Magnetic moment clusters

Figure Cl.1.5. Nickel cluster magnetic moment per atom (p) as a function of cluster size, at temperatures between 73 and 198 K. Apsel S E, Emmert J W, Deng J and Bloomfield L A 1996 Phys. Rev. Lett. 76 1441, figure 1.

Hihara T, Pokrant S and Becker J A 1998 Magnetic moments and chemical bonding in isolated Bi Co clusters Chem. Phys. Lett. 294 357... 

Billas I M L, Becker J A, Chatelain A and de Heer W A 1993 Magnetic moments of iron clusters with 25 to 700 atoms and their dependence on temperature Phys. Rev. Lett. 71 4067... 

In this section, we compare our results for the magnetic moments of Ni, Fe and Co, n< 55, clusters with available experimental data. We point out that the determination of the exact ground state of these clusters is a very difficult task because these clusters exhibit a number of various spin states with energies lying very close to the ground state and within the range of both the calculational and the experimental errors. 

This example shows that dipolar interactions can produce unexpected effects in systems containing polynuclear clusters, so that their complete quantitative description requires a model in which the dipolar interactions between all the paramagnetic sites of the system are explicitly taken into account. Local spin models of this kind can provide a description of the relative arrangement of the interacting centers at atomic resolution and have been worked out for systems containing [2Fe-2S] and [4Fe-4S] clusters (112, 192). In the latter case, an additional complication arises due to the delocalized character of the [Fe(III), Fe(II)] mixed-valence pair, so that the magnetic moments carried by the two sites A and B of Fig. 8B must be written... 

Figure 5b. Variation in the magnetic properties of metal clusters are investigated by measuring the depletion of a highly collimated cluster beam by an inhomogeneous magnetic field. Fe clusters and their oxides (FexO and Fex02) at several applied fields. The uniform depletion of Fe clusters indicates that their magnetic moments increase approximately linearly with number of atoms, as would be anticipated for incipient ferromagnetic iron. Unexpected, however, is the much larger depletion of iron oxide clusters.

Figure 2. Plot of relative magnetization, a/Os ns a function of H/T. (a) A paramagnetic system Is characterized by an effective magnetic moment, with a Bohr Magneton number vlO per Ion, and by the absence of hysteresis. Paramagnetic saturation occurs at very high "H/T" == 10 Oe K"l. (b) l.angevln curve for S.P. clusters, (c) Part of a ferromagnetic hysteresis curve.

Here, yc stands for the (giant) magnetic moment of the cluster which replaces the "y" for single. Isolated paramagnetic spins k is the Boltzmann constant. 

Figure 9.9 Magnetic defects in FeO (a) antiferromagnetic alignment of magnetic moments in nominally stoichiometric FeO with the spins perpendicular to [111] (Z>) the simplest defect cluster in FeO, with the spin on the interstitial Fe lying in (111) and (c) antiferromagnetic coupling of the surrounding Fe ions with all spins lying in (111).

---