumina membranes with pore diameters of 20 and 100nm. The structure, magnetic properties, and the ferromagnetic resonance frequency of the nanoparticles before and after injection into the columnar arrays were measured as a function of the out-of-plane applied field. The effect of dipolar interactions and clustering mechanisms of the injected nanoparticles on the static and radio frequency magnetic response is discussed.

Spin waves in ferromagnetic/antiferrmagnetic bilayers under the stress field

Using a method of free energy minimization, the spin wave, namely the ferromagnetic resonance, of ferromagnetic (FM)/antiferromagnetic (AFM) bilayers under the stress field has been investigated. The thin FM film is taken to be a single crystal with cubic or uniaxial magnetocrystalline anisotropy, while the thickness of AFM layer is semi-infinite and has single uniaxial magnetocrystalline anisotropy. Numerical calculation shows that stress field and the interface coupling strength will affect the behavior of FM resonance only under low magnetic field, and there are two branches of FMR modes at the critical field, which distinguishes between the weak and strong external field. The critical field depends on the direction of stress field. On the other hand, the change of the direction of the stress field can weakly affect magnetocrystalline anisotropies axis of FM layer.

Possible existence of a new type of left-handed materials in coupled ferromagnetic bilayer films

On the basis of Landau–Lifshitz–Gilbert (LLG) equation, an anomalous ferromagnetic resonance behavior is demonstrated in detail. Coupling between the magnetic moments produces a 3 π/2 phase delay for one of the moments ferromagnetic resonance unusually, thus leads the sign of magnetic susceptibility χ ˜ = χ ′ - j χ ″ to be opposite to that induced by the usual ferromagnetic resonance. Consequently, a left-handed material (LHM) may be formed near the low-frequency side of the resonance. Particularly, a LHM with negative value of real part of permeability only is predicted.

Ferromagnetic resonance in amorphous nanoparticles

We present the results of ferromagnetic resonance (FMR) measurements on noninteracting amorphous nanoparticle systems (Co 0.25Ni 0.75) 65B 35 (CNB2) and (Fe 0.25Ni 0.75) 50B 50 (FNB2) in the temperature range 10–300 K. The high-temperature results show symmetric lineshapes that indicate a low value of effective anisotropy. When cooling the linewidth increases and the lineshapes lose their symmetric shape. The lineshape can be interpreted as due to slightly elongated particles. In CNB2, we observe a sharp intensity maximum at T=60 K, followed by a linewidth maximum and resonance field minimum at T=50 K. The same tendency is observed in FNB2, with an intensity maximum near T∼40 K, with an increment in the linewidth and simultaneous decrease of the resonance field down to the lowest temperature, T=10 K. Previous magnetization measurements on these systems indicate large surface effects in the same temperature region of the observed anomalies. This picture, together with simulations, permits us to explain the FMR behaviour.

Magnetic properties of metallic ferromagnetic nanoparticle composites

Magnetic properties of nanoparticle composites, consisting of aligned ferromagnetic nanoparticles embedded in a nonmagnetic matrix, have been determined using a model based on phenomenological approaches. Input materials parameters for this model include the saturation magnetization (Ms), the crystal anisotropy field (Hk), a damping parameter (α) that describes the magnetic losses in the particles, and the conductivity (σ) of the particles; all particles are assumed to have identical properties. Control of the physical characteristics of the composite system—such as the particle size, shape, volume fraction, and orientation—is necessary in order to achieve optimal magnetic properties (e.g., the magnetic permeability) at GHz frequencies. The degree to which the physical attributes need to be controlled has been determined by analysis of the ferromagnetic resonance (FMR) and eddy current losses at varying particle volume fractions. Composites with approximately spherical particles with radii smaller than 100 nm (for the materials parameters chosen here), packed to achieve a thin film geometry (with the easy magnetization axes of all particles aligned parallel to each other and to the surface of the thin film) are expected to have low eddy current losses, and optimal magnetic permeability and FMR behavior.

Structure and magnetic properties of yttrium–iron–garnet thin films prepared by laser deposition

We report on a study of thin (500–4000 Å) and ultrathin (100–500 Å) yttrium–iron–garnet (YIG) films deposited onto amorphous quartz substrates by the pulsed laser deposition technique. The growth conditions of well-formed polycrystalline films have been determined. The crystalline structure and the magnetic behavior of the films are strongly influenced by the processes occurring on the film–substrate interface. Primarily, a strain due to the difference in thermal expansion coefficients of the film and substrate induces a uniaxial anisotropy. Another source of strain are lattice distortions due to oxygen vacancies. The results obtained from x-ray diffraction analysis, magneto-optical, superconducting quantum interference device, vibrating sample magnetometer, and ferromagnetic resonance (FMR) measurements indicate that films thicker than 200 Å can be approximated by a two-layer model. One of the layers with a highly distorted structure and low magnetization is located near the surface. The other one, the upper layer, can be estimated as an almost perfectly formed YIG. Their relative thickness determines the magnetic and FMR behavior of the samples. An equilibrium direction of the magnetization along the film normal has been found to occur in the ultrathin films with the lowest magnetization where the perpendicular anisotropy energy exceeds the dipolar energy.

