Measurements of the Magnetic Susceptibility

In all these methods, one measures only one component of the magnetic susceptibility (the largest one for paramagnetic and the smallest for diamagnetic samples). The analysis is based on measuring the force on a sample placed in inhomogeneous magnetic fields  

If the material is placed in tubes with cylindrical cross section of area A = r n, (7.36) simplifies to  

In the Faraday balance, the entire tube is placed in an inhomogeneous magnetic field, which can be characterized by a constant gradient, VB, where Bj B2 = Bj - AB and B2 - Bj = In this case, the force reads as  

Schematics of the microbalances used to measure magnetic susceptibilities, (a) Gouy balance (b) Faraday balance.  

N 5 X 10 N. This corresponds to an effective mass of = 5 lOr kg = 5mg. To measure such small forces we need microbalance, or much larger gradient of magnetic induction. 

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About twenty years ago we reported on the di-isothiocyanato iron(II) complex of the tetradentate ligand tpa (tris(2-pyridylmethyl)amine) [7] (6). It was shown that this complex exhibits the spin crossover phenomenon with a critical temperature Tm of about 170 K. Several different solvated phases of the same system have since been characterized by Chansou et al. [8]. The unsolvated phase which can be isolated from an aqueous solution has been investigated by nuclear forward scattering (NFS), nuclear inelastic scattering (NIS) [9], extended x-ray absorption fine structure (EXAFS) spectroscopy, conventional Mossbauer spectroscopy, and by measurements of the magnetic susceptibility (SQUID) [10-13]. The various measurements consistently show that the transition is complete and abrupt and it exhibits a hysteresis loop between 102 and 110 K. 

Variable-temperature measurements of the magnetic susceptibility at 0.1 and 1.0 T between 2 and 290 K indicated temperature-independent diamagnetism 44). That is, flat % versus T curves, for both 3 (Xdiayrip(3) =-10.2 X lO emumor ) and 4 (Xdia/Tip(4) =-9.8 x 10 emu mol were obtained. By comparison these numbers for the... 

Ketonate complexes of Ru are reported in a number of papers. The parent complex [Ru(acac)3] has been subject to a polarized neutron diffraction study at 4.18 K, to powder neutron diffraction studies and to single-crystal structure determinations at 293 K, 92 K, and 10.5 K. The structure is disordered at all temperatures. Measurements of the magnetic susceptibilities (at 2.5 K and 300 K) have been made along different crystal axis directions, and the results analyzed. An investigation of the relationships between ionization potentials and half-wave potentials of a series of tris(/3-ketonate)Ru complexes has been reported, and the electrochemical properties of [Ru(acac)3] in chloroaluminate molten salt media have been reported. The reduced species [Ru(acac)3] can react with AICI4 reduction by bulk electrolysis of a small amount of [Ru-(acac)3] in the melt yields [RuClg]. ... 

We have described in some detail these two properties. Measurements of the magnetic susceptibility and of the electronic specific heat give very clear information, from N(pf), on the presence of an f narrow band. They will be discussed in more detail in Chap. D. 

From measurements of the magnetic susceptibilities of a large number of arsenic compounds it is found11 that combined arsenic has two... 

Measurements of the magnetic susceptibility (58) of the cobalt enzyme (Table 5) show that the metal ion is bound as high-spin Co (II). The intensity of the visible absorption makes an octahedral coordination, as well as tetragonal distortions thereof, very unlikely. In the combination with CN, the Co(II) enzyme exhibits the spectral features of tetrahedral model complexes with regard to intensity as well as structure both in the visible and the near-infrared wavelength regions (Fig. 8). The width of the near-infrared band (cf. 20) indicates that the deviation... 

Fig. 24. Temperature dependence of the thermal conductivity k for single-crystal samples of LaMnj Ga O3. The arrows mark or Tf obtained from measurement of the magnetic susceptibility, after Zhou et al. (2001a).

There has recently been invented an instrument for the determination of the amount of oxygen in a gas by measurement of the magnetic susceptibility of the gas. Oxygen is the only common gas that is strongly magnetic, and the magnetic susceptibility of a gas mixture is determined nearly entirely by the amount of oxygen in it. 

A new measurement of the magnetic susceptibility of UF3 (166) confirms that it obeys the Curie-Weiss relation over the temperature range 100-300 K and gives a Weiss constant of -12 K compared with earlier values of -98 K (142), -32.2 K (167), and -110 K (168). A lower effective magnetic moment is reported, 3.30 ib, compared with 3.66 (142), 3.50 (167) and 3.62 (168). These differences very probably reflect differences in the purity of the UF3 used (142, 167). 

The authors are grateful to Prof. R. MacCrone for the measurement of the magnetic susceptibility and Lydle Valade for assistance with the conductivity measurements. We thank the Office of Naval Research for financial support of this research. 

The paramagnetism of the conduction electrons, not observable by ESR, can however be detected by a measurement of the magnetic susceptibility. In the region of metalhc conductivity, one observes in the contribution of the conduction electrons a nearly temperature-independent Pauli susceptibility, well known from metals. In those crystals which undergo a Peierls transition and become semiconductors or insulators at low temperatures, the Pauli susceptibility is transformed into a Curie-law behaviour. The susceptibility then increases with further decreasing tern-... 

Figure 9.16a shows the temperature dependence of the energy gap, A(T) (solid curve), as obtained from a measurement of the magnetic susceptibility of the conduction electrons (see Sect 9.6.4 and [24]). With this information, the experimental temperature dependence a(1) was fitted to Eq. (9.14) (Fig. 9.17). The fit shows that the essential characteristics of a (7) from room temperature down to about 50 K, with a variation of more than eight orders of magnitude, are correctly described by this equation. It is thus justified to use Eq. (9.14) alone for the determination of the energy gap A(7) and the constant C. Figure 9.16a shows the energy gap A(T) (dashed curve), as determined directly from the conductivity a(T) (Fig. 1.13) using Eq. (9.14). From this fit, the constant C is also obtained (Table 9.3).

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