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

R D Ralandinliu Kahmei,Sarath Arackal,S A Shivashankar,Ranajit Sai,Navakanta Bhat

doi:10.1063/9.0000190

Abstract

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.

Highlights

Nickel zinc ferrite (NZF) is one of the most explored soft magnetic materials due to its high saturation magnetization (Ms), high resistivity, high ferromagnetic resonance frequency (f FMR), high permeability (μ) and low loss, all of which are vital for high frequency applications.1–3 Besides vacuum-based deposition techniques NZF films have been deposited by various solution-based techniques such as spin-spray plating, spray pyrolysis, spin coating, sol-gel, and hydrothermal, and used in applications ranging from radio-frequency inductors to electromagnetic noise suppressors.4–8 Recently, we have developed a CMOS-compatible, low temperature Microwave-Assisted Solvothermal Deposition (MAS-D) process for various spinel ferrites and demonstrated its capability to yield smooth, uniform films with desired crystallite size.9–11 For example, a soft magnetic NZF thin film was successfully synthesized using ethanol:1-decanol as solvent, and its structural and magnetic properties thoroughly characterized.10 At 2.45 GHz, the timescale over which the field oscillates is about the same as the relaxation time (τ) of permanent dipoles in most organic and inorganic molecules
Via the Microwave-Assisted Solvothermal Deposition (MAS-D) process, we explored the impact of solution tanδ on the structure of the spinel nanocrystallites, and on the magnetic properties of the various Nickel zinc ferrite (NZF) films deposited on Si (100) substrates by using precursor solutions with various volume ratios of EA, Benzyl alcohol (BA), and D as solvents
The X-ray diffractometry (XRD) patterns (Fig. 2(a-e)) show crystalline cubic spinel phases, with average crystallite size of ∼6 to 8 nm in all samples

Summary

Introduction

Nickel zinc ferrite (NZF) is one of the most explored soft magnetic materials due to its high saturation magnetization (Ms), high resistivity, high ferromagnetic resonance frequency (f FMR), high permeability (μ) and low loss, all of which are vital for high frequency applications.1–3 Besides vacuum-based deposition techniques NZF films have been deposited by various solution-based techniques such as spin-spray plating, spray pyrolysis, spin coating, sol-gel, and hydrothermal, and used in applications ranging from radio-frequency inductors to electromagnetic noise suppressors.4–8 Recently, we have developed a CMOS-compatible, low temperature Microwave-Assisted Solvothermal Deposition (MAS-D) process for various spinel ferrites and demonstrated its capability to yield smooth, uniform films with desired crystallite size.9–11 For example, a soft magnetic NZF thin film was successfully synthesized using ethanol:1-decanol as solvent, and its structural and magnetic properties thoroughly characterized.10 At 2.45 GHz, the timescale over which the field oscillates is about the same as the relaxation time (τ) of permanent dipoles in most organic and inorganic molecules. Via the MAS-D process, we explored the impact of solution tanδ on the structure of the spinel nanocrystallites, and on the magnetic properties of the various NZF films deposited on Si (100) substrates by using precursor solutions with various volume ratios of EA, BA, and D as solvents.

Results

Conclusion