Magnetism of epitaxial fcc: Iron films on Cu(001) investigated by spin-polarized photoelectron emission

Magnetic ground state of face-centered-cubic structure of iron

First principles calculations reveal that the antiferromagnetic double layer (AFMD) along the magnetization direction of 〈0 0 1〉 is the magnetic ground state of face-centered-cubic (FCC) structure of iron (Fe) due to its lowest total energy among all the studied magnetic states. This magnetic ground state of AFMD-〈0 0 1〉 is fundamentally due to a stronger chemical bonding in terms of electronic structure, and could be confirmed by its mechanical properties for the first time. Calculations also show that lattice constant has an important effect to determine the magnetic state of FCC Fe, and a transition of magnetic state between AFMD-〈0 0 1〉 and ferromagnetic happens at the critical lattice constant of 3.666 Å. The derived results are in good agreement with experimental and theoretical observations, and could clarify the controversy regarding magnetic ground state of FCC Fe in the literature.

Microscopic analysis of the composition driven spin-reorientation transition in Ni(x)Pd(1-x)/Cu(001)

The spin-reorientation transition (SRT) in epitaxial NixPd1-x/Cu(001) is studied by photoemission microscopy utilizing the X-ray magnetic circular dichroism effect at the Ni L2,3 edge. In a composition/thickness wedged geometry, a composition driven SRT could be observed between 37 ML and 60 ML, and 0 and 38% of Pd. Microspectroscopy in combination with azimuthal sample rotation confirms a magnetization preference changing from the [001] to an in-plane easy axis. At this increased thickness, the domain patterns arrange comparable to SRTs in ultrathin films. The images document domains equivalent to a canted state SRT, at which an additional effect of in-plane anisotropies could be identified.

Temperature Dependence of Two-Dimensional Spin Anisotropies

Large anisotropy energy is an essential property of high quality permanent magnets. In previous work we have calculated the spin polarized electronic structure and anisotropy of monolayers and slabs of Fe, Ni, and V. In this work we calculate the dependence on temperature of the spin anisotropy of a ferromagnetic monolayer of Fe. We find the easy direction of magnetization is not sensitive to the temperature; the variations calculated here are likely too small to be observed. It is perpendicular to the plane of the surface for both low and high temperatures. The calculations become progressively more ill-behaved as the temperatures are lowered and require more computer time for satisfactory convergence.

For Fe/Cu {100}, we find the spins always prefer to point out of plane. Experimental results in general are consistent with this view, although the systems seem to be difficult to prepare.

Comparison of the Magnetic Properties of Metastable Hexagonal Close-Packed Ni Nanoparticles with Those of the Stable Face-Centered Cubic Ni Nanoparticles

We report the first magnetic study of pure and metastable hexagonal close-packed (hcp) Ni nanoparticles (sample 1). We also produced stable face-centered cubic (fcc) Ni nanoparticles, as mixtures with the hcp Ni nanoparticles (samples 2 and 3). We compared the magnetic properties of the hcp Ni nanoparticles with those of the fcc Ni nanoparticles by observing the evolution of magnetic properties from those of the hcp Ni nanoparticles to those of the fcc Ni nanoparticles as the number of fcc Ni nanoparticles increased from sample 1 to sample 3. The blocking temperature (T(B)) of the hcp Ni nanoparticles is approximately 12 K for particle diameters ranging between 8.5 and 18 nm, whereas those of the fcc Ni nanoparticles are 250 and 270 K for average particle diameters of 18 and 26 nm, respectively. The hcp Ni nanoparticles seem to be antiferromagnetic for T < T(B) and paramagnetic for T > T(B). This is very different from the fcc Ni nanoparticles, which are ferromagnetic for T < T(B) and superparamagnetic for T > T(B). This unusual magnetic state of the metastable hcp Ni nanoparticles is likely related to their increased bond distance (2.665 angstroms), compared to that (2.499 angstroms) of the stable fcc Ni nanoparticles.

Body-centered-cubic Ni and its magnetic properties

The body-centered-cubic (bcc) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bcc Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52+/-0.08 micro(B)/atom. The cubic magnetocrystalline anisotropy of bcc Ni is determined to be +4.0x10(5) ergs x cm(-3), as opposed to -5.7x10(4) ergs x cm(-3) for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bcc Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation.