Article

Textured growth of the high moment material Gd(0 0 0 1)/Cr(0 0 1)/Fe(0 0 1)

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Abstract

By magnetic coupling of Fe and Gd via Cr interlayers, the large local moment of Gd can be combined with the high Curie temperature of Fe. The textured growth of a Gd film is studied here by preparing trilayer systems of Fe/Cr/Gd on MgO(1 0 0) substrates by molecular-beam epitaxy (MBE). The thickness of the Cr interlayer was varied between 3 and 5 monolayers. The structural quality of the samples was confirmed by in situ RHEED and ex situ XRD measurements. Epitaxial Cr(0 0 1)/Fe(0 0 1) growth was observed, as expected. By use of 57Fe-CEMS (conversion electron Mössbauer spectroscopy) in combination with the 57Fe tracer layer method the Fe/Cr interface could be examined on an atomic scale and well separated Fe/Gd layers for all Cr thicknesses were confirmed. The unusual Gd/Cr crystallographic relationship of Gd(0 0 0 1)∥Cr(0 0 1), with domains of the hexagonal Gd basal planes randomly oriented in the sample plane and not in registry with the underlying Cr(0 0 1) lattice, was found from combined RHEED and x-ray measurements. Annealing of the samples resulted in a remarkable improvement of the crystalline structure of the Gd layers. On the other hand, the appearance of a single line in the CEM spectrum leads to the conclusion that during annealing a small amount of Fe diffuses into the Cr layer. The electronic structure and magnetism of this system are investigated by first-principles theory.

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... On the other hand, the formation of the bcc β-Gd phase in SiO 2 /Ta/Gd/Ta [14] systems was also reported. Studies in which only the hcp α-Gd phase is formed in Gd layers in Fe/Cr/Gd nanoheterogeneous structures [15] are also available. In our opinion, the data of [14,15] call for additional studies since the correctness of identification of Gd reflections in these studies is a question. ...
... Studies in which only the hcp α-Gd phase is formed in Gd layers in Fe/Cr/Gd nanoheterogeneous structures [15] are also available. In our opinion, the data of [14,15] call for additional studies since the correctness of identification of Gd reflections in these studies is a question. Since the magnetization of the fcc Gd phase (~22.2 ...
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The usefulness of Mössbauer spectroscopy for the investigation of magnetic multilayer systems is described. By applying 57Fe Mössbauer spectroscopy, the behavior of ultrathin magnetic layers, such as FCC-like Fe films on Cu(0 0 1), is studied. Position-specified (depth-selective) information is available by preparing samples in which monatomic 57Fe probe layers are placed at specific vertical positions, e.g. at interfaces or at the surface. As demonstrated for epitaxial chemically ordered Fe50Pt50 alloy films and polycrystalline nanostructured Tb/Fe multilayers, the Fe-spin structure can be determined directly, and a site-selective Fe-specific magnetic hysteresis loop can be traced in very-high-coercivity materials. For the studies of non-magnetic layers, on the other hand, hyperfine field observations by 197Au and 119Sn probes are worthwhile. Spin polarizations in Au layers penetrating from neighboring ferromagnetic 3D layers are estimated 197Au from Mössbauer spectra and are also studied by inserted 119Sn probes in Au/3D multilayers. In the Sn spectra for Cr/Sn multilayers, it was found that remarkably large spin polarization is penetrating into Sn layers from a contacting Cr layer, which suggests that Cr atoms in the surface layer have a ferromagnetic alignment.
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Polarized neutron reflectivity (PNR) measurements were used to determine the magnetic structure of a Gd/Cr multilayer grown by molecular beam epitaxy on a MgO (001) substrate. The nuclear structure of the multilayer was determined by X-ray reflectivity measurements. The PNR measurements show that the multilayer becomes magnetic below 200 K and below 100 K shows a hysteresis loop. In the fully magnetized state the magnetic moments of Gd and Cr layers align ferromagnetically and their mean layer values are 3.3 +/- 0.1 and 0.1 +/- 0.1 mu(B) per atom, respectively.
Article
We present ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local-density approximation at each molecular-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using subspace alignment. This approach avoids the instabilities inherent in quantum-mechanical molecular-dynamics calculations for metals based on the use of a fictitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows us to perform simulations over several picoseconds.
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