Crystallographic inversion-mediated superparamagnetic relaxation in Zn-ferrite nanocrystals

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

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

“…MAS-D process is well known for its kinetically driven crystal growth, which leads to far-from-equilibrium cation distribution inside the spinel structure of the nanocrystalline ferrite films. 16,17 The distribution of cations in the NZF lattice was examined by Raman spectroscopy. The spinel structure (space group Fd-3m) exhibits five Raman active modes: A 1g , Eg, and T 2g (1, 2 and 3) owing to the symmetric and asymmetric bending or stretching of oxygen ions bonded with the metal ions.…”

Unveiling the Hidden Entropy in ZnFe ₂O ₄

“…First, the sample was calcined for 2 h at 1100 • C with a slow cooling down at an average speed of 7 • C/min; the sample was named ZFO-0.05. Later, the commercial powder was milled up to 50 h in a Retsch PM4 planetary mill (Retsch GmbH, Haan, Germany), in a 250 cm 3 capacity jar and 1 cm diameter balls stainless steel, at a rotating speed of 275 rpm. This milled sample was then subjected to an annealing temperature of 400 • C for 1 h in order to decrease the inversion degree.…”

“…Zinc ferrites belong to the spinel structure (Zn 1-δ Fe δ ) A [Zn δ Fe 2-δ ] B O 4 , where A and B represent, respectively, the tetrahedral and the octahedral sites of the cubic structure and δ is the inversion degree parameter. There is a general agreement in the scientific community that δ plays the fundamental role in the magnetic properties of (Zn 1-δ Fe δ ) A [Zn δ Fe 2-δ ] B O 4 with δ = 0 [1][2][3][4]. For δ = 0, the ferrite is denominated normal, and it has been predicted to have an antiferromagnetic (AFM) transition around 10 K [5].…”

Unveiling the Hidden Entropy in ZnFe2O4

“…Zinc ferrites belong to the spinel structure (Zn 1-δ Fe δ ) A [Zn δ Fe 2-δ ] B O 4 , where A and B represent, respectively, the tetrahedral and the octahedral sites of the cubic structure and δ is the inversion degree parameter. There is a general agreement in the scientific community that δ plays the fundamental role in the magnetic properties of (Zn 1-δ Fe δ ) A [Zn δ Fe 2-δ ] B O 4 with δ ≠ 0 [ 1 , 2 , 3 , 4 ]. For δ = 0, the ferrite is denominated normal, and it has been predicted to have an antiferromagnetic (AFM) transition around 10 K [ 5 ].…”