Magnetism of nanometer-scale iron particles arrays (invited)

The magnetization behavior in arrays of small ferromagnetic iron particles is investigated. Arrays were fabricated by a combination of chemical vapor deposition and scanning tunneling microscopy. This method allows a variety of particle arrays to be grown differing in particle height, diameter, or a rrangement. Moreover, the arrays can be grown directly onto different mater ials such as Au or permalloy. Magnetic measurements were conducted by Hall magnetometery up to 100 K and compared to switching field measurements by m eans of magnetic force microscopy at room temperature. The magnetization re versal mechanisms were studied from magnetization curves measured for an ar bitrary angle v of the applied field with respect to the long axis of the p articles. By analyzing the reversible rotation, the particles' magnetic cor e diameter and the shape anisotropy could be determined. A phenomenological model based on thermally activated magnetization reversal was introduced a nd compared to experimental switching field dependences on temperature as w ell as on v. Thermal effects may govern the magnetization reversal in parti cles of 10 nm diameter at all temperatures. For 14 nm particles and tempera tures below 30 K, curling (for v less than or equal to 30 degrees) and homo geneous reversal modes appear to dominate. (C) 1999 American Institute of P hysics. [S0021-8979(99)65308-7].