A. Antal, B. Lazarovits, L. Udvardi, L. Szunyogh, B. Újfalussy, P. Weinberger:

"First-principles calculations of spin interactions and the magnetic ground states of Cr trimers on Au(111)";

Physical Review B,77(2008), 1744291 - 1744298.

We present calculations of the magnetic ground states of Cr trimers in different geometries on top of a

Au 111 surface. By using a least squares fit method based on results obtained by means of a fully relativistic

embedded-cluster Greenīs function method, first we determined the parameters of a classical spin vector model

containing second- and fourth-order interactions. The developed method requires no a priori assumed symmetry

constraints; therefore, it is applicable throughout for small nanoparticles of arbitrary geometry. The magnetic

ground states were then found by solving the Landau-Lifshitz-Gilbert equations. In all cases considered,

the configurational energy of the Cr trimers is dominated by large antiferromagnetic nearest neighbor interactions,while the biquadratic spin interactions provide the second largest contributions to the energy.We find that an equilateral Cr trimer exhibits a frustrated 120° Néel type of ground state with a small out-of-plane component of the magnetization. Furthermore, we show that the Dzyaloshinsky-Moriya interactions determine the

chirality of the magnetic ground state. In cases of a linear chain and an isosceles trimer, collinear antiferromagnetic ground states are obtained with the magnetization lying parallel to the surface.\

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