Temperature Dependence Of Ferromagnetic Resonance Research Articles

Magnetoelectric coupling in multiferroic Z-type hexaferrite revealed by electric-field-modulated magnetic resonance studies

Temperature dependence of ferromagnetic resonance (FMR) frequency fFMR was revealed in Z-type hexaferrite (BaxSr1−x)3Co2Fe24O41 using microwave spectroscopy in zero external magnetic field. A linear decrease in fFMR toward magnetic phase transition temperature Tc2 = 500 K was observed, implicating magnetic anisotropy decrease. Ferromagnetic resonance studies performed near 9 GHz with the magnetic field up to 10 kOe also confirmed FMR anomaly near 500 K, where the magnetic structure changes from conical to collinear. FMR spectra are tunable by external dc and ac (100 kHz) electric fields which allowed us to determine the value of magnetoelectric coefficient αE = 390 ps/m at 170 K. αE is at about 0.5 kOe one order of magnitude lower than the reported value at 10 K, because in our case the electric field was applied along c-axis, while the previously reported value was obtained with the field in hexagonal plane. Nevertheless, our αE is still one or even four orders of magnitude higher than in other “high-temperature” multiferroics.

Increased low-temperature damping in yttrium iron garnet thin films

We report measurements of the frequency and temperature dependence of ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film grown by off-axis sputtering. Although the FMR linewidth is narrow at room temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2) $\times 10^{-4}$), comparable to previous results for high-quality YIG films of similar thickness, the linewidth increases strongly at low temperatures, by a factor of almost 30. This increase cannot be explained as due to two-magnon scattering from defects at the sample interfaces. We argue that the increased low-temperature linewidth is due to impurity relaxation mechanisms that have been investigated previously in bulk YIG samples. We suggest that the low-temperature linewidth is a useful figure of merit to guide the optimization of thin-film growth protocols because it is a particularly sensitive indicator of impurities.

Temperature and Angular Dependence of Ferromagnetic Resonance (FMR) Signal of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> (LSMO) Thin Film Using FMR Technique

This research study was aimed at determining the temperature dependence of Ferromagnetic Resonance (FMR), the recorded signal versus angle and the magnetic property of the 15 uc thick La_0.7Sr_0.3MnO₃ (LSMO) thin film sample on a single crystalline SrTiO₃ (STO) substrate at 150 K and 9.75 GHz using ferromagnetic resonance technique. We observed from the Ferromagnetic Resonance (FMR) spectra at various temperatures (150, 200 and 250 K, respectively) that as the temperature increases, the FMR spectra shifts to higher fields and this might be as a result of transition into the ferromagnetic state. The recorded signal versus the angle showed an unusual phenomenon at all temperatures (150, 200 and 250 K, respectively) and this might be due to shape effects and other contributing factors such as misfit strain and crystal misfit in the LSMO thin film. The plot of resonance field versus the in-plane angle showed a spectrum which was sinusoidal-like in nature with maximum and minimum curvatures. The resonance position and the Full Width Half Maximum (FWHM) of the 15 uc thick LSMO thin film were 718.15 and 561.45 Oe, respectively. The 15 uc thick LSMO thin film displayed ferromagnetic resonance at 150, 200 and 250 K, respectively and this has been confirmed using the surface plot.

Dynamical effect in measurement of the exchange-bias field: A consequence of the slow-relaxer mechanism

We report on the temperature dependence of ferromagnetic resonance (FMR) measurements on NiFe/FeMn bilayer. This includes investigations about the angular distribution of the resonance, ${\text{H}}_{\text{R}}$, and that of the linewidth, $\ensuremath{\Delta}\text{H}$. By considering the domain-wall formation model, the exchange-bias field, ${\text{H}}_{\text{EB},\text{FMR}}$, is derived from the FMR measurements. The disagreements observed at low temperature between these values and the ones obtained from superconducting quantum interference device measurements, ${\text{H}}_{\text{EB},\text{SQUID}}$, are discussed. We demonstrate that the negative line shift and the maximum of the linewidth of the FMR line are both perfectly interpreted through the slow-relaxer mechanism. This enabled us to elucidate the intriguing question about the yielding to different values of the exchange-bias anisotropy by both techniques.

Temperature dependence of ferromagnetic resonance in permalloy/NiO exchange-biased films

The temperature dependencies of the ferromagnetic resonance (FMR) linewidth and the resonance field-shift have been investigated for NiO/NiFe exchange-biased bilayers from 78 K to 450 K. A broad maximum in the linewidth of 500 Oe, solely due to the exchange-bias, is observed at ≈150 K when the magnetic field is applied along the film plane. When the magnetic field is applied perpendicular to the film plane, the maximum in the linewidth is less pronounced and amounts to 100 Oe at the same temperature. Such a behavior of the FMR linewidth is accompanied with a monotonic increase in the negative resonance field-shift with decreasing temperature. Our results are compared with the previous experimental FMR and Brillouin light scattering data for various ferromagnetic/antiferromagnetic (FM/AF) structures, and suggest that spin dynamics (spin-wave damping and anomalous resonance field-shift) in the FM/AF structures can be described in a consistent way by a single mechanism of the so-called slow-relaxation.

