6 research outputs found
Epitaxial thin films of binary Eu-compounds close to a valence transition
Intermetallic binary compounds of europium reveal a variety of interesting
phenomena due to the interconnection between two different magnetic and 4f
electronic (valence) states, which are particularly close in energy. The
valence states or magnetic properties are thus particularly sensitive to
strain-tuning in these materials. Consequently, we grew epitaxial EuPd
(magnetic Eu) and EuPd (nonmagnetic Eu) thin films on
MgO(001) substrates using molecular beam epitaxy. Ambient X-ray diffraction
confirms an epitaxial relationship of cubic Laves-type (C15) EuPd with an
(111)-out-of plane orientation, whereby four distinct in-plane crystallographic
domains develop. For simple cubic EuPd two different out-of-plane
orientations can be obtained by changing the substrate annealing temperature
under ultra-high vacuum conditions from 600{\deg} C to 1000{\deg} C for one
hour. A small resistance minimum evolves for EuPd thin films grown with low
temperature substrate annealing, which was previously found even in single
crystals of EuPd and might be attributed to a Kondo or weak localization
effect. Absence of influence of an applied magnetic fields and magnetotransport
measurements suggest always a nonmagnetic ground state for EuPd thin films,
i. e., a purely trivalent Eu valence, as previously found in EuPd3 single
crystals. For EuPd magnetic ordering below ~72 K is observed, quite similar
to single crystal behaviour. Additional field dependent measurements of the
magnetoresistance and the Hall effect show hysteresis effects below ~0.4 T and
an anomalous Hall effect below ~70 K, which saturates around 1.4 T, thus
proving a ferromagnetic ground state of the divalent Eu
Magnetic properties of multi-domain epitaxial EuPd thin films
Europium intermetallic compounds show a variety of different ground states
and anomalous physical properties due to the interactions between the localized
4f electrons and the delocalized electronic states. Europium is also the most
reactive of the rare earth metals which might be the reason why very few works
are concerned with the properties of Eu-based thin films. Here we address the
low-temperature magnetic properties of ferromagnetic EuPd thin films
prepared by molecular beam epitaxy. The epitaxial (111)-oriented thin films
grow on MgO (100) with eight different domain orientations. We analyze the
low-temperature magnetic hysteresis behavior by means of micromagnetic
simulations taking the multi-domain morphology explicitly into account and
quantify the magnetic crystal anisotropy contribution. By ab initio
calculations we trace back the microscopic origin of the magnetic anisotropy to
thin film-induced biaxial strain
Strain-induced magnetic anisotropy of multi-domain epitaxial EuPd2 thin films
Europium intermetallic compounds show a variety of different ground states and anomalous physical properties due to the interactions between the localized 4f electrons and the delocalized electronic states. Europium is also the most reactive of the rare earth metals which might be the reason why very few works are concerned with the properties of Eu-based thin films. Here we address the low-temperature magnetic properties of ferromagnetic EuPd _2 thin films prepared by molecular beam epitaxy. The epitaxial (111)-oriented thin films grow on MgO (100) with eight different domain orientations. We analyze the low-temperature magnetic hysteresis behavior by means of micromagnetic simulations taking the multi-domain morphology explicitly into account and quantify the magnetic crystal anisotropy contribution. By ab initio calculations we trace back the microscopic origin of the magnetic anisotropy to thin film-induced uniform biaxial strain
Vanadium and Manganese Carbonyls as Precursors in Electron-Induced and Thermal Deposition Processes
The material composition and electrical properties of nanostructures obtained from focused electron beam-induced deposition (FEBID) using manganese and vanadium carbonyl precursors have been investigated. The composition of the FEBID deposits has been compared with thin films derived by the thermal decomposition of the same precursors in chemical vapor deposition (CVD). FEBID of V(CO)6 gives access to a material with a V/C ratio of 0.63–0.86, while in CVD a lower carbon content with V/C ratios of 1.1–1.3 is obtained. Microstructural characterization reveals for V-based materials derived from both deposition techniques crystallites of a cubic phase that can be associated with VC1−xOx. In addition, the electrical transport measurements of direct-write VC1−xOx show moderate resistivity values of 0.8–1.2 × 103 µΩ·cm, a negligible influence of contact resistances and signatures of a granular metal in the temperature-dependent conductivity. Mn-based deposits obtained from Mn2(CO)10 contain ~40 at% Mn for FEBID and a slightly higher metal percentage for CVD. Exclusively insulating material has been observed in FEBID deposits as deduced from electrical conductivity measurements. In addition, strong tendencies for postgrowth oxidation have to be considered
Clamping effect on temperature-induced valence transition in epitaxial EuPdSi thin films grown on MgO(001)
Bulk EuPdSi show a temperature-driven valence transition of europium from ∼+2 above 200 K to ∼+3 below 100 K, which is correlated with a shrinking by approximately 2% of the tetragonal crystal lattice along the two a-axes. Due to this interconnection between lattice and electronic degrees of freedom the influence of strain in epitaxial thin films is particularly interesting. Ambient x-ray diffraction (XRD) confirms an epitaxial relationship of tetragonal EuPdSi on MgO(001) with an out-of plane c-axis orientation for the thin film, whereby the -axes of both lattices align. XRD at low temperatures reveals a strong coupling of the thin film lattice to the substrate, showing no abrupt compression over the temperature range from 300 to 10 K. Hard x-ray photoelectron spectroscopy at 300 and 20 K reveals a temperature-independent valence of +2.0 for Eu. The evolving biaxial tensile strain upon cooling is suggested to suppress the valence transition. Instead temperature-dependent transport measurements of the resistivity and the Hall effect in a magnetic field up to 5 T point to a film thickness independent phase transition at 16 to 20 K, indicating magnetic ordering
Figure 4
Post mortem characterization of ISA aerogel derived oxide and methanol pulse experiment on ISA aerogel derived oxide and V2O