Occurrence of
ferromagnetism at the room temperature (RTFM) in ZnO is connected to the presence of oxygen vacancies (VO) [4, 5], vacancies of Zn (V[Z.sub.n]) [6, 7], and interstitial atoms Zn ([Zn.sub.i]) [8].
Comparatively with undoped ZnO film, all Ni-doped ZnO films show distinctly hysteresis loops, indicating that samples have room-temperature
ferromagnetism. The magnetic moments increase with the content of Ni ions from [M.sub.s] = 5 x [10.sup.-7] A[m.sup.2] (for x = 0.03), [M.sub.s] = 2.4 x [10.sup.-6] A[m.sup.2] (for x = 0.05), and [M.sub.s] = 6 x [10.sup.-6] A[m.sup.2] (for x = 0.1).
In accordance with the TEM technique, all synthesized samples have unlike domains of nanoparticle sizes and those for x = 0.02 and 0.06 [less than or equal to] x [less than or equal to] 0.10, possess number of particles with sizes smaller than 35 nm that might explain the emergence of superparamagnetism and accordingly smaller contribution to
ferromagnetism.
The photoinduced
ferromagnetism is strongly affected by the photon energy itself rather than the intensity of the corresponding photon absorption.
We can see a similiar magnetic domain structure in the theoretical model of
ferromagnetism. In the case of Fig.2, the domain shape and the dipole direction tend to depend on the crystal structure.
Before tackling superparamagnetism, perhaps we should review the concepts of paramagnetism and
ferromagnetism as they apply to the magnetic storage of digital bits of information.
This alignment, called ferromagnetic coupling, rarely occurs naturally because electrons tend to spin in opposite directions, cancelling out any potential
ferromagnetism. But PMPOT-18's structure apparently encourages the necessary coupling.
There is even more variety in the electronic properties of various carbon allotropes, which range from superconductivity to
ferromagnetism and tunable electrical conductivity [1].
Manchanda et al., "Mn5Si3 Nanoparticles: Synthesis and Size-Induced
Ferromagnetism," Nano Letters, vol.
Wagner, "Absence of
ferromagnetism or antiferromagnetism in one- or two-dimensional isotropic Heisenberg models," Physical Review Letters, vol.
