Magnetic structure of Co$_{0.8-x}$Mn$_x$Zn$_{0.2}$Fe$_2$O$_4$ nanoparticles ($x$ = 0.6, 0.4 and 0.2) promising for biomedical applications

Magnetic nanoparticles (MNP) of ferrite Co$_{0.8-x}$Mn$_x$Zn$_{0.2}$Fe$_2$O$_4$ ($x$ = 0.6, 0.4 and 0.2) were synthesized by co-deposition. The structural, microstructural, magnetic and ultrathin properties of the obtained particles were investigated by X-ray diffraction and Mossbauer spectroscopy. The nanoparticle sizes calculated from radiographs at $x$ = 0.6, 0.4 and 0.2 are 15.2, 10.2 and 10.3 nm, respectively. The influence of the amount of Mn ions introduced on the properties of synthesized particles has been studied. The analysis of experimental Mossbauer spectra showed that the small size of the MNP leads to a significant increase in the effects of dimensionality and the influence of the surface on the magnetic structure of the surface layer. The Mossbauer studies, for the first time without the use of external magnetic fields, on the example of MNP spinel ferrites Co$_{0.8-x}$Mn$_x$Zn$_{0.2}$Fe$_2$O$_4$, found that inside the particle the magnetic moments are ordered collinearly, whereas in the surface layer the moments are oriented at an angle to each other (canting structure).