Two Dimensional Magnetic Properties of PdFe Layers
- PDF / 328,133 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 91 Downloads / 198 Views
Two-dimensional (2D) magnetism has been a subject of investigation for many years. The famous Mermin-Wagner [2] theorem shows that long-range magnetic order cannot exist at finite temperature for a 2D isotropic system of Heisenberg spins with short ranged interactions. Unfortunately, real 2D magnetic systems are never perfect and always exhibit a certain degree of anisotropy. The addition of anisotropic terms to the basic Heisenberg Hamiltonian allows finite temperature ordering to occur. The influence of finite size effects, magnetocristalline anisotropy and long-range dipolar interactions on the onset of long-range magnetic order has been studied theoretically by many authors [3,4,5,6]. On the experimental side, 2D magnetism has been widely investigated recently in ultra-thin films of 3d transition metals ferromagnets [7] but there are few clear reports of 2D Heisenberg magnetism
[8]. Evidence for a 2D Heisenberg behavior has been reported recently by Webb et al [1] in Pd with dilute Fe impurities (PdFe) thin films. As pointed out by these authors, PdFe is a very interesting system to investigate 2D magnetism. Bulk PdFe is a prototype "giant moment" magnet extensively studied in the litterature [9]. In contrast with PdCo and PdNi [10], PdFe is a 3D Heisenberg magnet with anisotropy and dipolar energies typically 2 orders of magnitude smaller than the exchange energy. From an experimental point of view it has also two additional advantages compared to 3d ferromagnets like Co or Fe. The distance between neighboring magnetic atoms (a critical length scale for 2D magnetism) is typically one order of magnitude larger which permits the use of non-monolayer films. Secondly, the (bulk) Curie temperature is strongly dependent on the Fe concentration and can be adjusted to be in a suitable temperature range for experimental investigation. In this paper, we report on the magnetic behavior of thin PdFe films grown by molecular beam epitaxy and confirm that PdFe behaves like a 2D Heisenberg magnet down to a given temperature where a cross-over to another behavior is observed.
259 Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
EXPERIMENTAL DETAILS
The samples were grown by molecular beam epitaxy on chemically etched and in-situ annealed Si(001) and Si(111) single-crystal substrates. The PdFe dilute-alloy layers were grown at room temperature using separate effusion cells for Fe and Pd. As the magnetization of a single PdFe layer is expected to be weak, we have used a multilayer geometry : the samples were made of three to six layers of 17A thick PdFe layers spaced by thick enough (80A) Pd spacer layers to avoid magnetic coupling between the PdFe films and reduce the strain related magnetic anisotropy. Prior to the multilayer deposition, buffer layers of Pd 80A and Ag 500A/Pd8OA were used on Si(001) and Si(111) respectively. During deposition, the sample holder was rotated in order to avoid anisotropic distribution. The alloy concentration was determined by separate calibrations of the two cells and b
Data Loading...
