Ferromagnetic states

Figure 8.9 Schematic illustrations of spin states in a two dimensional periodic material. Circles indicate individual atoms and the dotted lines show a single supercell. In (a), all electrons are paired on each atom. In the remaining examples, a single unpaired electron exists on each atom. Examples of a ferromagnetic state, an antiferromagnetic state and a more complex mag netic state are shown in (b), (c), and (d), respectively.

I shows a magnetic moment of 2.71 between 100 and 300 K. Since there is no specific short contact between the molecules, there is no ferromagnetic interaction in the solid state. Among the nonmetallic molecular magnets known, Cgo TDAE where TDAE = (Mc2N)2 C=C(NMe)2, which orders into an itinerant ferromagnetic state with a of... 

MnAs determined from (Ga,Mn)As and (In,Mn)As data show a good correspondence. This suggests that virtually all Mn atoms occupy the substitutional sites. The lattice constant of hypothetical zincblende MnAs in the ferromagnetic state has been predicted to be 0.S9 nm by first-principle calculations (Shirai et al. 1998 Ogawa et al. 1999). 

III- V barrier layers, where impurities are incorporated, provide carriers to II-VI magnetic layers. The results of the first principle calculation for a AlAs C/(Cd,Mn)Te superlattice shows that the ferromagnetic state is indeed stable for high concentrations of C. 

Results of a first principles calculation shows that the antiferromagnetic state is more stable than the ferromagnetic state, and that the energy gap decreases with the Mn composition (Zhao, Y.-J. et al. 2001b). The reason for the discrepancies between theoretical expectations and experimental results is not clear it may stem from the substitution of Ge for Mn in surface-doped samples. More recent plane-wave pseudopotential and KKR-CPA calculations show that the intrinsic defects are responsible for the stabilization of the ferromagnetic state (Mahadevan and Zunger 2002 Kamatani and Akai 2001b). 

Kadomtseva et al. (2000) measured thermal expansion and longitudinal and transverse magnetostriction in pulsed magnetic fields up to 25 T in Lai - Sr MnOj single crystals (x = 0.1,0.125 and 0.15). The results were ascribed to a suppression of the O phase and field-induced transitions to a new orbital-ordered ferromagnetic state. 

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