Non-collinear structure of Cr trimer on the surface of non-magnetic metals

Magnetic structure of Cr trimer clusters on non-magnetic metal substrate has been calculated by recursion method within Anderson model. The values of the moments are enhanced relatively to bulk bcc Cr due to the reduction of coordination number. Angles between the moments depend on the relations between hopping parameters V-ij, determined by the interatomic distance in the cluster. We performed systematic calculations of the ground state for different values of parameters V-12 = V-13 and V-23. For V-12 << V-23 ground state corresponds to moments on the atoms 2 and 3 with opposite direction, whereas the moment on atom 1 is perpendicular to them. For V-12 = V-23 the angle between each pair of moments equals 2 pi/3 and the total moment of the trimer is zero. A decrease of V-23 versus V-12 leads to collinear state with moment on the atom 1 antiparallel to the moments on second and third. Calculation in external magnetic field reveals the co-existence of two self-consistent states with essentially different total magnetic moments. In weak field these solutions are very close in energy whereas with the increase of the field the state with larger moment is stabilized. (C) 2000 Elsevier Science B.V. All rights reserved.