Heavy lanthanide metals

From a magnetic point of view, Gd is the simplest of the lanthanide metals. Exchange favors FM, while all other heavy lanthanide metals initially show AFM order. The Curie temperature (7c = 293 K) is in a convenient temperature range. The Gd + ion has a half-filled 4f shell. It is thus an S state ion featuring pure (but very strong) spin magnetism. 

Discovery of the unique beautifiilly complex magnetic structures of the heavy lanthanide metals Discovery of the existence of the Sm(6)-phase in intra rare earth binary alloys... 

The second great theoretical thrust period took place in the mid- to late-1960 s when scientists were able to explain semi-quantitatively how the various striking and diverse magnetic structures occurred in the heavy lanthanide metals (Sinha 1978). Starting with the RKKY interaction and introducing the anisotropy of the 4f wave functions due to crystal field (see section 3.1) and other contributions, theorists were able to describe the occurrence of the various magnetic structures as a function of Z (the atomic number of the lanthanide) and temperature. 

Magnetic phase diagram for the heavy lanthanide metals... 

To reduce the cost of the reductant for Sm, Eu and Yb, mischmetal which has been vacuum melted to ISOtf C to remove the volatile impurities works well as a reductant in place of La. In the case of Tm the higher reduction-distillation temperatures as well as the higher sublimation temperatures sometimes cause a few ppm of Nd or the volatile heavy lanthanide metals in the mischmetal to be introduced in the sublimed Tm. La or Ce is used for the reduction of Tm when high purity is required. 

All of the rare earth metals can be machined with the possible exception of Eu. However, specimens of Eu with various shapes can be produced by extrusion. The standard procedures for machining soft steels should be followed. The turnings of the light lanthanide metals and impure Sc, Y and heavy lanthanides metals ignite easily and burn white hot, therefore, they should not be allowed to accumulate on the lathe, drill, or other machining device. 

Heavy lanthanide metals from Gd to Tm are all trivalent and have the common hep crystal structure. It is reasonable to expect that the sum in eq. (3.59) is nearly the same for all metals of this group. Then we find... 

Fig. 3.64. The magnetic structures of hep heavy lanthanide metals as revealed by neutron diffraction (Koehler, 1972).

The properties of the spin waves (magnons) in heavy lanthanide metals have been reviewed recently by Mackintosh and M0ller (1972). In the ferromagnetic state the spin wave spectrum of an isotropic spin system with long range interaction has the form... 

Magnetic ordering in alloys of heavy lanthanide metals 508... 

Fig. 7.1. Magnetic structures of heavy lanthanide metals [after Koehler (1972)].

The experimental evidence for these effects from neutron diffraction studies of individual heavy lanthanide metals is discussed in section 3. 

Fig. 7.4. Interlayer turn angle data vs. the de Gennes factor for the heavy lanthanide metals and binary alloys as determined from single crystal neutron diffraction experiments. o>i is the initial turn angle (just below Tn) [after Koehler (1972)]. Legend pure rare earth elements A Er-Dy alloys Er-Tb alloys V Er-Gd alloys O Ho-Dy alloys A Ho-Tb alloys.

The neutron diffraction results on the heavy lanthanide metals have been recently reviewed by Koehler (1972). The main features are summarized in tabic 7.1. We shall briefly review the results here. 

Rg. 7.37. The exchange function l (q) - 0)]l gj-lf along the c-axis for a number of heavy lanthanide metals in the cone (Er) and helical phases (after Hou-mann and Bjerrum-Mdiler, 1976). 

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