Superparamagnetic ultrathin films

Abstract

The finite-temperature magnetism of ultrathin films such as sesquilayer Fe/W͑110͒ and submonolayer Fe/Cu͑111͒ is investigated. Based on renormalizations of Onsager's exact solution of the two-dimensional Ising model it is shown that superparamagnetism is a common phenomenon in imperfect ultrathin films. The ultimate reason for this behavior is the existence of two structural length scales: the lattice constant, usually considered in renormalization-group theory, and the characteristic size of the film inhomogeneities.

Interface magnetism in epitaxial Fe/InAs heterostructures

“…2 show that the superparamagnetic phase also develops in Fe-InAs, but in an even narrower thickness range of about 2.5-3 ML. The s-shaped loop from the 3-ML film is consistent with the Langevin function used to describe the magnetization of superparamagnetic clusters [12], [13]. By fitting the curve, the effective magnetic moment per cluster is obtained to be (1.6 0.2) 10 .…”

Temperature dependent coercivity and magnetization of light rare-earth Nd doped permalloy thin films

“…5), by using the Scherrer equation, the average grain size is obtained, which shows a decreasing trend from 17.2 nm (X Nd ¼ 0%) to 8.7 nm (X Nd ¼ 3:4%), and the grain size could become smaller at amorphous state. It is known that when the grain size of ferromagnetic nanocrystal decreases to a very small value, the superparamagnetic order might appear [14]. We speculate that when the film structure changes from polycrystalline state to amorphous state with increasing Nd dopants, the grain size becomes smaller, leading to an effect of the superparamagnetic properties, which may be one of the reasons responsible for the big difference of hysteresis loop and coercivity at low temperature when the Nd concentration increases from 3.4% to 5.1%.…”

Growth and magnetism ofConanometer-scale dots squarely arranged on aCu(001)−c(2×2)Komori1, Lee2, Nakatsuji3 et al. 2001Phys. Rev. B390100View full textAdd to dashboardCite

“…20 Long-range ferromagnetic order was found to be established among superparamagnetic nanodots below T c through interdot magnetic coupling. In our films, superparamagnetism of each bilayer Co dot is ensured by interaction among the Co atoms in the dot, whereas interdot coupling is realized by monolayer Co regions.…”