Epitaxial thin films of binary Eu-compounds close to a valence transition

Strain-induced magnetic anisotropy of multi-domain epitaxial EuPd2 thin films

“…From temperature-dependent resistivity data we could confirm a phase transition at about 72 K (see figure 1(b)), which we attributed to the onset of ferromagnetic order. This was further corroborated by Hall effect and magnetoresistance measurements [7]. An important consequence of the combined effects of lattice symmetry differences at the substrate-thin-film interface and weak thin-film substrate interaction, we observed an island growth mode with multiple growth domains; see below in figures 2(a) and (b).…”

“…To this end, the Eu and Pd flux rates were adjusted using a quartz crystal microbalance to yield the required stoichiometry. According to the results of the growth of epitaxial thin films of EuPd3 on MgO (100) substrates, Eu desorption due to the high substrate temperature plays a major role during preparation of Eu-based films, see [7]. This so called MBE-or Eu-distillation effect also occurs during the formation of stoichiometric EuO thin films for sufficiently high growth temperatures and with a chemically inert substrate at a low oxygen partial pressure [8].…”

“…According to the SEM investigation (see figure 2(a)) well defined faceted islands on a lateral length scale of about 100 nm develop, thus corroborating the multi-domain results from the asymmetric x-ray scans. Further details regarding the microstructure and the magnetotransport properties can be found in [7].…”

“…Intermetallic Eu-compounds are an interesting class of materials due to the sensitivity of the Eu valence state to the available volume at the respective lattice sites. Eu can have two possible valence states; magnetic divalent Eu 2+ (4f 7 ) Eu(II) with a total angular momentum of J = 7/2 and non-magnetic trivalent Eu 3+ (4f 6 ) Eu(III) with J = 0. As a function of temperature, strain, or pressure, a number of Eu-based compounds undergo a valence crossover accompanied by significant volume changes due to the strong coupling of lattice and spin degrees of freedom [1,2].…”

“…In a recent publication we presented results on the epitaxial thin film growth of the binary Eu-compounds EuPd 3 and EuPd 2 onto MgO (100) substrates by means of MBE [7]. In that work we focused on the growth preferences and epitaxial relationships, as well as on the structural and temperature-dependent magnetotransport properties of the thin films.…”