VÍTKOVSKÁ Nikola VSB - Technical University of Ostrava

Spoluautoři JANDAČKA Petr, ŽIVOTSKÝ Ondřej, LUŇÁČEK Jiří

The contribution presents interparticle magnetic interactions in dry ferrimagnetic single domain magnetite powder (the size of crystals being less than 50 nm) and in magnetite/magnesium oxide mixture powder (75 %, 50 % and 25 % of magnetite), where diamagnetic MgO powder is composed of micrometric grains. The study of magnetisation of magnetite nanoparticles in diamagnetic matrices was motivated by similar structures discovered in biological systems. Intensity of interparticle interactions was measured using vibrating sample magnetometer Microsense EV9 and characterised by magnetisation parameter M = Mvir – 0.5(Mup + Mdown) in Henkel plots, where Mvir is value of virgin curve, and Mup and Mdown are values of magnetisation in positive external fields of magnetisation curve. Clear magnetite powder exhibits typical negative (dipolar) interactions with the minimum of about 0.02 T at 20 °C, while at lower temperatures the interactions are stronger. Consequently, at temperature of -140 ºC the peak value moves up to 0.03 T. Partial substitution of magnetite by MgO significantly influences interparticle interactions. The intensity M increases in comparison to 100 % magnetite powder, while the position of peaks does not change much and slowly fluctuates between about 0.01-0.02 T. Moreover, sample with 25 % of magnetite exhibits also positive exchange interactions with magnetic fields of above 0.1 T (maxima). Taking into account the three contributions of magnetic energy, magnetic anisotropy energy, Zeeman energy, and interparticle magnetic energy, such results can be explained in the context of an interparticle shielding effect, when particles in the powder are more densely arranged.