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Register a new userEffect of A-site ionic radius on metamagnetic transition in charge ordered $Sm_{0.5}(Ca_{0.5-y}Sr_{y})MnO_3$ compounds
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We investigate the ultra-sharp jump in the isothermal magnetization and the resistivity in the polycrystalline $Sm_{0.5}(Ca_{0.5-y}Sr_{y})MnO_3$ $(y = 0, 0.1, 0.2, 0.25, 0.3, 0.5)$ compounds. The critical field $(H_{cr})$, required for the ultra-sharp jump, decreases with increase of `Sr concentration, i.e. with increase of average A-site ionic radius $langle r_Arangle$. The magnetotransport data indicate that the phase separation increases with the increase of $langle r_Arangle$, i.e. with $y$. The dependency of $H_{cr}$ with magnetic field sweep rate reveals that the ultra-sharp jump from antiferromagnetic (AFM) state to the ferromagnetic (FM) state is of martensitic in nature. Our two-band double exchange model Hamiltonian calculations show that the `Sr doping induces the ferromagnetic clusters in the antiferromagnetic insulating phase and in turn reduces the critical field. In the end we present a phenomenological picture obtained from our combined experimental and theoretical study.
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Large magnetoresistive materials are of immense interest for a number of spintronic applications by developing high density magnetic memory devices, magnetic sensors and magnetic switches. Colossal magnetoresistance, for which resistivity changes several order of magnitude (${sim10^4 %}$) in an external magnetic field, occurs mainly in phase separated oxide materials, namely manganites, due to the phase competition between the ferromagnetic metallic and the antiferromagnetic insulating regions. Can one further enhance the magnetoresistance by tuning the volume fraction of the two phases? In this work, we report a huge colossal magnetoresistance along with the ultra-sharp metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$ manganite compound by suitably tuning the volume fraction of the competing phases. The obtained magnetoresistance value at 10 K is as large as $sim10^{13}%$ in a 30 kOe external magnetic field and $sim10^{15}%$ in 90 kOe external magnetic field and is several orders of magnitude higher than any other observed magnetoresistance value reported so far. Using model Hamiltonian calculations we have shown that the inhomogeneous disorder, deduced from tunneling electron microscopy, suppresses the CE-type phase and seeds the ferromagnetic metal in an external magnetic field.
Titanates with the perovskite structure, including ferroelectrics (e.g., BaTiO$_3$) and ferromagnetic ones (e.g., YTiO$_3$), are important functional materials. Recent theoretical studies predicted multiferroic states in strained EuTiO$_3$ and titanate superlattices, the former of which has already been experimental confirmed. Here, a first-principles calculation is performed to investigate the structural, magnetic, and electronic properties of Y half-substituted LaTiO3. Our results reveal that the magnetism of Y$_{0.5}$La$_{0.5}$TiO$_3$ sensitively depends on its structural details because of the inherent phase competition. The lowest energy state is the ferromagnetic state, resulting in 0.25 $mu_{rm B}$/Ti. Furthermore, some configurations of Y$_{0.5}$La$_{0.5}$TiO$_3$ exhibit hybrid improper polarizations, which can be significantly affected by magnetism, resulting in the multiferroic properties. Because of the quenching disorder of substitution, the real Y$_{0.5}$La$_{0.5}$TiO3 material with random A-site ions may exhibit interesting relaxor behaviors.
We report a detailed study of the electric transport and magnetic properties of the LaNdCaMnO manganite system. Substitution of LaIII by smaller NdIII ions, reduces the mean ionic radius of the A site ion. We have studied samples in the entire range between rich La and rich Nd compounds. Results of DC magnetization and resistivity show that doping destabilize the FM character of the pure La compound and triggers the formation of a phase separated state at intermediate doping. We have also found evidence of a dynamical behaviour within the phase separated state. A phase diagram is constructed, summarizing the effect of chemical substitution on the system.
The temperature dependence of ultrafast photoinduced reflectivity transients is reported in Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ thin film. The photoinduced reflectivity shows a complex response with very different temperature dependences on different timescales. The response on the sub-ps timescale appears to be only weakly sensitive to the 270K-metal-insulator phase transition. Below $sim 160$ K the sub-ps response displays a two component behavior indicating inhomogeneity of the film resulting from the substrate induced strain. On the other hand, the slower response on the 10-100 ps timescale is sensitive only to the metal-insulator phase transition and is in agreement with some previously published results. The difference in the temperature dependences of the responses on nanosecond and $mu $s timescales indicates that thermal equilibrium between the different degrees of fredom is established relatively slowly - on a nanosecond timescale.
We have studied the critical behaviour in $La_{0.5}Sr_{0.5}CoO_{3}$ near the paramagnetic-ferromagnetic transition temperature. We have analysed our dc magnetisation data near the transition temperature with the help of modified Arrott plots, Kouvel-Fisher method. We have determined the critical temperature $T_c$ and the critical exponents, $beta$ and $gamma$. With these values of $T_c$, $beta$ and $gamma$, we plot $M/(1-T/T_c)^{beta}$ vs $H/(1-T/T_c)^{gamma}$. All the data collapse on one of the two curves. This suggests that the data below and above $T_c$ obeys scaling, following a single equation of state.
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