Abstract
Crystallographic inversion induced shift of resonance frequency in zinc ferrite nanoparticle (ZF-NP) samples is studied here. ZF-NP samples were synthesized by a solution-based, low-temperature (<200 °C), microwave-assisted solvothermal (MAS) process. Owing to the far-from-equilibrium processing condition, the MAS process produces a very high degree of crystallographic inversion, δ=0.61, in the as-synthesized nanocrystallites. A rapid thermal annealing (RTA) technique was adopted to tune-down crystallographic inversion without altering the crystallite sizes in annealed samples. The crystal structures, particle shapes, and compositions of the nanocrystalline samples were characterized by XRD, SEM and Raman spectroscopy. The samples are phase-pure, with particle size in the range 8-16 nm and their compositions are stoichiometrically accurate. The resonance phenomena in 1 to 10 GHz frequency range was measured by analyzing the impedance mismatch of a microstrip line with the magnetic material loaded on to it. The RTA protocol enables tuning of the resonance phenomena in the ZF-NC samples above 6 GHz with tunable range of ∼500 MHz
Highlights
Superparamagnetic relaxation (SR) is an important feature of the nanocrystalline ferrite particles in view of their applications in microwave frequencies.1,2. Owing to their very small volume (Vp), magnetic nanocrystallites often possess magnetic anisotropy energy (KVp; K: anisotropy constant) comparable to the thermal energy. This condition results in magnetization reversal triggered by thermal fluctuation at a certain temperature, T
As the frequency dependence of magnetic susceptibility of a single-domain superparamagnetic particle depends on the ratio of the anisotropy energy and thermal energy, the imaginary part of susceptibility, χ′′( f ), peaks at a frequency, fSR = 1/τ = f0e−KVp/kBT, known as superparamagnetic/ferrimagnetic relaxation rate
We have demonstrated controlled decrease of inversion without altering the crystallite size by fine-tuning a rapid thermal annealing protocol
Summary
Superparamagnetic relaxation (SR) is an important feature of the nanocrystalline ferrite particles in view of their applications in microwave frequencies. Owing to their very small volume (Vp), magnetic nanocrystallites often possess magnetic anisotropy energy (KVp; K: anisotropy constant) comparable to the thermal energy (kBT). Superparamagnetic relaxation (SR) is an important feature of the nanocrystalline ferrite particles in view of their applications in microwave frequencies.1,2 Owing to their very small volume (Vp), magnetic nanocrystallites often possess magnetic anisotropy energy (KVp; K: anisotropy constant) comparable to the thermal energy (kBT). As the frequency dependence of magnetic susceptibility of a single-domain superparamagnetic particle depends on the ratio of the anisotropy energy and thermal energy, the imaginary part of susceptibility, χ′′( f ), peaks at a frequency, fSR = 1/τ = f0e−KVp/kBT , known as superparamagnetic/ferrimagnetic relaxation rate.. As the frequency dependence of magnetic susceptibility of a single-domain superparamagnetic particle depends on the ratio of the anisotropy energy and thermal energy, the imaginary part of susceptibility, χ′′( f ), peaks at a frequency, fSR = 1/τ = f0e−KVp/kBT , known as superparamagnetic/ferrimagnetic relaxation rate.3 It increases with decreasing particle volume, known as nano-size-effect. We have demonstrated controlled decrease of inversion without altering the crystallite size by fine-tuning a rapid thermal annealing protocol
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