Magnetic susceptibility Curie temperature

Bae] Temperature dependence of magnetic susceptibility Curie temperature... 

One of the important characteristics of ferroelectrics is that the dielectric constant obeys the Curie- Weiss law (equation 6.48), similar to the equation relating magnetic susceptibility with temperature in ferromagnetic materials. In Fig. 6.55 the temperature variation of dielectric constant of a single crystal of BaTiOj is shown to illustrate the behaviour. Above 393 K, BaTiOj becomes paraelectric (dipoles are randomized). Polycrystalline samples show less-marked changes at the transition temperature. 

Fig. 11.57 Plot of the reciprocal of magnetic susceptibility vs. temperature for three, magnetic behaviors (a) itie Curie law (b) the Curie-Weiss law for a ferromagnetic substance with Curie temperature, Tc, (c) the Curie-Weiss law for an antiferromagnetic, substance with Neel temperature, T. ...

Fig. 11.59 Variation of magnetic susceptibility with temperature for diamagnetic, paramagnetic, ferromagnetic, and antiferromagnetic substances. Transitions to paramagnetic behavior for ferromagnetic and antiferromagnetic substances occur at the Curie (Tc) and Neel (TN) temperatures, respectively.

The magnetic susceptibility versus temperature behavior is typically interpreted using three types of plots. One is the so-called Curie-Weiss plot of 1/x versus T (Fig. 2). The Brillouin form of magnetization given earlier reduces to a simple form when H T in energy terms the Curie law (Equation (3)), in... 

For a range of related materials the concentration dependence of the magnetization M, Curie temperature Tc and initial susceptibility xo takes the form... 

Saturation magnetization M0, Curie temperature Tc, high-field susceptibility Xht anc the pressure dependences of M0 and Tc for Fej alloys (Beille et al. 1979). 

EuCuBi is antiferromagnetic at low temperature (Tn = 18K) and follows the Curie-Weiss law at high temperatures, with an effective magnetic moment (/Xeff = 7.65 /xb) somewhat smaller than that expected for Eu + (7.94 /xb) (Tomuschat and Schuster, 1981, 1984). The electrical resistivity of a pressed pellet of YbCuBi shows metallic behaviour (psoo K = 0.3 mf2 cm) but displays a kink around the structural phase transition at 375 K (Merlo et al., 1995). The magnetic susceptibility is temperature-independent (1.6 x 10 " emu/mol) with a Curie tail at low temperature attributed to the presence of less than 2% paramagnetic Yb " " impurities (Kaczorowski et al., 1999). 

Equation (A2.5.20) is the Curie-Weiss law, and the temperature at which the magnetic susceptibility becomes infinite, is the Curie temperature. Below this temperature the substance shows spontaneous magnetization and is ferromagnetic. Nonnally the Curie temperature lies between 1 and 10 K. However, typical ferromagnetic materials like iron have very much larger values for quantum-mechanical reasons that will not be pursued here. 

At room temperature, osmium hexafluoride yields a blue material of approximate composition CgOsFg (B22). Its magnetic susceptibility obeys the Curie-Weiss law, with a magnetic moment, /lefi = 3.5 BM,... 

Above a critical temperature Tc, the Curie temperature, a ferromagnetic material becomes paramagnetic, since thermal motion inhibits the parallel orientation of the magnetic moments. The susceptibility then follows the Curie-Weiss law with a positive value of the Weiss constant, 0 > 0 (Fig. 19.6). 

At ordinary temperatures die magnetic susceptibility is given approximate This relation was determined experimentally by Piene Curie. Preach physicist... 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

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