ИСТИНА

Magnetic oxides with a spinel structure are widely applicable in electronic devices. High resistance, the possibility of tuning of magnetic and electric properties, sipmle and cheap production makes them very useful for magnetic record, ferro-liquids, biosensors and other applications.[1] The valence and location of magnetic ions in octahedral [B] and tetrahedral [A] crystal sites can be varied by introducing different metal ions, size reduction, changing the condition of synthesis. Thus the information of such compounds tends to be vital and highly appreciated for theoretical and practical studies. A series of nickel-chromium-ferrite NiFe0.75Cr1.25O4 nanoparticles (NPs) with a cubic spinel structure and with size d ranging from 1.6 to 47.7 was synthesized by the solution combustion method. In the NPs with d > 20 nm, the compensation of the magnetic moments of A- and Bsublattices was revealed at about Tcom = 360-365 K. This value significantly exceeds the point Tcom in bulk ferrites NiFexCr2-x O4 (about 315 K) with the similar Cr concentration.[2] However, in the smaller NPs NiFe0.75Cr1.25O4 with d ≤ 11.7 nm the compensation effect does not occur. The magnetic anomalies are explained it the term of highly frustrated magnetic ordering in the octahedral B-sites, which appears due to the competition of AFM and FM exchange interactions, and results in a canted magnetic structure in the B sublattice.