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Ab initio investigations of magnetic properties of ultrathin transition ...

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72 4 Collinear magnetism <strong>of</strong> 3d-monolayers on Rh substrates<br />

Mn and Fe favor a c(2 × 2) antiferro<strong>magnetic</strong> (AFM) state, a checkerboard arrangement<br />

<strong>of</strong> up and down <strong>magnetic</strong> moments, on Rh(001) substrate. The Rh(111) substrate didn’t<br />

change the <strong>magnetic</strong> ground state but for Fe, where it changes from AFM on Rh(001) to<br />

FM on Rh(111). The <strong>magnetic</strong> anisotropy energies <strong>of</strong> these <strong>ultrathin</strong> <strong>magnetic</strong> films are<br />

calculated for the FM and the AFM states. With the exception <strong>of</strong> Cr and V, the easy axis<br />

<strong>of</strong> the magnetization is predicted to be in the film plane. To gain an understanding <strong>of</strong> the<br />

c(2 × 2) AFM state <strong>of</strong> Fe/Rh(100), we analyzed this result with respect to the trends <strong>of</strong><br />

the <strong>magnetic</strong> order <strong>of</strong> 3d monolayers on other 4d substrates, such as Pd(100) and Ag(100).<br />

The FM ground state <strong>of</strong> Fe monolayer on Rh(111) couldn’t be explained from the NM<br />

density <strong>of</strong> states and the Stoner model. In next chapter we will show our non-collinear<br />

calculations to predict Fe <strong>magnetic</strong> ground state on different hexagonal substrates. We will<br />

use a model Hamiltonian derived from the classical Heisenberg model to extract the exchange<br />

interaction parameters. The magnetocrystalline anisotropy (MCA) was calculated<br />

only for 3d/Rh(001). MCA <strong>of</strong> 3d/Rh(111) will be discussed separately in the last chapter.

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