Competition of the Coulomb and hoppingbased exchange interactions in granular magnets
Abstract
We study exchange coupling due to the interelectron Coulomb interaction between two ferromagnetic grains embedded into an insulating matrix. This contribution to the exchange interaction complements the contribution due to virtual electron hopping between the grains. We show that the Coulomb and the hoppingbased exchange interactions are comparable. However, for most system parameters these contributions have opposite signs and compete with each other. In contrast to the hoppingbased exchange interaction the Coulombbased exchange is inversely proportional to the dielectric constant of the insulating matrix ɛ . The total intergrain exchange interaction has a complicated dependence on the dielectric permittivity of the insulating matrix. Increasing ɛ one can observe the ferromagnetantiferromagnet (FMAFM) and AFMFM transitions. For certain parameters no transition is possible, however even in this case the exchange interaction has large variations, changing its value three times by increasing the matrix dielectric constant.
 Publication:

Physical Review B
 Pub Date:
 January 2017
 DOI:
 10.1103/PhysRevB.95.045427
 arXiv:
 arXiv:1702.00104
 Bibcode:
 2017PhRvB..95d5427U
 Keywords:

 Condensed Matter  Mesoscale and Nanoscale Physics;
 Condensed Matter  Disordered Systems and Neural Networks
 EPrint:
 13 pages, 7 figures