Fe-induced magnetization of Pd: The role of modified Pd surface states

Graded magnetic materials

Graded magnetic materials represent a promising new avenue in modern material science from both fundamental and application points of view. Over the course of the last few years, remarkable results have been obtained in (epitaxial) heterostructures based on thin alloy films featuring diverse compositional depth profiles. As a result of the precise tailoring of such profiles, the exchange coupling, and the corresponding effective or local Curie temperatures can be controlled over tens of nm with an excellent precision. This topical review article reports the most recent advances in this emerging research field. Several aspects are covered, but the primary focus lies in the study of compositional gradients being transferred into depth dependent magnetic states in ferromagnets, while also reviewing other experimental attempts to create exchange graded films and materials in general. We account for the remarkable progress achieved in each sample and composition geometry by reporting the recent developments and by discussing the research highlights obtained by several groups. Finally, we conclude the review article with an outlook on future challenges in this field.

Structure and magnetism in Fe/FexPd1-x core/shell nanoparticles formed by alloying in Pd-embedded Fe nanoparticles

We have investigated atomic structure and magnetism in Fe nanoparticles with a diameter of 2 nm embedded in a Pd matrix. The samples for these studies were prepared directly from the gas phase by co-deposition, using a gas aggregation source and an MBE-type source for the Fe nanoparticles and Pd matrix respectively. Extended absorption fine structure (EXAFS) measurements indicate that there is an appreciable degree of alloying at the nanoparticle/matrix interface; at dilute nanoparticle concentrations, more than half of the Fe atoms are alloyed with Pd. This leads to a core/shell structure in the embedded nanoparticles, with an FexPd1-x shell surrounding a reduced pure Fe core. Magnetism in the nanocomposite samples was probed by means of magnetometry measurements, which were interpreted in the light of their atomic structure. These point to a magnetized cloud of Pd atoms surrounding the embedded nanoparticles which is significantly larger than around single Fe atoms in Pd. The coercivities in the Fe/Pd nanocomposite samples are larger than in FexPd1-x atomic alloys of corresponding composition, which is consistent with exchange coupling between the magnetically harder and softer regions in the nanocomposite samples.

The magnetic proximity effect in a ferrimagnetic Fe3O4 core/ferrimagnetic γ-Mn2O3 shell nanoparticle system

We report the magnetic proximity effect in a ferrimagnetic Fe(3)O(4) core/ferrimagnetic γ-Mn(2)O(3) shell nanoparticle system, in terms of an enhancement of the Curie temperature (T(c)) of the γ-Mn(2)O(3) shell (~66 K) compared to its bulk value (~40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K). The ferrimagnetic nature of both core and shell has been found from a neutron diffraction study. The origin of these two features of the magnetic proximity effect has been ascribed to the proximity of the γ-Mn(2)O(3) shell with a high-T(c) Fe(3)O(4) core (~858 K in bulk form) and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of the magnetic proximity effect and the exchange bias phenomenon in a single system.

Enhanced magnetic moment in Fe-doped Pd(n) clusters (n = 1-13): a density functional study

Here we report a systematic theoretical study of the equilibrium structures, electronic and magnetic properties of FePd(n-1) clusters with n = 1-13, within the framework of density functional theory. The results show that the doping of a single Fe impurity enhances the binding energies as well as the magnetic moment of the Pd(n) clusters. Interestingly, in the mid-size region (n = 5-7), Fe substitution in Pd(n) clusters results in a three fold enhancement in the magnetic moment. We find that the geometries of the host clusters do not change significantly after the addition of an Fe atom, except for n = 6, 7, 11, 12. In the lowest energy configurations, the Fe atom tries to increase its coordination number by moving from the convex to the interior site as the number of Pd atoms varies from 2 to 12.

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.