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Register a new userPressure induced magnetic phase separation in La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ manganite
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The pressure dependence of the Curie temperature T$_{C}(P)$ in La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ was determined by neutron diffraction up to 8 GPa, and compared with the metallization temperature T$_{IM}(P)$ cite{irprl}. The behavior of the two temperatures appears similar over the whole pressure range suggesting a key role of magnetic double exchange also in the pressure regime where the superexchange interaction is dominant. Coexistence of antiferromagnetic and ferromagnetic peaks at high pressure and low temperature indicates a phase separated regime which is well reproduced with a dynamical mean-field calculation for a simplified model. A new P-T phase diagram has been proposed on the basis of the whole set of experimental data.
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We demonstrate that magnetic phase separation and competing spin order in the colossal magnetoresistive (CMR) manganites can be directly explored via tuning strain in bulk samples of nanocrystalline La$_{1-x}$Ca$_x$MnO$_3$. Our results show that strain can be reversibly frozen into the lattice in order to stabilize coexisting antiferromagnetic domains within the nominally ferromagnetic metallic state of La$_{5/8}$Ca$_{3/8}$MnO$_3$. The measurement of tunable phase separation via magnetic neutron powder diffraction presents a direct route of exploring the correlated spin properties of phase separated charge/magnetic order in highly strained CMR materials and opens a potential avenue for realizing intergrain spin tunnel junction networks with enhanced CMR behavior in a chemically homogeneous material.
Using ultrafast optical spectroscopy, we show that polaronic behavior associated with interfacial antiferromagnetic order is likely the origin of tunable magnetotransport upon switching the ferroelectric polarity in a La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/BiFeO$_{3}$ (LCMO/BFO) heterostructure. This is revealed through the difference in dynamic spectral weight transfer between LCMO and LCMO/BFO at low temperatures, which indicates that transport in LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases in relatively high magnetic fields due to the increased spin alignment, while no discernible change is found in the LCMO film at low temperatures. These results thus shed new light on the intrinsic mechanisms governing magnetoelectric coupling in this heterostructure, potentially offering a new route to enhancing multiferroic functionality.
We report on a high-pressure Raman study on two members of the La$_{1-x}$Ca$_x$MnO$_{3-delta}$ manganite family ($x=0.20$, $delta=0$ and $delta=0.08$). The results obtained for the $delta=0$ sample show a different behavior in the low and high pressure regimes ascribed to the onset of a new pressure-activated interaction previously invoked in other manganite compounds. The comparison of our results with literature data gives further support to the identification of the Jahn-Teller active stretching mode and shows that pressure-induced octahedral symmetrization is more effective in systems exhibiting a lower metallic character. On the contrary the new interaction sets in at pressure which decreases on increasing the metallic character of the system indicating a relevant role of the Mn-Mn hopping integral in its activation.
We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which taken together suggest two spatially separated regions in close proximity possessing very different Mn-ion spin dynamics. One region corresponds to an extended cluster which displays critical slowing down near Tc and an increasing volume fraction below Tc. The second region possesses more slowly fluctuating spins and a decreasing volume fraction below Tc. These data are discussed in terms of the growth of small polarons into overlapping regions of correlated spins below Tc, resulting in a microscopically inhomogeneous FM transition.
We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measured in the temperature interval $4.2 ~mathrm{K} < T < 300 ~mathrm{K}$, for three concentrations $x = 0.52, 0.58$ and $0.75$ and in magnetic fields up to 5 T. The semiconductor/insulator--like behavior in zero field was observed in the entire temperature range for all three concentrations textit{x} and the electric conduction, at lower temperatures, in the CO state obeys 3D Motts variable--range hopping model. A huge negative magnetoresistance for $x = 0.52$ and $x = 0.58$, a metal--insulator transition for $B > 3 ~mathrm{T}$ for $x = 0.52$ and the presence of anisotropy in magnetoresistance for $x = 0.52$ and $x = 0.58$ show the fingerprints of colossal magnetoresistance (CMR) behavior implying the existence of ferromagnetic (FM) clusters. The declining influence of the FM clusters in the CO/AF part of the phase diagram with increasing $x$ contributes to a possible explanation that a phase coexistence is the origin of the CMR phenomenon.
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