Cool magnets
ever since the first patent for mechanical refrigeration was granted to Jacob Perkins in 1834, the quest for more efficient and faster refrigeration has been on. Lately, the emphasis has also been on making refrigeration less damaging to the environment as the chloroflourocarbon (cfc) gases are harmful to the ozone layer. The recent development of a new class of efficient magnetic material by V Pecharsky and K Gschneider of the Iowa State University, usa , might prove to be a turning point in the field (Science, Vol 279, No 5359).
Since the first refrigerator, the basic principle of cooling has remained unchanged. A fluid (refrigerant) changes from a liquid to a gas, thereby absorbing heat. Then the liquid is made to pass through a condenser by a compressor and the gas changes back to a liquid. This cycle is repeated, leading to the process of cooling.The technological improvement has been in the nature of the coolant used and in the efficiency of the compressors.
Magnetic refrigerators are of a different kind altogether. They work when a strong magnetic field forces the spins of electrons in atoms to align in a particular direction leading to an increase in the random velocities of the atoms. This energy is carried away by a coolant and the magnetic field is removed. When this happens, the spins lose their alignment leading to a cooling up of the atoms. This effect works only in a few materials, the best to date being gadolinium.
Pecharsky and his team have developed a new material by adding different quantities of silicon and germanium to gadolinium. This new class of materials can chill about two to six times further in a magnetic cycle. This means the refrigerator will use smaller magnetic fields and lesser material. Another advantage is that the new material can operate from room temperature to about -253