Long-range antiferromagnetic ordering

Temperature dependence of magnetic susceptibility of the PF6 salt was measured from 300 to 4 K at 5 T [35], The spin susceptibility of this salt gradually decreases from 300 to 50 K. Below 50 K, the susceptibility exhibits a rapid decrease accompanied by anisotropic temperature dependence, which is an indication of the long-range antiferromagnetic ordering. A one-dimensional Heisenberg model is... 

An important property of the Fermi surface is that the volume (in /c-space) that it encloses is not altered by the interaction between the electrons, unless long-range antiferromagnetic order is set up. This was first shown by Luttinger (1960). We shall make use of this theorem in Chapter 4, Section 3 in discussing metal-insulator transitions due to correlation. 

In accord with the Hohenberg-Mermin-Wagner theorem [15] the considered two-dimensional system is in the paramagnetic state for T > 0. This result can also be obtained using Eq. (8). Also it can be shown [7] that in the infinite crystal at T = 0 the long-range antiferromagnetic order is destroyed for the hole concentrations x > xc 0.02. 

Figure 7. Low-temperature phase diagram of the UlPf.xPdJ., system SC denotes superconductivity, SMAF small-moment antiferromagnetism and LMAF long-range antiferromagnetic order data from ref. [42],...

At further increase of x, the long-range antiferromagnetic order is lost and a Kondo-type of behaviour is found in the resistivity curves of compounds withx > 0.10. 

Figure 10. Antiferromagnetism in U(Pto 99Pd0 01)3 below 6 K as studied in neutron diffraction (upper figure) and pSR experiments (lower figure) the long-range antiferromagnetic order below 2 K is visible in both experiments the weak antiferromagnetism that does not show up in the pSR data gradually weakens with increasing temperature and disappears above 6 K data from ref. [20].

Whereas long-range antiferromagnetic order should occur for n2g = 3, a breakdown of simple antiferromagnetic order may occur if n2g < 3, that is, if the collective electrons responsible for coupling the localized spins occupy partially filled bonding bands. 

Neutron diffraction data show long-range antiferromagnetic ordering in UCI3 below 6.5 K (180) and in UI3 below 2.8 K (181). 

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