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Vallejo-Fernandez G.,University of York | Ogrady K.,University of York | Ogrady K.,Liquids Research Ltd
Applied Physics Letters | Year: 2013

Magnetic hyperthermia using magnetic nanoparticles is a potential remedial therapy for the reduction of cancer and other tumours. The dominant heating mechanism is hysteresis heating. This means that control of the particle size distribution is essential. However, control of the anisotropy dispersion is also required. We have calculated the effect of the anisotropy distribution on the hysteresis heating in magnetic nanoparticles for hyperthermia applications. Where there is a wide distribution of anisotropy constants the heat output is controlled by the distribution of anisotropy constants. This effect is significant in systems such as magnetite particles where shape anisotropy dominates. © 2013 AIP Publishing LLC.

Roca A.G.,University of York | Wiese B.,University of York | Timmis J.,Liquids Research Ltd | Vallejo-Fernandez G.,University of York | O'Grady K.,University of York
IEEE Transactions on Magnetics | Year: 2012

We have undertaken studies of the heating rate in three sets of magnetic nanoparticles for their application in magnetic hyperthermia. The nanoparticles were magnetite-maghemite with average particle diameters of 5, 28, and 45 nm, respectively. All samples were synthesized in an aqueous media and have a narrow size distribution. These sizes represent particles which are single domain, particles which lie close to the single domain multi-domain boundary, and particles which are probably multidomain. The heating rate is greater for the largest particles when an alternating magnetic field of 250 Oe and a frequency of 110 kHz are applied. The significant increase in heating for the 45 nm particles suggests that heating may be associated with particle rotation. © 1965-2012 IEEE.

Vallejo-Fernandez G.,University of York | Whear O.,University of York | Roca A.G.,University of York | Hussain S.,Liquids Research Ltd | And 4 more authors.
Journal of Physics D: Applied Physics | Year: 2013

We report on a theoretical framework for magnetic hyperthermia where the amount of heat generated by nanoparticles can be understood when both the physical and hydrodynamic size distributions are known accurately. The model is validated by studying the magnetic, colloidal and heating properties of magnetite/maghemite nanoparticles of different sizes dispersed in solvents of varying viscosity. We show that heating arising due to susceptibility losses can be neglected with hysteresis loss being the dominant mechanism. We show that it is crucial to measure the specific absorption rate of samples only when embedded in a solid matrix to avoid heating by stirring. However the data shows that distributions of both size and anisotropy must be included in theoretical models. © 2013 IOP Publishing Ltd.

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