The impact of solvent tanδ on the magnetic characteristics of nanostructured NiZn-ferrite film deposited by microwave-assisted solvothermal technique

Nanostructured Ni-Zn ferrite (NZF) thin films, deposited by a CMOS-compatible microwave-assisted solvothermal deposition (MAS-D) process, exhibit ‘far-from-equilibrium’ distribution of cations in the spinel structure, and thus, exciting magnetic properties. Solvents with different dielectric loss-tangents, such as ethanol (tanδ≈0.94), 1-decanol (tanδ≈0.1), and benzyl alcohol (tanδ≈0.67), were mixed in five judiciously-chosen proportions – ED35 (ethanol:1-decanol=3:5; tanδ≈0.51), ED33 (tanδ≈0.63), EB25 (tanδ≈0.66), EB35 (tanδ≈0.70), and EB33 (tanδ≈0.74) – to study the impact of effective tanδ on cation occupancy and the nature of magnetization in the resulting films. The maximum temperature attained during microwave irradiation (Tmax) and the heating rate (∆T/trise) increase as the effective tanδ of the solvent mixture increases, which in effect leads the Ni atoms to migrate towards equilibrium lattice sites. Unlike bulk NZF, where all Ni atoms occupy octahedral sites (B-sites), the films reported here exhibit just 28% of Ni atoms in B-sites at best when deposited from the precursor solution EB25. At room temperature all films are superparamagnetic, while the maximum moment (MS=100 emu/cc) is observed in the film with the highest % of Ni atoms in B-sites. Thermoremanent magnetization (TRM) of the samples is studied and compared. Very high effective anisotropy constants (Keff=140 kJ/m3), and two-orders-of magnitude-higher inter-particle dipole moment (Edipole≈8×10-20 J @300 K) are observed in samples prepared from benzyl alcohol rather than 1-decanol – signifying the potential for tailoring magnetic properties by the choice of solvents in the MAS-D process.