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Register a new userModification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces
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The effect of gold capping on magnetic and transport properties of optimally doped manganite thin films is studied. An extraordinary suppression of conductivity and magnetic properties occurs in epitaxial (001) La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity increases by four orders of magnitude while the Curie temperature decreases by 180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant reduction of ferromagnetic double-exchange mechanism in manganite films upon the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic dead-layer at the Au/LSMO interface, associated with the creation of interfacial non double-exchange insulating phases.
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By using a realist microscopic model, we study the electric and magnetic properties of the interface between a half metallic manganite and an insulator. We find that the lack of carriers at the interface debilitates the double exchange mechanism, weakening the ferromagnetic coupling between the Mn ions. In this situation the ferromagnetic order of the Mn spins near the interface is unstable against antiferromagnetic CE correlations, and a separation between ferromagnetic/metallic and antiferromagnetic/insulator phases at the interfaces can occur. We obtain that the insertion of extra layers of undoped manganite at the interface introduces extra carriers which reinforce the double exchange mechanism and suppress antiferromagnetic instabilities.
Electrical conductivity, thermopower and magnetic properties of Fe-intercalated Fe0.33VSe2 has been reported between 4.2K - 300K. We observe a first order transition in the resistivity of the sintered pellets around 160K on cooling. The electronic properties including the transitional hysteresis in the resistance anomaly (from 80K-160K) are found to be very sensitive to the structural details of the samples, which were prepared in different annealing conditions. The thermopower results on the sintered pellets are reported between 10K - 300K. The magnetic measurements between 2K - 300K and up to 14 Tesla field show the absence of any magnetic ordering in Fe0.33VSe2. The magnetic moment per Fe -atom at room temperature (between 1.4 to 1.7 Bohr Magneton) is much lower than in previously reported anti-ferromagnetic FeV2Se4. Furthermore, the Curie constant shows a rapid and continuous reduction and combined with the high field magnetization result at 2K suggests a rapid decrease in the paramagnetic moments on cooling to low temperatures and the absence of any magnetic order in Fe0.33VSe2 at low temperatures.
Nanostructured La0.67Ca0.33MnO3 (NS-LCMO) was formed by pulsed-laser deposition on the surface of porous Al2O3. The resistance peak temperature (Tp) of the NS-LCMO increases with increasing average thickness of the films, while their Curie temperatures (Tc) remain unchanged. The coercive field of the samples increases with decreasing film thickness and its temperature dependence can be well described by Hc(T) = Hc(0)[1-(T/TB)1/2]. A large magnetoresistance and strong memory effect were observed for the NS-LCMO. The results are discussed in terms of the size effect, Coulomb blockade and magnetic tunneling effect. This work also demonstrates a new way to get nanostructured manganites.
Here we report the evolution of structural, magnetic and transport properties in MnBi$_{2-x}$Sb$_x$Te$_4$ (0$leq x leq$2) single crystals. MnSb$_2$Te$_4$, isostructural to MnBi$_2$Te$_4$, has the lattice parameters of textit{a}=4.2445(3)$AA$ and textit{c}=40.869(5)$AA$, respectively. With increasing Sb content in MnBi$_{2-x}$Sb$_x$Te$_4$, the textit{a}-lattice decreases linearly following the Vegards law while the textit{c}-lattice shows little compositional dependence. The textit{a}-lattice contraction occurs by reducing Mn-Te-Mn bond angle while Mn-Te bond length remains nearly constant. The anisotropic magnetic properties suggest an antiferromagnetic order below T$_N$=19,K for MnSb$_2$Te$_4$ with the magnetic moments aligned along the crystallographic textit{c}-axis. The antiferromagnetic ordering temperature slightly decreases from 24,K for MnBi$_2$Te$_4$ to 19,K for MnSb$_2$Te$_4$. More dramatic change was observed for the critical magnetic fields required for the spin-flop transition and moment saturation. With increasing Sb content, both critical fields decrease and in MnSb$_2$Te$_4$ a small field of 3,kOe is enough to saturate the moment. In high magnetic fields, the saturation moment shows significant suppression from 3.56$mu_B$/Mn for MnBi$_2$Te$_4$ to 1.57$mu_B$/Mn for MnSb$_2$Te$_4$. Data analyses suggest that both the interlayer magnetic interaction and single ion anisotropy decrease with increasing Sb content. The partial substitution of Bi by Sb also dramatically affects the transport properties. A crossover from n-type to p-type conducting behavior is observed around x=0.63. Our results show close correlation between structural, magnetic and transport properties in MnBi$_{2-x}$Sb$_x$Te$_4$ and that partial substitution of Bi by Sb is an effective approach to fine tuning both the magnetism and transport properties of MnBi$_{2-x}$Sb$_x$Te$_4$.
We have used oxygen ions irradiation to generate controlled structural disorder in thin manganite films. Conductive atomic force microscopy CAFM), transport and magnetic measurements were performed to analyze the influence of the implantation process in the physical properties of the films. CAFM images show regions with different conductivity values, probably due to the random distribution of point defect or inhomogeneous changes of the local Mn3+/4+ ratio to reduce lattice strains of the irradiated areas. The transport and magnetic properties of these systems are interpreted in this context. Metal-insulator transition can be described in the frame of a percolative model. Disorder increases the distance between conducting regions, lowering the observed TMI. Point defect disorder increases localization of the carriers due to increased disorder and locally enhanced strain field. Remarkably, even with the inhomogeneous nature of the samples, no sign of low field magnetoresistance was found. Point defect disorder decreases the system magnetization but doesn t seem to change the magnetic transition temperature. As a consequence, an important decoupling between the magnetic and the metal-insulator transition is found for ion irradiated films as opposed to the classical double exchange model scenario.
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