### Helena M. Petrilli (1)

**Ivan de P. Miranda(1), Ricardo N. Igarashi(1), Ângela B. Klautau(2)**

1 Departamento de Física dos Materiais e Mecânica, Instituto de Física, Universidade de São Paulo, 05508-090, São Paulo, SP, Brasil

2 Faculdade de Física, Universidade Federal do Pará, 66075-110, Belém, PA, Brasil

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## Magnetism of FexCo(1-x) nanoclusters on Pt(111): real-space investigation of dimensionality effects

Which magnetic properties change when we group Fe/Co atoms to form quasi-2D structures, in comparison with linear (quasi-1D) FexCo(1-x) arrangements? And how these properties react with the stoichiometry variation? Nanoscale transition metal materials have experienced a growing interest in the last decade, mostly due to the attractive properties for potential applications in magnetic recording devices. These behaviors can arise from the combination of broken inversion symmetry with spin-orbit coupling (SOC) and reduced dimensionality – which introduce complexities in the theoretical treatment. It is well known that a real-space method has the advantageous feature of lower computational cost in comparison with k-space formalisms, since the calculation time is linearly proportional to the number of inequivalent atoms in the system [1].

Therefore, in order to explore dimensionality effects, the magnetic properties of FexCo(1-x) clusters deposited on the Pt(111) surface are investigated using the Real Space Linear Muffin-Tin Orbital Atomic Sphere-Approximation (RS-LMTO-ASA) [1] method within the DFT framework. Several configurations, with different positions and Fe/Co concentrations, of triangular trimers and hexagonal heptamers are considered. We demonstrate the occurrence of a quadratic trend of the average orbital moments for trimers and heptamers with the Fe concentration, different from what was found for FexCo(1-x)/Pt(111) nanochains (linear) [3], but also contrasting to the monolayer (ML) behavior (nonlinear) [4]. Our results also show that the orbital moments change with local environment, especially for Co atoms, in agreement with previous investigations [5]. When the structures deposited on Pt(111) change from quasi-1D (Fe–Co nanowires) to quasi-2D arrangements, the average spin moments are still described by a linear function with respect to stoichiometry. Although all studied linear and compact FexCo(1-x) configurations are stable and substantially ferromagnetic, not all revealed a collinear magnetic ordering, presenting non-negligible Dzyaloshinskii-Moriya (DM) interactions. In addition, magnetic anisotropy energy (MAE) investigation of, the presented structures is discussed.

We thank CNPq, CAPES, FAPESP, CENAPAD, LCCA-USP and INCT-INEO.

[1] S. Frota-Pessôa and A. B. Klautau, Int. J. Mod. Phys. B 20, 5281 (2006).

[2] S. Frota-Pessôa, Phys. Rev. B 46, 14570 (1992).

[3] R. N. Igarashi et al., J. Phys. Condens. Matter 26, 206003 (2014).

[4] G. Moulas et al., Phys. Rev. B 78, 214424 (2008).

[5] C. Etz et al., Phys. Rev. B 75, 245432 (2007).