Magnetic behavior types

Magnesium(III) complexes structure, 66 Magnetic behavior types, 256... 

With a few exceptions, the crystal structure of the salts based on the type I mixed chains consists of parallel arrangements of those chains. In most cases the magnetic behavior of these salts is dominated by ferromagnetic (FM) interactions, due to intrachain D+ A coupling. Several of these salts exhibit metamagnetic (MM) behaviors due to the coexistence of weaker antiferromagnetic (AF) intrachain interactions. 

The magnetic behavior of [Fe(C5Me4SCMe3)2][M(mnt)2] (M = Ni, Pt) is dominated by FM interactions (6 — 3 K, M = Ni and Pt), which can be attributed to the D+A intrachain interactions. The weaker interchain interactions are expected to be AF. As in the previous compounds exhibiting this type of structure a metamagnetic behavior is also expected to occur at low temperatures. 

Most of the salts based on decamethylmetallocenium radical cations and on planar metal bisdichalcogenate radical anions reported so far present crystal structures with mixed linear chain basic motives. The only known exception is [Fe(Cp )2][Ni (mnt)2], which exhibits another type of crystal structure based on a D+ [A2]2 D+ repeat unit [28]. In the case of this compound the magnetic behavior is dominated by the intradimer antiferromagnetic interactions. 

Type of Magnetic Behavior Characteristics of Magnetic Susceptibility Typical Materials... 

Most of the important magnetic ceramics are of the ferrimagnetic class. However, some ceramics do exhibit other types of magnetic behavior. These ceramic materials will be described first, followed by a more thorough description of an important class of ferrimagnetic ceramics called ferrites. Finally, a topic related to the magnetic properties of ceramic superconductors will be introduced. 

Figure 1.41) have the oxygen ions in a nearly close-packed cubic array. The unit cell contains 32 oxygen ions, with 32 octahedral and 64 tetrahedral sites, of which 16 of the octahedral and 8 of the tetrahedral sites are filled. It is the position of these 24 cations within the unit cell that determines magnetic behavior. The distribution of cations in the sites is specific to the type of cations, and it must be determined experimentally. There are two idealized spinel structures. In the normal spinel, all the divalent ions are on the tetrahedral sites, as in ZnFe204. In the inverse spinel, the 8 occupied tetrahedral sites are filled with trivalent ions and the 16 occupied octahedral sites are equally divided between di- and trivalent ions (see Figure 6.63). The prototypical inverse spinel ferrite is magnetite, whose structure consists of an FCC oxygen array with Fe + and Fe + ions in the interstices.

In molecules, the interaction of surrogate spins localized at the atomic centers is calculated describing a picture of spin-spin interaction of atoms. This picture became prominent for the description of the magnetic behavior of transition-metal clusters, where the coupling type (parallel or antiparallel) of surrogate spins localized at the metal centers is of interest. Once such a description is available it is possible to analyze any wave function with respect to the coupling type between the metal centers. Then, local spin operators can be employed in the Heisenberg Spin Hamiltonian. An overview over wave-function analyses for open-shell molecules with respect to local spins can be found in Ref. (118). 

Figure 1.12. Schematic illustrations of the atomic origins of four types of magnetic behavior without external magnetic field (from Guy, 1976) (a) Diamagnetism (copper) ...

An iron complex can be formed by using the ethyl derivative of triphos, p3Etg [(triphos)Co(n3-P3)Fe(p3Etg)]2+. Many of the complexes here presented are paramagnetic. The number of valence electrons range from 30 to 34. This unprecedented magnetic behavior can be accounted for by a molecular orbital treatment of the type suggested by Hoffmann. 

In tetrameric structures, although the difference between intra- and intercluster distances is lower in fluorides than in oxides (3.73 and 4.90 A, 3.4 and 5.5 A in RuF5 and Na3Ru04, respectively), only the former compounds display a cluster-type magnetic behavior over a large temperature range. 

TABLE 8.1. Susceptibility for Different Types of Magnetic Behavior... 

Figure 8.2. Different types of magnetic behavior (a) a typicai M-H curve (both axes in Tesias) of a paramagnetic substance (b) a diamagnetic substance and (c) a ferromagnetic substance (note the change in the scaie of the M axis). An isotropic singie crystai, or poiycrystai with random crystaiiite orientation, is assumed.

---