X-ray magnetic circular dichroism in quasicrystals

The spectra of X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure (EXAFS) were measured in the ferromagnetic quasicrystals (a stable decagonal phase of Al₄₀Mn₂₅Fe₁₅Ge₂₀, a unstrained icosahedral phase of Al₅₀Pd₁₅Mn₂₀B₁₅, a strained icosahedral phase of Al_42.5Pd_7.5Mn₃₀B₂₀) and the orthorhombic approximant crystalline phase of Al₃₀Mn₄₀B₃₀. In Al₄₀Mn₂₅Fe₁₅Ge₂₀, the intensity of XMCD at Mn K-edge and Fe K-edge were -7×10^-5 and -5×10^-5, respectively, which are normalized by the edge jump of the normal absorption spectra. The values suggest that Mn and Fe in this alloy contribute to the magnetism to the same degree. From the result of EXAFS, the nearest neighbors of Mn atoms and Fe atoms were analyzed to be at the same distance. The environment around Mn and Fe were found not so similar except for the nearest neighbor distance. In Al₅₀Pd₁₅Mn₂₀B₁₅, Al_42.5Pd_7.5Mn₃₀B₂₀ and Al₃₀Mn₄₀B₃₀ alloys, the intensity of XMCD around the Mn K-edge were about -3×10^-4. The magnetic moments of Mn atoms in these alloys are roughly estimated to be 0.8 μ_B. The difference of a magnetic structure was detected between the quasicrystals and the approximant. The result of EXAFS analysis indicates that the distances from Mn to its first nearest neighbor and its second nearest neighbor are almost equal. The existence of phason strain field have no appreciable influence on the moment of Mn.