Field dependent transition to the non-linear regime in magnetic hyperthermia experiments: Comparison between maghemite, copper, zinc, nickel and cobalt ferrite nanoparticles of similar sizes

Abstract

Further advances in magnetic hyperthermia might be limited by biological constraints, such as using sufficiently low frequencies and low field amplitudes to inhibit harmful eddy currents inside the patient's body. These incite the need to optimize the heating efficiency of the nanoparticles, referred to as the specific absorption rate (SAR). Among the several properties currently under research, one of particular importance is the transition from the linear to the non-linear regime that takes place as the field amplitude is increased, an aspect where the magnetic anisotropy is expected to play a fundamental role. In this paper we investigate the heating properties of cobalt ferrite and maghemite nanoparticles under the influence of a 500 kHz sinusoidal magnetic field with varying amplitude, up to 134 Oe. The particles were characterized by TEM, XRD, FMR and VSM, from which most relevant morphological, structural and magnetic properties were inferred. Both materials have similar size distributions and saturation magnetization, but strikingly different magnetic anisotropies. From magnetic hyperthermia experiments we found that, while at low fields maghemite is the best nanomaterial for hyperthermia applications, above a critical field, close to the transition from the linear to the non-linear regime, cobalt ferrite becomes more efficient. The results were also analyzed with respect to the energy conversion efficiency and compared with dynamic hysteresis simulations. Additional analysis with nickel, zinc and copper-ferrite nanoparticles of similar sizes confirmed the importance of the magnetic anisotropy and the damping factor. Further, the analysis of the characterization parameters suggested core-shell nanostructures, probably due to a surface passivation process during the nanoparticle synthesis. Finally, we discussed the effect of particle-particle interactions and its consequences, in particular regarding discrepancies between estimated parameters and expected theoretical predictions.

Controlled Electrodeposition and Magnetic Properties of Co35Fe65Nanowires with High Saturation Magnetization

“…56 For a specific magnetic material, there is a critical diameter (d cr ,) below which curling cannot occur because the nanowire is too small to support a vortex core. The core size can be calculated using equation 11,55 where A is the exchange stiffness and M s is saturation magnetization. d cr = 2.08 A 1/2 /M s [11] For small nanowire diameters (d < d cr ) the preferred mode is coherent rotation (CR), while for d > d cr the curling mode (C) is expected.…”

“…The core size can be calculated using equation 11,55 where A is the exchange stiffness and M s is saturation magnetization. d cr = 2.08 A 1/2 /M s [11] For small nanowire diameters (d < d cr ) the preferred mode is coherent rotation (CR), while for d > d cr the curling mode (C) is expected. 51,52 By assuming A = 10 −6 erg/cm and taking M s -values in emu/cm 3 from Table I, the critical diameters for Co 35 Fe 65 nanowires were calculated as 10.2 nm.…”

Manganese ferrite-based nanoparticles induce ex vivo, but not in vivo, cardiovascular effects

“…33 In the magnetic fluid preparation, precipitate was fractioned and nanoparticles peptized in aqueous solution, after their surface modification, using three distinct procedures, which are schematized in Figure 1: 1) for one of the samples, the precipitate was acidified with 50 mL of 1.0 mol/L HNO 3 solution; 2) another sample was treated with sodium citrate, under stirring for 30 minutes, using a mass ratio of 1:20, Na 3 C 6 H 5 O 7 to manganese ferrite, in 50 mL of water; and 3) in the sample, the precipitate was treated with sodium tripolyphosphate, under stirring for 60 minutes, using a mass ratio of 3:20, Na 5 P 3 O 10 to manganese ferrite, in 50 mL of water. 30 In all the cases, the obtained precipitates were magnetically separated and supernatants discarded. Afterwards, the precipitates were washed with acetone three times, then the desired amount of water was added and the excess of acetone evaporated in order to form the magnetic fluid samples.…”

“…16,28 Some nanoparticles were surface-coated with citrate (the coating agent already used for magnetic resonance image -see Sosnovik et al 29 ) or tripolyphosphate. 30 These nanoparticles (CiMNPs and PhMNPs) are stable at physiological conditions and have a negative surface charge. The third nanoparticle type (BaMNPs) is ionic and has a positive surface charge at acidic conditions; however, at physiological conditions, it is not stable and has no surface charge.…”

The pronounced role of impurity phases in the optical properties of Mn catalyzed ZnS nanostructures

“…4 Ferrite nanoparticles have been proposed to be helpful in several biomedical applications on targeting, diagnosis and disease treatment. 5 Several techniques have been employed in the growth of 1-D nanostructures such as electrochemical deposition, 6 solvothermal, 7 homoepitaxial growth, 8 chemical vapor transport, 9 vapor liquid solid, 10,11 etc., The synthesis of 1D nanostructures by vapor liquid solid (VLS) mechanism is one of the simplest way of growth and is widely used for obtaining single crystalline 1-D nanostructures. The VLS method requires a metal liquid droplet as a catalyst, which adsorbs the gaseous species of the source material followed by the nucleation and growth of the nanowires.…”