MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

48 Chapter 3
Susceptibility (emu/G mol)
4.0 10 -2
3.5 10 -2
3.0 10 -2
2.5 10 -2
2.0 10 -2
1.5 10 -2
1.0 10 -2
5.0 10 -3
0.0 10 0
where N
2
AμB 1 emu K
≈
. Since the spin state is not necessarily known, the
3kB
8 Gauss mol
effective moment p is often reported where p 2 = g 2 J(J + 1). The Curie
susceptibility diverges as the temperature approaches zero; however, in real
systems the spins will Òfreeze-outÓ below some temperature making, for
example, an antiferromagnet, ferromagnet, or spin glass.
Magnetization (μ B /Fe)
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-80 -60 -40 -20 0 20 40 60 80
Magnetic Field (kOe)
0 50 100 150 200 250 300 350 400
Temperature (K)
Figure 3-4 Paramagnetic susceptibility and hysteresis loop of a
paramagnetic Fe containing organometallic compound [78].
Insulators with magnetic atoms far apart (do not interact) are good
examples of Curie paramagnets. Figure 3-4 shows the magnetic properties of
an organometallic compound [SC(CH3 ) 2C(CH3 )NCH2CH2NH2 ] -
2 FeCl with well
isolated Fe +3 ions [78]. The magnetization is slightly nonlinear at 5 K, as
predicted by the Brillouin function. The linear susceptibility can be fit to
χ = χ 0 + C/T where χ 0 is the diamagnetic correction (section 3.2.2.1.1). If the