Magnetic transitions temperature

Cp.m = aT3 (antiferromagnetic crystals below the magnetic transition temperature if it occurs at low T (4.8)... 

The Mossbauer eflFect can also be used to measure the magnetic transition temperatures of magnetic materials. In fact, it has some advantages over conventional techniques since no external magnetic field is required for the measurement and one thereby avoids the usual problem of extrapolating to zero Hext- Three techniques are often used to measure magnetic transition temperatures. 

One can measure H as a function of temperature to see where Hx vanishes. If one assumes Hx is proportional to the magnetization, one can fit a Brillouin function through the data and extrapolate to zero Hx to get the magnetic transition temperature. As an example, the Neel temperature of -Fe203 has been determined by this technique [see Figure 1 of Ref. 12]. 

If one plots the area under the absorption curve as a function of temperature for a relatively thick absorber, a sharp discontinuity in the curve will be observed at the magnetic transition temperature—see, for example. Figure 11 of Ref. 35. 

Fig. 16. Anisotropic thermal expansion of GdAg2 measured by x-ray powder diffraction (this work). The lines represent the extrapolation of the lattice contribution from the paramagnetic range by fitting Debye functions. The arrows indicate the different magnetic transition temperatures (see text).

Cp - ml3 antiferromagnetic crystals below the magnetic transition temperature... 

FIGURE 18 Thermoelectric power Sq for RNi2B2C (R = Dy, Tb, Gd) measured perpendicular to the c-axis. The arrows indicate superconducting and different magnetic transition temperatures that are described in more detail in Sections 4.6, 4.7 (where Twfm>s used instead of Twf)> and 4.8 (after Hennings et al., 2002). 

Figure 2. Mossbauer spectra of Fe7S8 above the magnetic transition temperature. Continuous line is the least-square fit to the spectra.

Cubic-lattice constant, A. Magnetic transition temperature, °C. Magnetization, Bohr magnetons per molecule, 0°K. 

If, in a Mossbauer experiment, the relative transmissions at two velocities, v+ and v (where v+ = -v ) are measured in a temperature scan characteristic thermal-scanning curves are obtained like those in Fig. 3.42, which can be very useful for the determination of magnetic-transition temperatures under pressure/... 

Blaine and Fair (55) determined new estimates for the true magnetic transition temperatures of the ICTA Certified Magnetic Reference Materials GM761, using a six-point calibration method. The results of the magnetic transition temperatures obtained are presented in Table 3.2. Experimental measurement precision varied from 0.81°C for nickel to 3.2°C for Permanorm 3. The narrowest magnetic transition temperature was 3.0°C for nickel, whereas the widest was 13.1°C for Permanorm 3. A pooled standard deviation of 2.0°C could be calculated from these data. The experi-... 

Table 3.2. Observed Magnetic Transition Temperatures for Magnetic Standards GM 761 (55)...

Fig. 10. (a) Total specific heat of CeGa2 at the magnetic transition temperature, is ferromagnetic while 2, 3 and 4 denote the antiferromagnetic transitions, (b) Detailed structure at around 10 K, after Takahashi et al. (1988). 

Fig. 66. Temperature dependent resistivity for Gd2XC (X = Cl, Br, I) the magnetic transition temperatures are indicated by arrows.

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