Dielectric unusual behaviour of Sn/Nb substituted Mn-Zn ferrites

Dielectric constant ( ε) of Sn +4/Nb +5 doped Mn-Zn ferrites has been measured as a function of dopant concentration, frequency and temperature. At intermediate concentrations of dopant, an unusual behaviour of dielectric dispersion has been observed due to the occurence of dimensional resonance and thus the interesting results are obtained in the study of variation of ε with frequency. For these specimens, in addition to the usual dispersion of ε, an increase of ε with frequency is observed at two regions in the plot of log ε versus log f in support of occurence of dimensional resonance and ferromagnetic resonance behaviour. Studies of dielectric constant and dielectric loss with the variation of temperature have also been carried out to know the above said behaviour beyond magnetic Curie temperature. Results are explained on the basis of correlation between conductivity and dielectric constant, space charge polarisation, grain structure and additional phase formation.

Ferromagnetic resonance behavior of evaporated Gd-Fe alloy films

The bulk and local magnetic properties have been investigated for evaporated Gd-Fe alloy films. The origin of the multiresonance fields of amorphous Gd-Fe alloy films was speculated to be due to several compositionally different short-range-ordered structures. These results yield the locally different magnetic properties, such as the Curie temperatures, magnetizations, g values, and anisotropy field difference. The magnetization of the annealed alloy film increase mainly due to the ferromagnetically ordered α-Fe and α-Gd precipitates.

Crystallization and ferromagnetic resonance behavior of evaporated Gd-Fe alloy films

The composition and temperature dependence of the ferromagnetic resonance, as-deposited structures, and in situ crystallization behavior were investigated for evaporated Gd-Fe alloy films. The origin of multiple ferromagnetic resonance peaks in the amorphous alloy film was speculated to be due to compositionally different short-range ordered structures. The composition dependence of the structural variations in the as-deposited alloy films were consistent with the two sphere size hard sphere model. The in situ crystallization reactions of Gd-Fe alloy films were characterized by three separate reaction stages.

Ferromagnetic resonance in nickel around the curie temperature

The ferromagnetic resonance behaviour of nickel up to and above T c is investigated. It is shown that up to the Curie point, which is 357.8°C, the resonance can be described by the Gilbert equation with the parameters g = 2.20 ±0.02 and λ = (4.0±0.5) × 10 9 s −1. Above T c , however, it is an open question if the Gilbert equation describes the resonance adequately. No sign of a decreasing linewidth above 365°C is seen. On the contrary, the resonance broadens rapidly and fades away. The experiment is performed in a new way with the cavity kept at room temperature and the temperature of the sample is monitored during the run of the spectrum.

Ferromagnetic resonance in metallic multilayers. II. Numerical example and semiquantitative model

In the preceding paper, we have presented a method for analyzing the ferromagnetic resonance behavior of multilayer films. We present first the results for a relatively simple case. Then, a simple model is presented which yields the major features of the results of the rigorous calculation. With this model, it is possible to predict what will happen in a given situation and to develop an image of the internal magnetizations during resonance.

Magnon Analysis of Ferromagnetic Resonance in a Planer Ferrite, Zn2Y

The low power ferromagnetic resonance behavior at room temperature was measured on a magnetically anisotropic material, Zn 2 Y , with the object of studying relaxation processes on the basis of magnon manifold. The line-width of monocrystalline Zn 2 Y under a uniform mode resonance condition exhibits four kinds of maxima with increasing angle θ H of the applied d c field with respect to the crystallographic c axis. The first maximum is at θ H =0° and is small. The second maximum is the largest and extends over the entire region of θ H . The third and fourth maxima are small and attend on the larger angular tail of the second maximum. It may be concluded that the second maximum is due to the two-magnon decay of the uniform mode and the third due to the three-magnon decay of the uniform mode.

Ferromagnetic Resonance of Single-Crystal Gadolinium

Gadolinium metal is a system of relative simplicity as far as exchange interactions and ionic states are concerned. The 8S7/2 state of Gd3+ is consistent with the observed 7μb/atom and the moment contributing f electrons are most likely exchange coupled via conduction electrons. The present work concerns the measurement of the ferromagnetic resonance behavior of a single crystal at frequencies of 21 and 35 Gc/sec and at temperatures from above the Curie point (20°C) to 4.2°K. The resonance absorptions are well defined at both frequencies and at all temperatures for most crystal orientations. The minimum linewidth observed is about 400 Oe but the line shape and width degrade when the applied field departs from the easy axis, particularly at the lower frequency and at low temperatures. Strong, well-defined domain wall resonances are also frequently observed. The deduced magnetocrystalline anisotropy energy is accurately described by the standard uniaxial expansion EA = K1 sin2θ+K2 sin4θ+⋯, about the hexagonal axis. The anisotropy constants derived from the resonance data agree reasonably well with those measured by Graham1 using static torque methods. The samples used in these experiments are from the same source.2 The demagnetization fields at the surface of the coin-shaped sample are measured directly from the shift in the resonance field of a small chip of the free radical DPPH in intimate contact with the sample surface.3 The corresponding demagnetization factors lie between that calculated by Schlömann4 for a uniformly magnetized right cylinder (an accurate description of our sample shape) and that calculated for an oblate spheroid of the same axial ratio, tending toward the latter at low temperatures. Using the magnetization measurements of Graham (as a function of temperature and applied field) we find that the spectroscopic splitting factor, g, is 2.00±0.02 below 0°C, changing smoothly to 1.94±0.02 at 28°C in the paramagnetic region. This latter values agrees well with those reported by Kip5 and by Popplewell and Tebble.6 The g value at low temperatures, also deduced from the resonance data, gives better (but still not exact) agreement between the directly measured saturation magnetization and that implied by the 8S7/2 ionic state.