NATURE OF MAGNETISM IN Cr NANOPARTICLES PRODUCED BY BALL MILLING

摘要

Detailed measurements of magnetization M as a function of temperature T (5 ― 350 K) and magnetic field H (up to 55 kOe) are reported for the 290 A nanoparticles of Cr produced by ball milling. The M vs H data fits the modified Langevin function M = M_0L(μ_pH/kT) + x_aH from which μ_p = 10~4 μ_B/particle is determined. The M vs T data for the field-cooled (FC) and zero-field-cooled (ZFC) cases resembles that expected for a superparamagnet with a particle size distribution and average T_B ～ 100 K. Hysteresis loops at 10 K are identical for the ZFC and FC (H = 10 kOe) cases, confirming superparamagnetism.