Asymptotic Curie temperatur

From an X-ray powder diffraction analysis, Felner (1973) reported the existence of HoAu Sij with the ordered ThCr2Si2-type of structure (14/mmm, a = 4.224, c = 10.12) sample preparation as for LaAu2Si2. Magnetic ordering (Ferromagnetic ) was observed at = 14.8 K the asymptotic Curie temperature was 0 = —2.1 K =10.6, tB-... 

Fig. 31. Magnetic phase diagram of the amorphous Gd, Al system. The freezing temperatures, ferromagnetic Curie temperatures and asymptotic Curie temperatures are indicated by means of 7, 7 and 0, respectively (after McGuire et al., 1978).

RKKY-type analysis of the conduction electron polarization Each time when the hyperfine fields at different sites in the same intermetallic compound were available-as for the Al sites in RjAlu in an NMR analysis by van Diepen et al. (1969)-or when the hyperfine fields and asymptotic paramagnetic Curie temperatures 0p could be correlated, or when the conduction electron concentration could be varied in pseudobinary intermetallic compounds, the RKKY model [as introduced by Jaccarino (1961) for the discussion of A1 NMR in RAI2] was the favourite framework for the NMR spectroscopists. For eq. (10b), is calculated as... 

The distance between neighboring chains L has been evaluated from the experimental EISF, and r and t from the experimental asymptotic values of HWHM. Figure 32a shows that L increases strongly from 1 up to 4.8 A with temperature while the jump parameter r varies only slightly (between 0,8 and 1.6 A). At 340 K the r and L values are nearly the same indicating that at the onset of the Curie transition all the free volume available is occupied by the jump. 

At the Curie point, the Weiss theory predicts that for T > Te, in the absence of an external field, the spin order vanishes completely. Actually there is considerable short-range order just above Te, as has been verified by neutron diffraction experiments (405,675). It is the problem of short-range order that is tackled by the more exact quantum statistics mentioned in connection with equation 94. At very high temperatures (T Te), there is no short-range order, and the experimental curve approaches the Curie-Weiss curve asymptotically. Theory shows that the possibility of short-range ordering lowers the... 

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