Room temperature ferromagnetism with large magnetic moment at low field in rare-earth-doped BiFeO₃thin films

Abstract

Thin films of rare earth (RE)-doped BiFeO3 (where RE=Sm, Ho, Pr and Nd) were grown on LaAlO3 substrates by using the pulsed laser deposition technique. All the films show a single phase of rhombohedral structure with space group R3c. The saturated magnetization in the Ho- and Sm-doped films is much larger than the values reported in the literature, and is observed at quite a low field of 0.2 T. For Ho and Sm doping, the magnetization increases as the film becomes thinner, suggesting that the observed magnetism is mostly due to a surface effect. In the case of Nd doping, even though the thin film has a large magnetic moment, the mechanism seems to be different.

Tuning Magnetic Properties of BiFeO3 Thin Films by Controlling Rare-Earth Doping: Experimental and First-Principles Studies

“…If impurities are more than 5% as resolution of the apparatus, one must see from XRD spectra (as we see that no alien peak other than BFO peaks in XRD data), but if they are less than 5%, then the contribution should not have been that big in magnitude. Some other group also got ferromagnetic ordering in Ho-doped BFO, however with much more modest magnitude, and the M s was obtained at a much greater field (as of 6 T) [12,14], while we got much a larger M s but at much lower field (as of 0.2 T). This makes a difference and it is quite meaningful for applications.…”

“…The peak of Fe 2p could be well observed at 711 eV for Fe 3+ and at 709.5 eV for Fe 2+ [14]. for the Pr and Nd cases [14].…”

“…This makes a difference and it is quite meaningful for applications. In comparison to those three dopants mentioned above, the Pr-and Nd-doped BFO films show much weaker magnetism: the curves in Figure 2 (a) show a much smaller magnitude for magnetization, and the curves of M(H) at room temperature are almost linear indicating a paramagnetic phase [14,30,31]. In order to identify the origin of magnetism of our films, XPS measurements were performed.…”

“…for the Pr and Nd cases [14]. The coexistence of Fe 2+ and Fe 3+ is thought to be in favor of the ferromagnetic phase in BFO films due to the double exchange between Fe 2+ and Fe 3+ via the role of oxygen as intermediates [32,33].…”

“…Thakuria and Joy had showed that the magnetic moment of the nanoparticles could be enhanced 3 times by substituting Bi by Ho. However, the reported saturated magnetization is still found only at a quite high field as of 6 T [12,14]. Partial substitution of Bi by Rare-Earth (RE) ions is known to induce a 4 ferromagnetic response which has been attributed to suppression of the spiral modulation [15,16].…”