Suppose you have a sphere of single-crystal cobalt with diameter L. For what values of L would you expect this to be a single domain particle? Assume the magnetostatic energy of a uniformly magnetized sphere of volume V = 4/3 pi (L/2)^3  is given by mu0 Ms^2 V

M_s = 1400 kA/m

K = 4 times 10^5 J/m^3

a = 0.25 nm

A = 10^{-18} J

Domain wall energy pi(2AK/a)^1/2

Q1.Particles remain single domain when L is less than what value?

Q2.We expect to observe superparamagnetism when L is less than what value?