A method for measuring the Neel relaxation time in a frozen ferrofluid

We report a novel method of determining the average Neel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm +/- 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Neel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results

Determination of the Magnetocrystalline Anisotropy Constant from the Frequency Dependence of the Specific Absorption Rate in a Frozen Ferrofluid

Colloidal suspensions of superparamagnetic nanoparticles, known as ferrofluids, are promising candidates for the mediation of magnetic fluid hyperthermia (MFH). In such materials, the dissipation of heat occurs as a result of the relaxation of the particles in an applied ac magnetic field via the Brownian and Neel mechanisms. In order to isolate and study the role of the Neel mechanism in this process, the sample can be frozen, using liquid nitrogen, in order to suppress the Brownian relaxation. In this experiment, dextran-coated Fe3O4 nanoparticles synthesized via co-precipitation and characterized via transmission electron microscopy and dc magnetization are used as MFH mediators over the temperature range between −70°C to −10°C (Brownian-suppressed state). Heating the nanoparticles using ac magnetic field (amplitude ∼ 300 Oe), the frequency dependence of the specific absorption rate (SAR) is calculated between 150 kHz and 350 kHz and used to determine the magnetocrystalline anisotropy of the sample

A Method for Measuring the Néel Relaxation Time in a Frozen Ferrofluid

We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H0=20H0=20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results

Total Amount Requested $1997.00 Student Research Team:

We propose to synthesize and characterize magnetic microbubbles for examining the use of magnetic microbubbles for targeted drug delivery. Using magnetic microbubbles as carriers, we will test how well drugs can be dispersed by means of ultrasound and hyperthermia. Proposal Statement Overview of Proposed Project Ultrasound microbubbles (UMB) are tiny gas-filled lipid shells that have a variety of medical uses. One use is the delivery of anti-cancer drugs. UMB carrying an anti-cancer drug can be exposed to ultrasound to release their payload. Magnetic Microbubbles (MMB) are UMB with a shell of embedded magnetic nanoparticles (MNP). Magnetic nanoparticles that go into the UMB can also have anti-cancer drugs attached. Faculty at our university have been working with UMB, MMB and MNP in various research projects. Currently, there is research into the use of MMB for targeted drug delivery (1). This involves using the magnetic properties of MMB to guide them to and concentrate them in a specific region, which may result in better drug delivery over UMB. We wish to test if MMB have the same capacity for drug release as UMB. Determining that MMB and UMB have equivalent dispersal will show the feasibility of MMB for drug delivery. We also want to determine if magnetically-induced hyperthermia (the heating that occurs when MNP are exposed to alternating magnetic fields