How small must particle be to be in single-domain state? 6.12J/3.155J Microelectronic processing Exchange length, 1, over which the magnetization is approximately parallel 2)l/2 λ=(AM2) 20 nm for Ni) A= exchange constant(10-6 erg/cm); M=saturation magnetization Domain wall width, SE IA/K, )/2 Sd particles K= anisotrop thermally decouple Superparamagnetism eQg I Single domain nm scale No on-unitorm d<入 25k T Multi-domain K micron scale d>>λ,6 (Semiconductor memory problem: CV2< kT) Dec.10,2003D e c. 10 , 2 0 0 3 6.12J / 3.155J Microelectronic processing How small must particle be to be in single-domain state? Exchange length, l, over which the magnetization is approximately parallel l = (A/Ms2)1/2 (20 nm for Ni) A = exchange constant (~10-6 erg/cm); Ms = saturation magnetization Single domain nm scale Non-uniform d < l d > l Domain wall width,d ≈ p(A/Ku)1/2, Ku = anisotropy. Multi-domain micron scale d >> l, d Vparticle £ 25kBT Ku SD particles thermally decouple: Superparamagnetism (Semiconductor memory problem: CV 2 < kBT )