Time-dependent phenomena in phase-separated electron-doped manganites

D. Niebieskikwiat, J. Tao, J. M. Zuo, and M. B. Salamon

Phys. Rev. B 78, 014434 – Published 31 July 2008

Abstract

We present time-dependent behavior of the transport and magnetic properties in electron-doped manganites. The relaxation of the electrical resistivity $(ρ)$ shows a clear correlation with the microscopic properties of the samples observed through transmission electron microscopy. Two different relaxation mechanisms could be distinguished in ${La}_{0.23} {Ca}_{0.77} {MnO}_{3}$ . One of them was found to be common to different electron-doped manganites and is associated with a defective formation of the charge-order (CO) phase. The second one is the result of the coexistence of the CO phase with a secondary charge-disordered (CD) phase. In this case, a low-temperature boundary between static and dynamic phase-separation regimes is determined by the appearance of a small ferromagnetic moment associated with the CD volume. These results show that kinematic constraints and magnetoelastic interactions are key ingredients for a proper understanding of phase-separated manganites.

Received 17 October 2007

DOI:https://doi.org/10.1103/PhysRevB.78.014434

Authors & Affiliations

D. Niebieskikwiat^1,2, J. Tao^3,*, J. M. Zuo³, and M. B. Salamon^1,†

¹Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
²Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Quito, Ecuador
³Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

^*Present address: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
^†Present address: School of Natural Sciences and Mathematics, The University of Texas at Dallas, Richardson, TX 75083, USA.

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Vol. 78, Iss. 1 — 1 July 2008

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Images

Figure 1
(Color online) Resistivity as a function of time at $T = 90 K$ for the ${La}_{1 - x} {Ca}_{x} {MnO}_{3}$ samples. The solid line shows the logarithmic behavior for $x = 2 / 3$ . Inset: temperature dependence of $ρ$ for the same samples.Reuse & Permissions
Figure 2
(Color online) Temperature dependence of the logarithmic relaxation rate of the resistivity, $S = d (log ρ) / d (log t)$ , for the ${La}_{1 - x} {Ca}_{x} {MnO}_{3}$ samples (open triangles for $x = 0.77$ and open circles for $x = 2 / 3$ ). We also include $S (T)$ for ${Pr}_{1 / 3} {Ca}_{2 / 3} {MnO}_{3}$ (labeled as PCMO, solid diamonds). The labels ‘‘static PS’’ and ‘‘dynamic PS’’ refer to the different relaxation regimes for the sample $x = 0.77$ in its phase-separated state, while “pure CO” indicates a pure charge-order phase. $T_{C}$ indicates the low-temperature boundary between the static and dynamic PS regimes for $x = 0.77$ . This temperature coincides with the appearance of a small FM moment in the sample. Below $T^{*}$ the positive relaxation rate for ${La}_{1 / 3} {Ca}_{2 / 3} {MnO}_{3}$ and ${Pr}_{1 / 3} {Ca}_{2 / 3} {MnO}_{3}$ rapidly decreases, indicating the freezing of the motion of defects within the CO phase.Reuse & Permissions
Figure 3
(Color online) From electron-diffraction experiments we obtained the charge-order superlattice reflections (SLRs) around the (204) fundamental spot. This figure presents the time dependence of the peak intensity of these SLRs for the ${La}_{0.23} {Ca}_{0.77} {MnO}_{3}$ sample $(x = 0.77)$ at $T = 176 K$ . The inset shows that at a similar temperature (170 K) the resistivity also increases with time, as it does in ${La}_{1 / 3} {Ca}_{2 / 3} {MnO}_{3}$ $(x = 2 / 3)$ and ${Pr}_{1 / 3} {Ca}_{2 / 3} {MnO}_{3}$ (PCMO).Reuse & Permissions
Figure 4
(Color online) Magnetization vs temperature for ${La}_{0.23} {Ca}_{0.77} {MnO}_{3}$ measured on warming after cooling using the procedure shown in the sketch (see below). The magnetic transition at $T_{C} \sim 64 K$ triggers a crossover between the static and dynamic phase-separation (PS) regimes. Cooling procedure (follow the direction of the arrows): (1) the sample is cooled from 300 to 90 K at 4 K/min with an applied magnetic field $H = 100 Oe$ , (2) the sample is kept at 90 K for a period $t_{w}$ (the waiting time), (3) cooling to 10 K is resumed, and (4) $M$ vs $T$ is measured for different values of $t_{w}$ , as shown in the main panel.Reuse & Permissions
Figure 5
Magnetic moment of the ${La}_{0.23} {Ca}_{0.77} {MnO}_{3}$ sample as a function of $t_{w}$ (the time waited at $T = 90 K$ during the cooling process, see Fig. 4). For $T = 10 K$ (lower than $T_{C} \sim 64 K$ ) there is a clear increase in the magnetic moment with $t_{w}$ , as opposed to the case $T = 100 K$ .Reuse & Permissions
Figure 6
(Color online) For temperatures close to $T_{C} \sim 64 K$ the temporal evolution of the electrical resistivity of ${La}_{0.23} {Ca}_{0.77} {MnO}_{3}$ shows a curious peak, related to the competition of two different relaxation mechanisms. Inset: for temperatures at either side of $T_{C}$ a single relaxation mechanism is observed ( $ρ$ increases with time for $T < T_{C}$ and decreases with time for $T > T_{C}$ ).Reuse & Permissions

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