Dynamic susceptibility data

Magnetic Granulometry from the Dynamic Susceptibility Data... 

Complex dielectric susceptibility data such as those in Figure 15.6 provide a detailed view of the dynamics of polar nanodomains in rls. They define relaxation frequencies, /, corresponding to the e (T) peak temperatures Tm, characteristic relaxation times, r = 1/tu (where uj = 2nf is the angular frequency), and a measure of the interaction among nanodomains as represented by the deviation of the relaxation process from a Debye relaxation. Analysis of data on pmn and other rls clearly shows that their dipolar relaxations cannot be described by a single relaxation time represented by the Debye expression... 

The theory was tested with the aid of an ample data array on low-frequency magnetic spectra of solid Co-Cu nanoparticle systems. In doing so, we combined it with the two most popular volume distribution functions. When the linear and cubic dynamic susceptibilities are taken into account simultaneously, the fitting procedure yields a unique set of magnetic and statistical parameters and enables us to conclude the best appropriate form of the model distribution function (histogram). For the case under study it is the lognormal distribution. 

The study that we describe below was inspired by our work on fitting the dynamic susceptibilities measurements for real assemblies of fine particles. Those data typically describe polydisperse systems in the low-frequency bandwidth a>/2% = 1 — 103 Hz. As To 10 s or smaller, then, using formula (4.132) for estimations, one concludes that the frequency interval mentioned becomes a dispersion range for the interwell (superparamagnetic) mode at coto< ct > 1, that is, a > 10. For temperatures up to 300 K, this condition holds for quite a number of nanomagnetic systems. 

Postprocessing of Dynamic Susceptibility Contrast-Enhanced Data 105... 

Experimental NMR data are typically measured in response to one or more excitation pulses as a function of the time following the last pulse. From a general point of view, spectroscopy can be treated as a particular application of nonlinear system analysis [Bogl, Deul, Marl, Schl]. One-, two-, and multi-dimensional impulse-response functions are defined within this framework. They characterize the linear and nonlinear properties of the sample (and the measurement apparatus), which is simply referred to as the system. The impulse-response functions determine how the excitation signal is transformed into the response signal. A nonlinear system executes a nonlinear transformation of the input function to produce the output function. Here the parameter of the function, for instance the time, is preserved. In comparison to this, the Fourier transformation is a linear transformation of a function, where the parameter itself is changed. For instance, time is converted to frequency. The Fourier transforms of the impulse-response functions are known to the spectroscopist as spectra, to the system analyst as transfer functions, and to the physicist as dynamic susceptibilities. 

The above expressions show that the key analysis of a single-chain magnet system is the comparison between susceptibility and relaxation data. In fact, the observation of an activated relaxation time is not characteristic of SCM behavior (a similar behavior is obtained for other systems like SMMs) and a discussion based only on the dynamic data remains highly ambiguous. The situation is different if the thermodynamic and dynamic properties are compared as A can be deduced from susceptibility data and then considered to... 

An attempt to explain experimental data for the neutron scattering function S(o), T) of the y- and a-phases of metallic Ce on the basis of CF and spin-orbit effects (without taking into account the interaction between 4f and conduction electrons), is due to Orlov (1988). The effect of spin-orbit splitting on the dynamic susceptibility of VF systems within the framework of the NCA has been considered by Cox et al. (1986). 

In Part I- F the magnetic properties of metal-ammonia solutions were listed. As we have seen, the obseiwed magnetic properties consisted of results of total susceptibility measurements, spin susceptibility measurements using electron spin resonance techniques, dynamic features of electron spin resonance involving measurements on the relaxation times, and nuclear resonance studies. We shall first take up the explanation of the susceptibility data using the cavity, cluster, and unified models and subsequently consider the interpretation of the results of resonance studies. 

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