MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Electronic and Magnetic Measurements 51
Above the Curie temperature the molecular field model gives the Curie-
Weiss law for the zero-field susceptibility χ mol
2 2
NAμ
B gJJ ( + 1)
=
3k
T − Θ , where ΘP is
B P
the paramagnetic Curie temperature. In the Curie-Weiss molecular field
model Θ P = T C . Experimentally, for reasons discussed below, the experimental
value of Θ P is usually a slightly larger than the true critical temperature T C .
In a field, this susceptibility is slightly less than linear (χ 3 < 0), like it is for
paramagnetic moments, due to saturation. The calculated inverse
susceptibility, 1/χ = H/M, is shown in Figure 3-6 for SrRuO 3 . The 1/χ = 0
intercept of the extrapolation of 1/χ vs. T is the paramagnetic Curie
temperature Θ P .
Below T C the mean field magnetization decreases exponentially slowly as
the temperature is raised from T = 0 K, as shown in Figure 3-7. The zero field
magnetization decreases to zero at the ferromagnetic Curie temperature T C .
Also at low temperatures, the mean field magnetic susceptibility is very
small, i.e. the application of a magnetic field increases the calculated
magnetization only slightly (Figure 3-7).