Itinerant Magnetism Transition-metal Compounds

Experimentally, Mg2MnRhsB2 is characterized by Curie-Weiss behavior a-bove 160 K with a Weiss constant of —130 K. The latter information stands 

11) The small differences between experimental and theoretical moments do not necessarily go back to theory problems but might also be explained by the fact that the experimental measurements were carried out on a nonstoichiometric (Mn-rich) compound. 

12) Upon integration of the Mn-Sb and Mn-Mn bonds for the spin-polarized case, however, it is found that both kinds of bonds weaken upon spin-polarization although antibonding states are removed from the Fermi level. This is a clear sign that the antibonding character of the states around the Fermi 

Sc2FeRh5B2 (b). The shaded regions indicate charge enrich-ments/depietions by ca. three eiectrons with respect to the (zero) Fermi level. 

The search for new magnetic materials as described in the last section may be looked upon as a typical example of the chemist s orthodox strategy Namely, take your existing compound, analyze the interactions between the atoms, understand them using some theoretical framework - and then move on to rationally synthesize yet another compound with a new composition Making new compounds is at the heart of chemistry, and chemists really love to fabricate them. And yet, there are other ways of arriving at new materials. 

---

Transport properties of rare earth-transition metal compounds exhibiting itinerant magnetism... 

Few materials show up the limitations of the two extreme viewpoints of magnetic moment formation in transition metal systems ( localized or itinerant ) more than do their intermetallic compounds. In some compounds, e.g., the (non-integral) magnetic moment may vary from one type of site to another and the moment associated with a particular transition metal atom is often different in its different compounds. The interest in the wide variety of properties exhibited by intermetallic compounds stems as much from the opportunity they offer for the understanding of magnetism in metallic systems at a fundamental level as from the possibility of producing materials of technological importance. 

It would not be appropriate here to discuss the many points at issue in the intense international debate which has been going on for some time in this area. The comments of the discussion panel at the international conference on magnetism in Kyoto, ICM 82, provide a convenient summary (Kanamori 1983) and a book dedicated to itinerant magnetism is now available (CapeUmann 1987). We shall therefore give only a brief outline of the expectations of those theories which are currently used by the majority of experimentalists in attempting to explain the observed ferromagnetic behaviour of the transition metal intermetallic compounds. 

A more complex magnetic behaviour is expected for RI compounds in which the second component is a 3d transition metal such as Mn, Fe, or Co. The magnetic behaviour of the transition metal component is now based on the magnetic polarization of the electronic d-bands. Consequently, in this section we summarize the theory of itinerant or band magnetism and its application to transport properties. We begin with the Stoner-Wohlfarth model and include a summary of recent works. 

---