Question

Difference between ferromagnetism ferrimagnetism and antiferromagnetism

Answer 1

Ferromagnetic materials usually contain domains of various sizes. The spin magnetic moments in each domain are generally aligned parallel to each other. As a result each domain exhibits saturate magnetization in a particular direction that is parallel to the direction of spin moments. The vector sum of the magnetic moments from all thedomains results in a non-zero magnetization and is commonly referred asthe spontaneous magnetization. The following figure illustrates the generalalignment of spins in different domains of a typical ferromagnetic material. The figure isfor illustrative purpose only.The left figure represents the ferromagnetism. There are a total of 6 domains shown in thefigure. The black arrows represent the spin magnetic moment vectors and are aligned in a particular direction in each domain. The magnitude of vectors indicate the magnitude of spin moment. The vector sum of spin momentsfrom all the 6 domains results in a non-zero magnetization. If you carefully notice the figure you will find that all the black arrows are same in size i.e. from the arrow tip to tail. It is conventional that the spin moments are generally representedby arrows (vectors). Each arrow represents a spin moment with a finite magnitude. The samesize represents that the magnitudes of all spin moments are equal.Example: Fe, Co and Ni etc.Anti-Ferromagnetic Materials:These are similar to Ferromagnetic materials but the spinmoments in each domain are aligned opposite to each other as represented in the middle figure. Consequently, each domain results in a zero magnetization and hence a zero spontaneous magnetization.Examples: Chromium,FeMn alloy and NiO etc.Ferrimagnetic materials:These are similar to anti-ferromagnetic materials, but the magnitude of one set of spins (say parallel spins) is not equal to the magnitude of other set of spins (say opposite spins). The top right figure represents the same. As a result each domain results in a non-zero magnetization and hence a non-zero spontaneous magnetization of the whole sample. The difference in magnitudes comes from the atomic elements which occupy different sitesexhibit different magnitudes of spin moments.