Temperature dependence of ferromagnetic resonance of Al/Fe bilayers

In this work, we report the first results of a study of the dependence of ferromagnetic resonance (FMR) of Al/Fe bilayers. In-plane FMR field, H R, and linewidth, Δ H, has been obtained as a function of the azimuthal angle, ϕ H , Al layer thickness, t Al, and temperature, T. The dependence of H R and Δ H on ϕ H was interpreted in the framework of a model that includes cubic magnetocrystalline and out-of-plane uniaxial anisotropies, and in-plane dispersions of the cubic axes. Our study reveals the complexity of the relaxation mechanisms at the Al/Fe interface.

Temperature dependence of ferromagnetic resonance in granular Cu–Co alloy

Ferromagnetic resonance (FMR) spectra (derivatives of microwave power absorption) were measured in a granular, ribbon-shaped melt-spun Cu90Co10 alloy in a wide range of temperatures from 10 K up to room temperature. Prior to measurements the sample was annealed at 773 K for 1 h in order to create a well-developed granular structure. The results are interpreted using the Kittel FMR equations originally introduced for thin ferromagnetic films, as well as by using an Arrhenius-type exponential function for superparamagnetic relaxations. These results are also compared with the experimental data obtained from low-field susceptibility measurements in both, zero-field-cooling and field-cooling modes. It is shown that FMR spectroscopy is a useful tool for studying magnetic properties of granular magnets consisting of nanometer-scale single-domain particles, in particular, if the resonance spectra are measured in a wide range of temperatures, thus allowing for identification of the magnetic phases of the particles. The derived value of 10−13 s for the characteristic time of superparamagnetic relaxations is four orders of magnitude smaller than that commonly used while analyzing data yielded by just one measuring technique. The obtained results allowed us to estimate the first order constant of the magnetocrystalline anisotropy for fcc Co particles in the copper matrix K1=−4.2×106 erg/cm3.

Temperature dependence of ferromagnetic resonance as induced by NiO pinning layers

Ferromagnetic resonance (FMR) experiments have been conducted near 9.5 GHz on permalloy (Py) thin films which are components of spin valves and related structures. These so-called giant magnetoresistance structures often use antiferromagnetic NiO to achieve pinning of one magnetic layer. Magnetic anisotropies acting on these pinned layers were deduced by observing their resonances for fields perpendicular to and in the sample plane. We used data taken from 4 to 600 K to identify potential mechanisms of pinning, anisotropy, and linewidth. The anisotropic exchange pinning and an isotropic downward FMR shift vanish at a blocking temperature well below the bulk Neél temperature of NiO. The strong temperature dependencies of the isotropic shift and linewidth may reflect the presence of different spin pinning subsystems and the different time scales of the FMR and low frequency or static measurements.

Temperature-dependent FMR investigations on epitaxial Fe (001) films with different thicknesses

The temperature dependence of ferromagnetic resonance (FMR) spectra of single epitaxial (001) Fe films of different thicknesses ( d = 1.0, 2.0, 4.0, 20.0 nm) were examined in the range from 4 to 570 K. Two resonance lines were observed. The change in line position is essentially governed by the strong temperature dependence of the crystalline anisotropy constant K 1 which was found to be close to the value of bulk Fe. The linewidth of the observed resonances decreases roughly with the inverse power of temperature. The narrowing is attributed to the decrease of the crystalline anisotropy and of the magnetostriction.

The temperature dependence of ferromagnetic resonance in an uncompensated CaGe:YIG film

Using ferromagnetic resonance in Ca rich CaGe:YIG films, the anisotropy energy constants are determined by the best fit of resonance field data vs. angle. With decreasing temperature (294 to 180 K) the first-order cubic anisotropy constant K 1 increases nearly linearly, while the second-order constant K 2 increases dramatically. The uniaxial constant K u changes sign at about 240 K. When the sample is reduced in boiling FeCl 2, the linewidths are also reduced and the K u increases significantly while K 1 and K 2 decrease.

A contribution to the study of ferromagnetic resonance in manganese zinc ferrites

A study is made of the temperature dependence of ferromagnetic resonance in the 9300 Mc band on three samples of manganese zinc ferrite. The results are discussed from the point of view of the Tsuya model for the production of an additional internal field during ferromagnetic resonance.