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Register a new userPerovskite-type cobalt oxide at the multiferroic Co/Pb Zr$_{0.2}$Ti$_{0.8}$O$_{3}$ interface
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Magnetic Tunnel Junctions whose basic element consists of two ferromagnetic electrodes separated by an insulating non-magnetic barrier have become intensely studied and used in non-volatile spintronic devices. Since ballistic tunnel of spin-polarized electrons sensitively depends on the chemical composition and the atomic geometry of the lead/barrier interfaces their proper design is a key issue for achieving the required functionality of the devices such as e.g. a high tunnel magneto resistance. An important leap in the development of novel spintronic devices is to replace the insulating barrier by a ferroelectric which adds new additional functionality induced by the polarization direction in the barrier giving rise to the tunnel electro resistance (TER). The multiferroic tunnel junction Co/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$/La$_{2/3}$Sr$_{1/3}$MnO$_3$ (Co/PZT/LSMO) represents an archetype system for which - despite intense studies - no consensus exists for the interface geometry and their effect on transport properties. Here we provide the first analysis of the Co/PZT interface at the atomic scale using complementary techniques, namely x-ray diffraction and extended x-ray absorption fine structure in combination with x-ray magnetic circular dichroism and ab-initio calculations. The Co/PZT interface consists of one perovskite-type cobalt oxide unit cell [CoO$_{2}$/CoO/Ti(Zr)O$_{2}$] on which a locally ordered cobalt film grows. Magnetic moments (m) of cobalt lie in the range between m=2.3 and m=2.7$mu_{B}$, while for the interfacial titanium atoms they are small (m=+0.005 $mu_{B}$) and parallel to cobalt which is attributed to the presence of the cobalt-oxide interface layers. These insights into the atomistic relation between interface and magnetic properties is expected to pave the way for future high TER devices.
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Among the recent discoveries of domain wall functionalities, the observation of electrical conduction at ferroelectric domain walls in the multiferroic insulator BiFeO3 has opened exciting new possibilities. Here, we report evidence of electrical conduction also at 180{deg} ferroelectric domain walls in the simpler tetragonal ferroelectric PZT thin films. The observed conduction shows nonlinear, asymmetric current-voltage characteristics, thermal activation at high temperatures and high stability. We relate this behavior to the microscopic structure of the domain walls, allowing local defects segregation, and the highly asymmetric nature of the electrodes in our local probe measurements.
The many surface reconstructions of (110)-oriented lanthanum--strontium manganite (La$_{0.8}$Sr$_{0.2}$MnO$_3$, LSMO) were followed as a function of the oxygen chemical potential ($mu_text{O}$) and the surface cation composition. Decreasing $mu_text{O}$ causes Mn to migrate across the surface, enforcing phase separation into A-site-rich areas and a variety of composition-related, structurally diverse B-site-rich reconstructions. The composition of these phase-separated structures was quantified with scanning tunneling microscopy (STM), and these results were used to build a 2D phase diagram of the LSMO(110) equilibrium surface structures.
5d iridates have shown vast emergent phenomena due to a strong interplay among its lattice, charge and spin degrees of freedom, because of which the potential in spintronic application of the thin-film form is highly leveraged. Here we have epitaxially stabilized perovskite SrIr$_{0.8}$Sn$_{0.2}$O$_3$ on [001] SrTiO$_3$ substrates through pulsed laser deposition and systematically characterized the structural, electronic and magnetic properties. Physical properties measurements unravel an insulating ground state with a weak ferromagnetism in the compressively strained epitaxial film. The octahedral rotation pattern is identified by synchrotron x-ray diffraction, resolving a mix of $a^+b^-c^-$ and $a^-b^+c^-$ domains. X-ray magnetic resonant scattering directly demonstrates a G-type antiferromagnetic structure of the magnetic order and the spin canting nature of the weak ferromagnetism.
The magnetic structure of the mixed antiferromagnet NdMn$_{0.8}$Fe$_{0.2}$O$_3$ was resolved. Neutron powder diffraction data definitively resolve the Mn-sublattice with a magnetic propagation vector ${bf k} = (000)$ and with the magnetic structure (A$_x$, F$_y$, G$_z$) for 1.6~K~$< T < T_N (approx 59$~K). The Nd-sublattice has a (0, f$_y$, 0) contribution in the same temperature interval. The Mn sublattice undergoes spin-reorientation transition at $T_1 approx 13$~K while the Nd magnetic moment keep ordered abruptly increases at this temperature. Powder X-ray diffraction shows a strong magnetoelastic effect at $T_N$ but no additional structural phase transitions from 2~K to 300~K. Density functional theory calculations confirm the magnetic structure of the undoped NdMnO$_3$ as part of our analysis. Taken together, these results show the magnetic structure of Mn-sublattice in NdMn$_{0.8}$Fe$_{0.2}$O$_3$ is a combination of the Mn and Fe parent compounds, but the magnetic ordering of Nd sublattice spans over broader temperature interval than in case of NdMnO$_3$ and NdFeO$_3$. This result is a consequence of the fact that the Nd ions do not order independently, but via polarization from Mn/Fe sublattice.
Atomistic effective Hamiltonian simulations are used to investigate electrocaloric (EC) effects in the lead-free Ba(Zr$_{0.5}$Ti$_{0.5}$)O$_{3}$ (BZT) relaxor ferroelectric. We find that the EC coefficient varies non-monotonically with the field at any temperature, presenting a maximum that can be traced back to the behavior of BZTs polar nanoregions. We also introduce a simple Landau-based model that reproduces the EC behavior of BZT as a function of field and temperature, and which is directly applicable to other compounds. Finally, we confirm that, for low temperatures (i.e., in non-ergodic conditions), the usual indirect approach to measure the EC response provides an estimate that differs quantitatively from a direct evaluation of the field-induced temperature change.
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