Interplay between Chemical and Magnetic Order in FeRh Clusters

Abstract

The structure, chemical order, and magnetic behavior in small FeRh clusters having N ≤ 19 atoms have been investigated theoretically. For N ≤ 6 atoms, a thorough global geometry optimization is performed by considering all possible cluster topologies, while for 7 ≤ N ≤ 19 only a few representative structures are considered. In all cases, the starting structures are fully relaxed in the entire range of concentrations and spin polarizations. The calculations are based on a generalized-gradient approximation to density-functional theory. The results are analyzed systematically as a function of size and composition. The optimized cluster structures are compact with a clear tendency to maximize the number of nearest-neighbor FeRh pairs. For very small sizes, the low-lying isomers present usually a topology different from that of the optimal structure, while for larger clusters the lowest-energy isomerizations imply mainly changes in the chemical order. The most stable structures are in general ferromagnetic. Antiparallel spin arrangements are found in some low-lying isomers. An important enhancement of the local Fe moments is observed as result of Rh doping. This is shown to be a consequence of an increase in the number of Fe d holes due to Fe–Rh charge transfer. The local moments at the Rh atoms, which are significant already in small pure Rh clusters, are not strongly enhanced by Fe doping. Nevertheless, the overall stability of magnetism, as measured by the energy gained upon spin polarization, increases with Fe content. The influence of spin–orbit interactions on the cluster stability and spin order is discussed.

Cryokinetics and spin quenching in the N2 adsorption onto rhodium cluster cations

“…Our results are in line with an earlier study by Hamilton et al who reported similar stabilities of square-based pyramidal sp and trigonal bipyramidal tbp Rh 5 motifs in [Rh 5 (N 2 O)Ar] + clusters [41]. Other studies on various levels of theory on neutral and anionic rhodium clusters report similar results [26,43,[48][49][50][51]: low energy differences of nonet square pyramid 9 sp and trigonal bipyramid isomers tbp.…”

“…DFT modelling of [Rh 5 (N 2 O)Ar] + cluster complexes revealed a low energy difference of square-based pyramidal (sp) and trigonal bipyramidal (tbp) Rh 5 motifs beyond a definite assignment [41]. Other studies at various levels of theory report similar results on neutral and anionic rhodium clusters [26,43,[48][49][50][51]: There are low energy differences of nonet square pyramid and trigonal bipyramid isomers.…”

Structural formation of binary PtCu clusters: A density functional theory investigation

“…This fact opens the possibility for a wide range of technological applications, such as magnetic storage [7][8][9][10], and heterogeneous catalysis [2,[11][12][13][14]. This possibility, along with the novel and interesting properties found on those systems, motivated a large number of experimental and theoretical studies [15][16][17] focusing on binary TM clusters, such as PtPd [18,19], PdIr [20], PtNi [21], PtRh [22], FeRh [10,23], and PtCu [24][25][26][27][28], with the aim to understand the behaviour of their physical and chemical properties as a function of the number of atoms, compositions, structure, and charge states.…”

Spin and Orbital Magnetism in Free Nanoparticles

“…77,78 The optimized geometries are in general compact with a strong tendency to intermixing in order to maximize the number of FeRh nearest-neighbour (NN) bonds. A very rich variety of structural and magnetic behaviour has been revealed.…”