Magnetic Nanoparticles

Magnetic nanoparticles like iron oxide FeOx show different magnetic properties with variation of particle size. If and when the size of the particle falls below the dimension of a so called Weissche domain (the area within a magnetic material, in which the spins are oriented parallel) it does only consist of one shear-oriented block. This characteristic dimension is called single domain size DS and lies typically between 10 and 100 nm.

The behavior of particles with just one shear-oriented block differs from general behavior of ferromagnetic materials. Such is the coercivity HC bigger than in macroscopic analogues, because the direction of magnetization can only be influenced by coherent, thus simultaneously spin rotation of spins in the particle, and not through deferral of domain walls. However, this process needs more energy. If the particle size decreases, the area of the shear-oriented block diminishes and therefore the number of equal spins. As because of this the needed energy for coherent spin rotation decreases, the amount of HC gets smaller. Starting from a characteristic particle size the coercivity becomes zero, this is called superparamagnetism. In this case the spin rotation is energetically very less hindered so that rotation even at room temperature gets feasible. The anisotropic energy Ea behaves proportional to the particle volume.

We offer in our CANdots Series M magnetic nanoparticles with a size of 10 nm. With this size the crystals are one-domain particles with superparamagnetic behavior. This property combined with a good solubility in aqueous solution and long-term stability makes these particles ideal for the use as contrast agent on the base of T1 und T2 relaxation measurements.

Dr. Jan Niehaus

Dr. Jan Niehaus

Dr. Christoph Gimmler

Dr. Christoph Gimmler

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CANdot Series M