Room temperature spin-polarization of EuS by thin ferromagnetic multilayers

For many years, scientists all over the world have been trying to find suitable materials for spintron-ic applications. In this respect, the europium chalcogenide europium sulfide (EuS) has very promising characteristics. First discovered and investigated in the 1960´s, it combines two very crucial properties: it is a semiconductor with E = 1.6 eV and has magnetic moment of 7 μ_B due to localized 4f electrons. The low Curie temperature of only 16,5 K, however, is a severe obstacle for room temperature application. In the 1990´s, an enhancement of the Curie temperature to about 160 K due to a proximity effect of Co was found for EuS nanocrystals embedded in a Co matrix. More recently, thin Co/EuS multilayers, where Co is polarizing the EuS layers, have shown a clear room temperature x-ray magnetic circular dichroism (XMCD) signal at the L₂ edge of EuS of about 0,5 μ_B, comparable to the magnetic moment of Ni. The samples were produced by e-beam evaporation in ultrahigh vacuum with EuS thicknesses between 2 and 4 nm. The growth of EuS on Co was investigated by high resolution cross section transmission electron microscopy, showing sharp interfaces. However, defects resulted in the formation of Eu₂S₃ where paramagnetic trivalent Eu³⁺ whit J = 0 is present.