Magnetic trimer on non-magnetic substrate: From frustration towards non-collinearity

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Abstract
We present the very flrst non-collinear magnetic structure calculations of sup- ported metallic 3d triangular trimers. Within the vector Anderson model, in dependence on the ratio between hopping parameters in the trimer the ground state can be collinear or non-collinear. Calculations performed for the Cr and Fe trimers show that the modulus of the magnetic moments per atom are enhanced relatively to bulk value. The dependence, vs. hopping integrals, of the angles between the magnetic moments is difierent when going from Cr to Fe although these angles are equal to 120 degrees in the ground state of the equilateral triangle. Magnetic nanostructures on non-magnetic substrate has attracted recently large attention due to their novel and unusual properties important for the fundamental theory of magnetism as well as for the applications in the new electronic devices. Small magnetic clusters consisting of a few atoms have special interest because flrstly, they are the building blocks for epitaxial growth and secondly, they demonstrate very interesting behaviour which can be driven by changing the external conditions such as temperature or magnetic fleld. Such phenomena cannot be observed either for individual supported atoms due to the simplicity of the system or for the large (on atomic scale) objects like islands or monolayers due to the statistical averaging. The complex magnetic behaviour of small clusters is usually connected with the competition of several interactions and with the existence of several metastable states close in energy. The ground state can therefore be easily changed by external action and this could lead to the switching between difierent states, which give large modiflcation to the cluster's characteristics as, for example, huge increase of the total magnetic moment. Recently, Stepanyuk et al. (1) within ab initio KKR Green's function method have obtained four metastable collinear states with essentially difierent magnetic moments for 3d trimer- and