Magnetic Properties at Nanoscale
Magnetic nano-particles have gain importance due to their specific properties associated with their finite size effects, size distributions, and inter-particle interactions. These resources can be applied for magnetic storage devices, ferrofluids, magnetic refrigeration systems, contrast enhancement in magnetic resonance imaging, magnetic carriers for drugs targeting or catalysis. Research in nano-structured magnetic materials has established the enormous perspective of their use in magnetic recording technology, for instance in the design of better recording heads and in development of high-density magnetic media. The magnetic recording technology uses the direction of the magnetic moments of the individual nano-particles arranged in a disk surface.
Furthermore, understanding of the magnetic properties at the nano scale has been a challenge for decades and prompted intense research activities in particular, by applications in magnetic resonance imaging, drug delivery, and hyper-thermic cancer treatments. A special behavior of magnetic nano-particles above a certain temperature is the occurrence of superparamagnetism, which arises from the thermal energy overcoming the magnetic anisotropy energy barriers of single-domain particles. Ultra-fine superparamagnetic particles can be prepared by several methods, such as chemical reduction, colloidal routes, vapor deposition, sputtering, melt-spinning, electrode-position, mechanical alloying. And for the confirmation of superparamagnetic state, magnetization can be measured with different temperature varies from 5k to 300k with presence and absence of magnetic field. A superparamagnetic state characterized by blocking temperature TB is defined as the temperature at which the hysteresis loop response is lost for a particular time frame of experiment [Fig.1]. Moreover, below TB, superparamagnetic materials lose its preferred direction of magnetization, and above TB, superparamagnetic materials can fluctuate randomly by thermal fluctuation. The variation in magnetic properties below blocking temperature is attributed to the existence of magnetic anisotropy barriers.
Recently using superparamagnetic materials enhanced magnetic resonance imaging technology has been developed to capture high-resolution images of cells and tissues. Superparamagnetic materials have also got applications in magnetic separation, where superparamagnetic particles are magnetized in the presence of applied magnetic field and during this process particles get agglomerated and after removal of the magnetic field get separated. Most recently superparamagnetic materials have found application in immunoassay due to its rapidly switching capability (magnetization and demagnetization) with respect to the external magnetic field. Therefore, it is intuitive that superparamagnetic materials have got incredible applications in the field of nano-science and bio-science. And in the future department of physics, faculty of science will try to synthesize and characterize superparamagnetic materials for application in biomedical sciences.
Dr. Mukesh Kumar
Department of Physics, Faculty of science
SGT University, Gurugram, Delhi-NCR