Effective Specific Absorption Rate Research Articles

Insights on the Heating Characteristics of Mn and Co Ferrites

The heating characteristics of ferrite nanoparticles are inconsistent due to various factors that affect the optimum particle size required for maximum power dissipation. The heating mechanism of Fe3O4, MnFe2O4, and Co0.5Fe2.5O4 in the size range 10–40 nm with varying particle size distribution is correlated with the effective specific absorption rate (ESAR). The effective magnetic anisotropy of the ferrite samples determined using electron spin resonance is between 11.8 and 24.8 kJ· m−3. The thermal profiles of Fe3O4, MnFe2O4, and Co0.5Fe2.5O4 are probed employing infrared thermography where the measured ESAR is between 1.74 and 3.16 nHm2·kg−1. The theoretical ESAR of 16.63 and 9.19 nHm2·kg−1 are obtained for the Co substituted Fe3O4 and MnFe2O4, respectively, for an average size of 40 nm. The analysis of particle size distributions in combination with theoretical estimations gives the percentage of particles contributing to the power dissipation as 80 % for narrow dispersion and 45 % for broad dispersion deviating from the predicted optimum size range. In addition to ascertaining the functioning regime of the linear response theory, an increase in ESAR with decreasing anisotropy energy is observed. The discrepancy between the simulations and experimentations is prudently examined, taking the intrinsic as well as extrinsic parameters into account.

Role of magnetic anisotropy on the heating mechanism of Co-doped Fe3O4 nanoparticles

The heating characteristics of CoxFe3-xO4 (x = 0, 0.1, and 0.3) nanoparticles of average particle size 10–12 nm were investigated. The electron spin resonance analysis revealed an enhancement in magnetic anisotropy from 16 to 21 kJm−3 with low Co doping of x = 0.1. Magnetic measurements performed at 15 K showed a coercivity of 290 kAm−1 for the x = 0.1 composition, that decreased to 37 kAm−1 on surface modification. The effective specific absorption rate (ESAR) obtained using infrared thermography demonstrated a decreasing trend from 3.16 to 2.84 nHm2kg−1 due to the increase in magnetic anisotropy associated with Co substitution. An increase in ESAR up to 4.42 nHm2kg−1 was estimated with surface modification of Co-doped Fe3O4. The theoretically estimated ESAR considering polydispersity and experimental results presented decreasing behavior with magnetic anisotropy as per the linear response theory.

Factors affecting the heating efficiency of Mn-doped Fe3O4 nanoparticles

MnxFe3-xO4 (x = 0, 0.1, 0.3 and 0.5) nanoparticles were synthesized using the co-precipitation method and its structural and magnetic properties were correlated to the heating characteristics in an ac magnetic field. The effective magnetic anisotropy of the samples measured using electron spin resonance was between 15.3 and 16.5 kJ/m3 with Mn-doping. The effective magnetic anisotropy increased to 31.3 kJ/m3 on doping Fe3O4 with Co. The hyperthermia response of the samples was tested using infrared thermography and the effective specific absorption rate (ESAR) was obtained in the range of 15–21 × 10−9 W/gOe2Hz. The ESAR decreased when the effective magnetic anisotropy was 16.5 kJ/m3, as well as when it increased to 31.3 kJ/m3. The effect of magnetic anisotropy and polydispersity on the hyperthermic efficiency was intensively analyzed employing theoretical models.

Heating characteristics of dextran modified magnetite nanoparticles by infrared thermography

Magnetite nanoparticles were synthesized using co-precipitation and oxidation methods with average particle sizes of 12 and 60 nm respectively. Dextran coated magnetite nanoparticles were synthesized using oxidation method with an average particle size of 11 nm. The heating characteristics of the magnetic nanoparticles were studied using infrared thermography and the effective specific absorption rate (ESAR) was compared with the literature. The ESAR obtained in our present studies for the nanoparticles of similar size dispersed in water are 20 × 10−9 and 36 × 10−9 Wg−1Oe−2 Hz−1 for the uncoated and dextran coated magnetite respectively. The higher ESAR value for the dextran coated magnetite nanoparticles indicates that reduction in interparticle interaction influences the heating rate. The studies suggest that ESAR value could be used to determine the power dissipation contribution which follows the linear response theory.