Question

i) Give an example of confinement effects on magnetic materials?

ii) Given a Keff of 1E-5 J m3 please determine the critical size that you expect to have the confinement effect at 300K.

iii) And if it is at 100K?

iv) How you experimentally can detect this confinement effect?

v) What is the main advantage of this effect for particle applications?

vi) Give examples of applications.

Answer 1

Looking logically, there are electron waves everywhere. But, if we reduce the size of the particle, till its size becomes lesser than the electron waves, then it is roughly said confinement. Such small particles have remarkably different magnetic properties, just because due to small size, the fraction of molecules or atoms at the surface is very large, and such condition makes changes to properties.

superparamagnetism, ferrimagnetism etc in a material is an example of confinement effect.

I dont recall any direct relation between critical size and termperature. The critical size is the limit, beyond which if we confine the particle, its properties take a sharp turn or change. In most of the cases, as temperature rises the critical size increases. It depends on kind of chemistry which is being done there. There are paper reporting reverse case too. There are various parameters in this case, and a straight answer can not be given.

There is nothing like confinment effect. so far I understand, a series of effects are seen. Structure wise we do the x ray diffraction and find size and size distribution. The electron microscopes provide surface morphology. Vibrating sample magnetometers provide B H curve and this reveals many things. In addition to this, there are even more accurate measurement positron annihilation, mossbauer spectroscopy etc, which confirm that the confinement is done. It is a vast area of concern and perhaps most versatile in science now.  

The relationship of human beings with materials has consistently been getting stronger with the passage of time in the process of development. In the ancient times, our ancestors knew about stones, copper, bronze and iron and with the
passage of time, they came to know about ceramics and various alloys. In the past few decades, the material science has been dominated by artificially synthesized materials like nano materials, negative refractive index materials, conducting
polymers, organic magnetic materials, smart materials, immiscible alloys etc. The growth of technology is virtually dependent on the special properties which these materials have. We know that every material is made up of very minute atoms, but
during the formation of bulk materials these atoms form clusters or particles, whose size determines several important properties.

By doing confinement by various means, we can form particles having different properties from non confined state.