What is an exchange stiffness in ferromagnetic materials and what is the role of exchange stiffness ?
Dear Saravanan,
The exchange stiffness constant, usually denoted by A, serves as characteristic of a ferromagnetic material instead of the exchange integral J alone between two spins. Besides the J coupling it also introduce a dependence on the crystal structure giving a kind of density of exchange magnetic energy with respect to the lattice constant for certain discrete symmetries as simple cubic, face centered cubic or body centered cubic.
I hope that this could be helpful.
For further information:
U. Schollw ̈ock, J. Richter, D.J.J. Farnell, R.F. Bishop, Quantum Magnetism, Lecture Notes in Physics 645,Springer-Verlag, Berlin, (2004).
is the exchange stiffness constant always positive. For YIG, which is ferrimagnetic J is negative but reported values of A are positive
Dear Pramod,
The stiffness constant A has always the same sign as the J exchange constant by definition
A= (n S2/a) J
Notice that the quantity between parenthesis is always positive n takes into account the symmetry of the lattice ( n=1 simple cubic, n=2 bcc, n=4 fcc), S=spin and a= lattice constant
Dear Prof. Daniel Baldomir ,
What is the relation between the exchange stiffness A and the exchange energy Jij ?
Dear Akhil,
The magnetism depends strongly of the length scale that is described by the different models. The most fundamental is the atomistic where the coupling constant J between pair of spins gives their interaction, but there is also another at microns scale where the magnetic domains play a basic role where the spin stiffness A "substitutes" the J. The most simple relationship between A and J is the one that I have given some years ago
A= (n S2/a) J
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