Apparent magnetic energy-barrier distribution in horse-spleen ferritin : Evidence for multiple interacting magnetic entities per ferrihydrite nanoparticle

• Magnetic viscosity measurements were made on native horse-spleen ferritin in zero applied magnetic field at temperatures between 21 and 21 K. The data have been used to calculate the apparent magnetic-moment-weighted energy barrier distribution for the sample of ferritin. The distribution is composed of a log-normal distribution plus a second distribution that is well described by an exponential decay of barrier frequency with increasing barrier height. The two distributions contribute approximately equally to the overall distribution. The log-normal distribution has its peak at an energy barrier of approximately 3 x 10(-21) J, while the decay constant for the second distribution has a value of approximately 2 x 10(-21) J. The existence of the low-energy barrier distribution with exponentially decaying shape in conjunction with the observation of shifted field-cooled magnetic hysteresis loops is interpreted as strong evidence for the existence of multiple interacting magnetic entities within each ferritin particle.

Nyckelord

macroscopic quantum coherence

antiferromagnetic ferritin

particles

proteins

spin

relaxation

cores

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