Friday, January 18, 2013

1301.4111 (Akash Chakraborty et al.)

Spin-wave excitations in presence of nanoclusters of magnetic impurities    [PDF]

Akash Chakraborty, Paul Wenk, Stefan Kettemann, Richard Bouzerar, Georges Bouzerar
Nanoscale inhomogeneities and impurity clustering are often found to drastically affect the magnetic and transport properties in disordered/diluted systems, giving rise to rich and complex phenomena. However, the physics of these systems still remains to be explored in more details as can be seen from the scarce literature available. We present a detailed theoretical analysis of the effects of nanoscale inhomogeneities on the magnetic excitation spectrum in diluted systems. The calculations are performed on relatively large systems (up to $N$=$66^3$). It is found that even low concentrations of inhomogeneities have drastic effects on both the magnon density of states and magnon excitations. These effects become even more pronounced in the case of short ranged magnetic interactions between the impurities. In contrast to the increase of critical temperatures $T_C$ reported in previous studies, the spin-stiffness $D$ is systematically suppressed in the presence of nanoscale inhomogeneities. Moreover $D$ is found to strongly depend on the inhomogeneities' concentration, their size, as well as the range of the magnetic interactions. We believe that this detailed numerical work could initiate future experimental studies to probe this rich physics with the most appropriate tool, Inelastic Neutron Scattering (INS).
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