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Induced magnetic Cu moments and magnetic ordering in Cu2MnAl thin films on MgO(001) observed by XMCD

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The disorder–order transition of a highly defective A2-ordered Cu2MnAl film on MgO(0 0 1) upon annealing at 600 K was monitored by means of x-ray absorption spectroscopy (XAS) at the Cu and Mn L2,3 edges. Additionally, x-ray magnetic circular dichroism (XMCD) was employed to determine element-specific orbital and spin resolved magnetic moments of the Cu and Mn atoms. A small induced total magnetic moment of ≈0.04 ± 0.01μB per atom was detected at the Cu sites, whereas a total magnetic moment of 3.57 ± 0.52μB is carried by the Mn atoms. The experimental XAS and XMCD spectra of Cu agree reasonably with the results from ab initio calculations, magnetic moments derived by the sum rules are in accordance with the calculations.
Calculated (black and light grey curve) and experimental (dark grey curve) XAS (left) and XMCD (right) spectra of the Cu (top) and Mn (bottom) L 2,3 edges. The inset in graph (c) shows an enlargement of the L 3 edge of Mn and the inset in graph (b) shows the enlarged XMCD signal at the L 3 edge of Cu. For the calculations of disordered Cu 2 MnAl an exchange of 12.5% of the Mn atoms with Al atoms has been assumed. grey curve) with Mn ↓ −d states (figure 4(c), grey curve). Peak 2 comes from a hybridization of Cu ↑↓ −s and ↑↓ −d states (figure 4(d), black and grey curve) with those from Al (figure 4(b)). The shoulder (3) again is a result of an overlap of Cu and Al states, in this case the ↓ −p states are involved (figures 4(d) and (b) grey dashed curve). The element-specific magnetic moments obtained from calculations and a sum rule analysis of the experimental data are given in table 1. To determine magnetic moments via the sum rules, the number of the unoccupied d states (n) is needed. For our analysis we used the values from our band structure calculations n Mn = 4.49 and n Cu = 0.49. Applying the sum rules is problematic for Mn, because the initial j 3/2 , j 1/2 mixing at the L 3 and L 2 edge breaks the validity of the spin sum rule [20, 21]. As a first approximation, the spin magnetic moment obtained from the sum rules was multiplied by a factor of 1.5 [21] to correct for the jj mixing and obtain the real value of m S for Mn. From our sum rule analysis we obtained a spin magnetic moment of m S = 0.033 ± 0.01μ B and an orbital magnetic moment of m l = 0.009±0.001μ B per Cu atom. This results in a total magnetic moment of m tot = 0.042 ± 0.011μ B per Cu atom which is in good agreement with [23]. The error bar of the spin magnetic moment of Cu is large and arises
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... The experimental lattice constants are used for the present calculations; a ¼ 5:96, 6.06, and 6.38 Å for Cu 2 -MnAl, Ni 2 MnSn, and Pd 2 MnSn, respectively. [35][36][37] The LDA and QSGW calculations for band structures are performed with 20 Â 20 Â 20 and 6 Â 6 Â 6 q-point mesh, respectively. In the calculations of K "# and R "# , we use 24 Â 24 Â 24 q-point mesh. ...
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