Susceptibility measurements

Let s consider an SMM, which is magnetized to a magnetization, M0, with a polarizing magnetic field, H. After (fast) removal of the field, the magnetization will decay exponentially with a single characteristic relaxation time (t)  

In real systems, a distribution in the characteristic time may lead to a stretched exponential decay. In the thermally activated regime where the relaxation of the magnetization is due to the Orbach mechanism, the temperature dependence of the relaxation time may be described by an Arrhenius law of the form  

From x = x + ix it is straightforward to obtain the expressions of the real and imaginary components of the ac susceptibility [7] 

For cot = 1, x and x display, respectively, an inflection point and maximum reaching values of (xT + Xs)/1 and Xt-XsI/ = max[ ]. Therefore, the temperature dependence of the relaxation time, t T), is conveniently obtained from ac susceptibility measurements when r = (max[ ]) 1 (in this formula, (maxl ]) designates the angular frequency of the / peak maxima). It is worth noting that the r = (max[ ]) 1 relation is always valid when x is measured as a function of the ac frequency at fixed temperatures as Xt and Xs are constants. On the other hand, if x is measured at fixed ac frequency as a function of the temperature, the r = (max[ (r)]) 1 equality is not preserved when x- and Xs are temperature dependent. 

In real systems, there will always be a distribution of the relaxation time meaning that Equation 5.3 should more adequately be written as given in Ref. [8] (generalized Debye model)  

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Most important is the following Fig. 7c shows that the segregation can be detected also from that side where it does not extent to the surface. This confirms that the material is transparent for this kind of susceptibility measurements. That means, that also segregations can be detected, which are in the volume and do not extent to the surface. 

Co(II), Ni(n), Cu(n), and Zn(II) complexes of Schiff bases derived from 4-aryl-2-aminothiazoles and salicylaldehyde have been prepared, and structure 276 (Scheme 170) was established by magnetic susceptibility measurements and by infrared, electronic, and mass spectra (512). 

However, magnetic-susceptibility measurements on other graphite-metal chlorides indicated that electron transfer is insufficient to account for reduction of the cation... 

Magnetic-susceptibility measurements showed the presence of UF4 in heated samples. Ebert et al. (E14) reported a nominal stoichiometry CisUFg, magnetic-susceptibility measurements indicating partial reduction at room temperature, with 10% of the uranium species present as U(IV). Wide-line NMR demonstrated the presence of both U(VI) and U(IV). 

The system Y(Rh xRUx)4B4(LuRu4B4 type, x > 0.15, x-ray diffraction, electron spcctropy, ac-magnetic susceptibility measurements) is similar. The abrupt disap-... 

Following the completion of the sintering study, a study was conducted to demonstrate that 663 K, the temperature at which all magnetic susceptibility measurements were taken, was indeed greater than Tq, . As discussed in the theory section, measurements were made at several temperatures until it was determined that plots of M/Mg versus H/T collapsed onto a single curve. It is clear from Figure 4 that Tqj, must be less than 450 K. That is, for any temperature above 450 K the average particle size was measured to be nearly 200 A in diameter. For smaller particles, Tq, will of course be an even lower temperature. This proves that all measurements made at 663 K were indeed accurate. 

It is thus evident that, in order to interpret the results obtained by one of the relaxation methods, a thorough investigation of the unperturbed equilibrium properties is required. In general, solution magnetic susceptibilities measured by the NMR method of Evans [83, 84] are used to this end, the equilibrium constant for the equilibrium in Eq. (37) being determined by ... 

J-mph denoting the four-dentate NjOj Jager-type ligand 4-methyl-l,2-phenylenebis(diacetylacetaldimine) [163]. Based on magnetic susceptibility measurements between 80 and 320 K, the transition is centred at 7[ — 212 K and is incomplete at both high and low temperatures. In order to reproduce the Mossbauer spectra between 84 and 319 K, three models of increasing sophistication were employed [164] ... 

Fe(6-Mepy)2(py)tren] (004)2 Doped in PSS. Magnetic susceptibilities measured for a microcrystalline sample of the complex produce a magnetic moment value = 0.36 pg at 10 K and 0.61 pg at 150 K, followed by a gradual increase to Peff = 2.80 pe at 311 K [138]. Thus 26% of the complexes are in the HS state at 300 K if a magnetic moment of 5.1 Pe is assumed for the pure HS compound. On the other hand, the complex doped into a polystyrene sulfonate (PSS) film does not provide any evidence for a thermal population of the HS state up to 340 K as demonstrated by variable-temperature UV-VIS and Mossbauer spectra. In fact, all the complexes doped into the PSS film are in the LS state at temperatures below 340 K. However, if irradiated by a single pulse of a Q-switched Nd/YAG laser (532 mp), the complex is excited from the LS ground state to the HS J2 states via an intermediate MLCT state and the metal states. The subsequent back relaxation from the excited T2 state to the... 

A careful magnetic and optical study of AgMn04 has been made by Sperka and Fritzer [45]. They find the Ag(I)-Mn(VII) MMCT transition at about 10000 cm (see Fig. 6). The ground state Ag(I)Mn(VII)04 is confirmed by magnetic susceptibility measurements. 

The W(IV) compounds W(Et2C c)4 (14) and [(CU.2)ndtc] (15) are characterised only by analytical data and magnetic susceptibility measurements. They are considered to be paramagnetic with moments of about 1.0 BM, which is in contrast with the diamagnetism of W(R2[Pg.94]

The reports about the crystal structure of Mn(Et2cftc)2, determined by means of X-ray powder diagrams are contradictory. According to Fackler and Holah (18) this compound is isomorphous with Cu(Et2rftc)2, but Lahiry and Anand (44) state the complex to be isostructural with Ni(Et2 tc)2- EPR data (g = 1.92 and g = 4.11) and magnetic susceptibility measurements (4.1 BM at room temperature) show the compound to be the first Mn(II) complex with a quartet ground state (44). 

In this study, we extend the range of inorganic materials produced from polymeric precursors to include copper composites. Soluble complexes between poly(2-vinylpyridine) (P2VPy) and cupric chloride were prepared in a mixed solvent of 95% methanol 5% water. Pyrolysis of the isolated complexes results in the formation of carbonaceous composites of copper. The decomposition mechanism of the complexes was studied by optical, infrared, x-ray photoelectron and pyrolysis mass spectroscopy as well as thermogravimetric analysis and magnetic susceptibility measurements. 

A hysteresis cycle in the molar susceptibility measurements has been observed for [Ni2(Medpt)2(N3)2(/r-N3)2] (883). This has been ascribed to a phase transition caused by an asymmetrization process of the rhombus-like centrosymmetric [Ni-(N3)2-Ni] core that occurs with falling temperature. The asymmetrization transition can be explained in terms of a second-order Jahn-Teller distortion, taking into account the local symmetry of the dinuclear [Ni-(N3)2-Ni] entity (D2h, rhombic symmetry) before the arrangement.2128... 

That the Pd-H system is composed of the units Pd and PdH has been suggested by Linde and Borelius on the basis of experiments on the behavior of the electrical resistance. Oxley7 has also suggested on the basis of susceptibility measurements that the hydrogen is in intimate association with the palladium. The study of the Pd-H system in this laboratory has been extended in other directions and the results will be reported soon. 

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