Transition metals magnetism

As in the case of transition metals magnetism, the question of localized magnetic moments has been debated for some time and is still open. 

The magnetic moment m of the atoms in a nanostructure nearly exclusively originates from the electrons in the partially filled inner shells of transition or rare-earth metals. There are both spin (S) and orbital (L) contributions, but since L is much smaller than S in most iron-series transition-metal magnets, the magnetic moment is often equated with the spin polarization. The situation is similar to that encountered in bulk magnets, although both S and L may be modified at surfaces and interfaces (Ch. 2). As in infinite solids, nuclear moments are much smaller than electron moments and can be ignored safely for most applications. 

For one-sublattice magnets, such as Fe and Co, the Akulov or Callen and Callen theory [81] relates the temperature dependence of the anisotropy to the spontaneous magnetization and yields hi and Af° power laws for uniaxial and cubic magnets, respectively. This theory has become popular far beyond its range of applicability [82] but is unable to describe structures such as rare-earth transition-metal magnets [16, 60], actinide magnets [83], and L10 type compounds [44, 84]. 

Fig. 25. Process outline for the production of rare earth-transition metal magnet alloys by induction...

As said, the majority of these cases involve transition metal magnetism outside the scope of this review. Numerous classes of materials showing such behavior have been given special names and most were at least sampled by p.SR, such as Haldane gap (e.g.. 

From a theoretical point of view, the 3d electrons and the 4f electrons independently show some important characteristics, such as the Kondo effect and heavy-fermion behavior. The properties of the electrons have been studied by many researchers. A theoretical analysis of the electrons, however, in a physical sense, is still insufficient for explaining the magnetic properties of lanthanide-transition-metal magnets. The difficulties mainly come from the complexity of the mixture of the 3d and 4f electrons and of the interactions among them in these materials. 

Many important conclusions of the calculations can be found in the original papers quoted. In the following sections, therefore, we will discuss a few interesting points concerning the effects of the third element on the magnetic properties of the lanthanide-transition-metal magnets. 

Since 1987 many exchange-coupled rare-earth-transition-metal magnets have been developed. Examples of exchange-coupled magnets are listed in table 2. 

Short survey of the applications of rare earth-transition metal magnets... 

We now turn to a discussion of the Neel temperature. Our estimated Stoner temperature for UCuj is 1000 K. Given the experimental value of 15K, this implies that Tn is totally controlled by spin fluctuation effects, as observed for a number of transition metal magnets. This prompted us to calculate using spin fluctuation theory (Lonzarich 1986, Moriya 1987). For antiferromagnets, this formalism has been derived by Nakayama and Moriya (1987). The only change we make is to replace the assumed form of the susceptibility of Nakayama and Moriya by the Lorentzian form observed in neutron scattering. 

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