Abstract
Magnetic vortices existing in soft magnetic nanoparticles with sizes larger than the single-domain diameter can be efficient nano-heaters in biomedical applications. Using micromagnetic numerical simulation we prove that in the optimal range of particle diameters the magnetization reversal of the vortices in spherical iron and magnetite nanoparticles is possible for moderate amplitudes of external alternating magnetic field, H0 < 100 Oe. In contrast to the case of superparamagnetic nanoparticles, for the vortex configuration the hysteresis loop area increases as a function of frequency. Therefore, high values of the specific absorption rate, on the order of 1000 W/g, can be obtained at frequencies f = 0.5–1.0 MHz. Because the diameter D of a non single-domain particle is several times larger than the diameter d of a superparamagnetic particle, the volume of heat generation for the vortex turns out to be (D/d)3 times larger. This shows the advantage of vortex configurations for heat generation in alternating magnetic field in biomedical applications.
Highlights
The local increase of tissue temperature might be achieved using ultrasound, microwaves, or near-infrared radiation[7]
To the human body if its amplitude and frequency f satisfy the condition fH0 < 5×109 A/(ms). It is the superparamagnetic nanoparticles with diameters substantially smaller than the single-domain diameter Dc that have been investigated in recent experimental and theoretical studies in magnetic hyperthermia[13,14,15,16,17,18,19,20,21,22,23,24,25,26]
Let us first consider iron nanoparticles, which are especially interesting for use in magnetic hyperthermia[14,15,16] due to the high saturation magnetization of iron, Ms = 1700 emu/cm[3]
Summary
The local increase of tissue temperature might be achieved using ultrasound, microwaves, or near-infrared radiation[7]. It is preferable to use magnetic nanoparticle with sufficiently large SAR value. It is important to ensure the magnetization reversal of magnetic nanoparticle assembly in an alternating magnetic field of moderate amplitude, H0 < 100–200 Oe. the use of strong alternating magnetic field requires generation of sufficiently large electric currents. The use of strong alternating magnetic field requires generation of sufficiently large electric currents It might be dangerous in a clinic. In the experiment sufficiently large cubic nanoparticles can be obtained by various methods[17,20,22,35,36,37] These particles have a perfect crystal structure[36] as their magnetic characteristics are close to the corresponding values for bulk material[38]
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