Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111) single crystal either by the reactive deposition of iron or oxidation of metallic iron monolayers. These films were characterized using low energy electron diffraction, scanning tunneling microscopy and conversion electron Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth of Fe 3 O 4 , in which the electronic and magnetic properties of the bulk material were modulated by superparamagnetic size effects for thicknesses below 2 nm, revealing specific surface and interface features. In contrast, the oxide films with FeO stoichiometry, which could be stabilized as thick as 4 nm under special preparation conditions, had electronic and magnetic properties that were very different from their bulk counterpart, wüstite. Unusual long range magnetic order appeared at room temperature for thicknesses between three and ten monolayers, the appearance of which requires severe structural modification from the rock-salt structure.
PACS: 68.47.Gh Oxide surfaces, 68.55.-a Thin film structure and morphology, 75.70.Ak Magnetic properties of monolayers and thin films, 81.15.-z Methods of deposition of films and coatings; film growth and epitaxy, 82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
We report on in-plane magnetic anisotropy in epitaxial bcc Co/Fe(110) bilayers on W(110). The magnetic surface anisotropy in the Co/Fe(110) bilayers exhibited a strong nonmonotonic dependence on Co coverage. Magneto-optical studies revealed a sharp maximum of the magnetic surface anisotropy, 2.44 mJ/m 2 , at d Co = 5Å. This giant interfacial magnetic anisotropy allowed a small fraction of a Co monolayer to reorient the magnetization of the bulk-like Fe film. We conclude that the mono-and double-layer bcc Co(110) exhibited in-plane magnetic anisotropy with a [110] easy axis.
Nuclear resonant scattering (NRS) of synchrotron radiation was used to investigate the magnetic anisotropy of iron films in MgO/Fe(t)/MgO(001) structures for t = (4–10) Å. The low-temperature NRS spectra were analyzed using a static magnetization model involving two interface-like components and a bulk-like component. We confirmed the existence of perpendicular magnetic anisotropy in MgO/Fe/MgO structures at 10 K with an increasing in-plane component of the magnetization for t > 8 Å over the entire thickness of the Fe film. The evolution of the magnetic structure with increasing temperature was studied for an Fe film thickness of 8.8 Å, and the temperature dependence of superparamagnetic fluctuations with characteristic frequencies ranging over tens of MHz was interpreted in terms of a spin reorientation transition. We showed that interfacial magnetic moments are less sensitive to thermal excitations than the magnetic moments in the film center, which was attributed to the spin pinning at the interface.
This comprehensive
work showcases two novel, rock-salt-type minerals
in the form of amphoteric cerium–tungstate double perovskite
and ilmenite powders created via a high-temperature solid-state reaction
in inert gases. The presented studies have fundamental meaning and
will mainly focus on a detailed synthesis description of undoped structures,
researching their possible polymorphism in various conditions and
hinting at some nontrivial physicochemical properties like charge
transfer for upcoming optical studies after eventual doping with selectively
chosen rare-earth ions. The formerly mentioned, targeted A
2
BB′X
6
group of compounds contains mainly divalent
alkali cations in the form of
XII
A = Ba
2+
, Ca
2+
sharing, here, oxygen-arranged clusters (
II
X
= O
2–
) with purposely selected central ions from
f-block
VI
B = Ce
4/3+
and d-block
VI
B′ = W
4/5/6+
since together they often possess
some exotic properties that could be tuned and implemented into futuristic
equipment like sensors or energy converters. Techniques like powder
XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and
TG were involved with an intent to thoroughly describe any possible
changes within these materials. Mainly, to have a full prospect of
any desirable or undesirable phenomena before diving into more complicated
subjects like: energy or charge transfer in low temperatures; to reveal
whether or not the huge angular tilting generates large enough dislocations
within the material’s unit cell to change its initial properties;
or if temperature and pressure stimuli are responsible for any phase
transitions and eventual, irreversible decomposition.
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