We come now to the determination of the class of materials whose magnetic properties may influence the Casimir force. It is common knowledge that all materials possess diamag- netic polarization, i.e., they are magnetized in direction opposite to the applied magnetic field. For all substances the magnetic permeability is represented in the form µ ( iξ ) = 1 + 4 πχ ( iξ ) , (6) where χ ( iξ ) is the magnetic susceptibility calculated along the imaginary frequency axis. The magnitude of χ ( iξ ) is a monotonously decreasing function of ξ . For diamagnets the diamagnetic polarization determines their magnetic properties so that [35–37] χ (0) < 0, µ (0) < 1 and | µ (0) − 1 | ∼ 10 − $^{5}$. From this it follows that magnetic properties of diamagnets cannot influence the Casimir force and one can put µ$_{l}$ = 1, l = 0 , 1 , 2 , . . . in computations using Eqs. (1) and (5). Typical diamagnets are such materials as Au, Si, Cu and Ag. It is important that Au, Si and Cu were used in experiments on measuring the Casimir force (see, e.g., papers [12, 30, 31, 42–46] and review of all related experiments [47]). Thus, it is justified to omit magnetic properties of these materials when comparing the experimental data with theory. Materials possessing paramagnetic polarization are magnetized in the direction of an applied magnetic field. For paramagnets in the broad sense χ (0) > 0 and µ (0) > 1 and no additional conditions on the character of the magnetic permeability apply [37]. Paramagnetic effects, if they are present, overpower the diamagnetic ones and determine the type of the material. Paramagnets may consist of microparticles which are paramagnetic magnetizable but have no intrinsic magnetic moment (the Van Vleck polarization paramagnetism [48]). The respective χ (0) is, however, negligibly small. Because of this the magnetic properties of Van Vleck paramagnets do not influence the Casimir force. Paramagnets may also consist of microparticles possessing an intrinsic (permanent) mag- netic moment (the orientational paramagnetism [35–37, 48]). In the narrow sense, magnetic materials with χ (0) > 0 are called paramagnets if the interaction of magnetic moments of their constituent particles is negligibly small. At sufficiently high temperature all paramag- nets are in fact paramagnets in the narrow sense. Their magnetic susceptibility varies from about 10 − 7 to about 10 − $^{4}$. When temperature decreases, there occurs a magnetic phase transition [49–51]. It happens at some critical temperature T$_{cr}$ specific for each material (for different materials T$_{cr}$ may vary [35–37, 49–51] from a few K to more than thousand K). 7