Experimental Studies on Verification of Single-Domain Particales of Ferromagnetic Materials and on Their Critical Sizes

Abstract

Small particles of ferromagnetic BaO⋅Fe₂O₃, SmCo₅, SM₂Co₁₇ and Nd₂Fe₁₄B compounds were prepared by the circumspect powder metallurgical method, and behaviours of their magnetic domains were studied with the decrease of the particle size.The colloid-SEM method invented by the present author was effectively used to observe domains of small particles less than 10 μm in size. With the decrease of the particle size the number of domains in one particle decreases, and finally the single-domain state is found for each compound, as expected by the theories. The critical size for single-domain particles, which is defined by the upper limit of the particle size range where the single-domain state can exist, is successfully estimated for all the above compounds from the particle size distribution curve of many single-domain particles, and obtained values of the critical sizes of the compounds are compared with the theoretical ones.