Dynamics and statistics study of rings formed by magnetic balls

The statistical distribution and stability of the ring structure formed by magnetic balls without a magnetic field are studied experimentally and theoretically. Experimental results show that the ring structure of the magnetic balls that are contacted one by one can easily appear. We tested 500 samples to count the probability, P(N), of the appearance of the rings and found that the number of balls, N, in a ring is limited only in the region from 4 to 20. The dependence of the probability, P(N), on the number of balls, N, follows a Poisson-like distribution. The origin of this Poisson distribution is disclosed by the statistics. Based on the classical “spin dynamics + molecular dynamics”, the stability of the ring structure was also investigated. The peak of function P(N) vs. N at 9 and the non-existence of rings with N=3 and N>20 is shown. An internal scaling relation between P(N) and the critical field h_c(N) for breaking the ring is found.