Structure and magnetism in Fe/Fe_xPd_1−xcore/shell nanoparticles formed by alloying in Pd-embedded Fe nanoparticles

Abstract

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.

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…When analyzing the magnetic properties observed experimentally for diverse hard-soft core/shell nanoparticles a spread of different behaviors can be found [91][92][93][94][95][98][99][100][102][103][104]106,107,110,111,114,115,[121][122][123][125][126][127][128][129][130][131][132]136,140,141,143,175,. First, it should be pointed out that given that we are dealing with nanoparticles the core and shell sizes are rather small (i.e., usually smaller than 2 H ), thus, most of the systems exhibit smooth hysteresis loops typical of strongly exchange coupled hard-soft counterparts.…”

“…Similarly to pair-distribution function, EXAFS can give information on the local structure around a given element. For instance, Baker et al used EXAFS to study the degree of alloying in palladium-embedded iron nanoparticles, which results in Fe/Fe x Pd 1-x core/shell nanoparticles [175], whereas Gomes et al used it to investigate the cation distribution in ZnFe 2 O 4 /γ-Fe 2 O 3 core/shell nanoparticles [176].…”

“…With regard to core/shell nanoparticles, due to the increasing intensity of the electron scattering with increasing atomic number, Z [181], conventional bright-field TEM images may be useful in distinguishing the core from the shell only if the difference in average atomic composition is relatively large, as is the case for metal/metal oxide compositions or metals with at least one row of separation in the periodic table, as shown for instance in refs. [135,175,[182][183][184][185][186].…”

Biosynthesis of Fe, Pd, and Fe–Pd bimetallic nanoparticles and their application as recyclable catalysts for [3 + 2] cycloaddition reaction: a comparative approach

“…58 The small sized Pd NPs possessed a saturation magnetization of 15.79 emu g −1 . Considering the small sized Pd metallic particles on the surface of the iron core, the enhanced ferromagnetism of Fe-Pd NPs may be because of two phase magnetic systems 59 rather than Fe only. So the Fe-Pd NPs can be recovered easily by an external magnetic field.…”

Structure and magnetism in Cr-embedded Co nanoparticles

“…Atomic structure in nanoparticles can be changed pseudo-epitaxially by embedding them in a matrix of a different material, thereby potentially offering a degree of control over their magnetism. Atomic structure change has been reported in Fe and Co nanoparticles embedded in various matrices [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. A convenient way of embedding nanoparticles in a matrix, directly from the gas phase, is provided by the low energy cluster beam deposition (LECBD) method [22].…”