On the theory of indirect exchange in EuO

Abstract

We present the calculations of the Curie temperature and magnetization of doped EuO both in the absence and in the presence of external magnetic field. The calculations were performed both for the free electrons model and for the model with finite electron band width. Both models give similar results for the magnetization, close to Brillouin function.Comment: PdfLatex, 7 pages, 12 Figures. Accepted for publication in Physica Status Solidi(b

Theory of Curie temperature enhancement in electron-doped EuO

“…For short Fermi wavelength, the RKKY interaction might make an AF contribution to the total coupling and, thus, lead to the experimentally observed saturation of T C [5,[18][19][20][21][22], as has been suggested in Ref. [26]. In order to analyze the possible influence of the RKKY interaction on the saturation at high doping concentration, we now adjust the value of J cf such that the theory including RKKY reproduces the previous results without RKKY interaction (Sec.…”

“…It has been proposed [26,27] that the T C saturation might be understood in that, for increasing conduction-band filling, the oscillatory RKKY interaction [28][29][30] acquires increasingly antiferromagnetic (AF) contributions due to the decreasing RKKY wavelength. This requires, however, unrealistically high band filling.…”

Influence of chemical doping on the magnetic properties of EuO

“…2), because the highest T C in the model is reached for n ≈ 10 21 cm −3 . 26,27 This emphasizes the necessity to base the comparison between experimental data and theory on measured carrier densities rather than on dopant concentrations. charge carrier density and dopant activation, its zero-field Curie temperature is close to that of the Gd-doped film.…”

“…This approach exploits an additional indirect exchange interaction, mediated via the conduction electrons supplied by the donors, that acts in addition to the direct Heisenberg exchange between the Eu 4f moments. 26,27 Because of the simplicity of this approach, many doping studies have been performed on single crystals 11,[15][16][17][18][19] and thin films. 8,[12][13][14][20][21][22][23][24][25] Despite exploiting the same physical mechanism to increase T C , the reported improvements vary strongly from experiment to experiment even for identical dopant elements and comparable dopant concentrations.…”

“…The doping concentration was chosen to be in the range of the maximum reported and theoretically predicted T F values. 15,16,[21][22][23]26,27,34,35 The dopants were chosen to provide a spectrum of ionic radii, electron configurations, and to investigate possible differences between magnetic (Gd) and non-magnetic (La, Lu) dopants. To analyze systematically changes originating from applied external magnetic fields, we kept film thickness, microstructure, and oxygen content constant.…”