Showing papers on "Colossal magnetoresistance published in 1996"
TL;DR: In this paper, the magnetoresistance and the field dependent magnetization have been systematically examined in the low temperature ferromagnetic metallic state of single crystal and polycrystalline.
Abstract: The magnetoresistance (MR) and the field dependent magnetization have been systematically examined in the low temperature ferromagnetic metallic state of single crystal and polycrystalline ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$. We find that the intrinsic negative MR in single crystal is due to the suppression of spin fluctuations, and magnetic domain boundaries do not dominate the scattering process. In contrast, we demonstrate that the MR in the polycrystalline samples exhibits two distinct regions: large MR at low fields dominated by spin-polarized tunneling between grains and high field MR which is remarkably temperature independent from 5 to 280 K.
1,594 citations
TL;DR: A model which incorporates the physics of dynamic Jahn-Teller and double-exchange effects is presented and solved via a dynamical mean field approximation to reproduce the behavior of the resistivity and magnetic transition temperature observed in Sr_x MnO_3.
Abstract: A model for the doped rare-earth manganites such as ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ incorporating the physics of dynamic Jahn-Teller and double-exchange effects is presented and solved via a dynamical mean field approximation. The interplay of these two effects as the electron phonon coupling is varied reproduces the observed behavior of the resistivity and magnetic transition temperature.
1,041 citations
TL;DR: It is shown that the resistivity decreases with increasing applied magnetic field because the spin-dependent tunneling increases as the relative orientation of the magnetization between grains becomes parallel.
Abstract: A mechanism for the large magnetoresistance observed recently in Co-Al-O granular magnetic films is presented. It is shown that the resistivity decreases with increasing applied magnetic field because the spin-dependent tunneling increases as the relative orientation of the magnetization between grains becomes parallel. With this mechanism we are able to account for the dependence of the magnetoresistance on the magnetization and temperature.
366 citations
NEC1
TL;DR: In this paper, the giant magnetoresistance (GMR) was observed in Ti2Mn2O7, which has a pyrochlore structure and thus differs both structurally and electronically from perovskites.
Abstract: MATERIALS exhibiting giant magnetoresistance (GMR) undergo a large change in electrical resistance in response to an applied magnetic field. This effect is of technological interest as it can be exploited for the sensitive detection of magnetic fields in magnetic memory devices. A range of compounds have now been found to exhibit intrinsic GMR—these are all perovskites based on manganese oxide1–4. Here we report the observation of GMR in Ti2Mn2O7, which has a pyrochlore structure and thus differs both structurally and electronically from perovskites. At 135 K the magnetoresistance ratio (the change in resistance) reaches–86% at 7 tesla, comparable to the GMR response of perovskite materials. In contrast to the hole-doped perovskites, the charge carriers in our material are electrons, as determined from measurements of the Hall coefficient. The discovery of GMR in a second class of material expands the options for optimizing magnetoresistive properties for specific technological applications.
309 citations
TL;DR: Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange.
Abstract: The effect of Fe doping (20%) on the Mn site in the ferromagnetic ($x=0.37$) and the antiferromagnetic ($x=0.53$) phases of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ has been studied. The same ionic radii of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Mn}}^{3+}$ cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange.
305 citations
01 Jan 1996
TL;DR: Ahn et al. as discussed by the authors studied the effect of Fe doping on the Mn site in the ferromagnetic and antiferromagnetic phases of (Formula presented) and found that conduction and ferromagnetism were consistently suppressed by Fe doping.
Abstract: Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.
273 citations
TL;DR: Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials.
Abstract: Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.94 to 2.00 angstroms) observed in phases based on LaMnO3 perovskites that exhibit CMR. Both results in Tl2Mn2O7 indicate oxidation states very close to Tl3+2Mn4+2O7. Thus, Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials. An alternate mechanism for CMR in Tl2Mn2O7 based on magnetic ordering driven by superexchange and strong spin-fluctuation scattering above the Curie temperature is proposed here.
256 citations
TL;DR: In this paper, it was proved by the systematic experimental investigations that the fieldinduced destruction of the charge-ordered state accompanying the lattice structural as well as metamagnetic transition is a major origin of such a colossal magnetoresistance (MR) behavior near the Curie temperature.
Abstract: Phenomena of colossal magnetoresistance (MR) or magnetic field induced insulator–metal (I–M) transitions have been investigated for single crystals of perovskite‐type manganese oxides with controlled carrier density and one‐electron bandwidth. In addition to the canonical MR behavior near the Curie temperature, the first‐order phase transition accompanying several orders of magnitude change in resistivity has been observed under an external magnetic field for many of the composition‐controlled crystals as an intrinsic bulk phenomenon. It was proved by the systematic experimental investigations that the field‐induced destruction of the charge‐ordered state accompanying the lattice structural as well as metamagnetic transition is a major origin of such a colossal MR. Versatile MR phenomena and I–M phase diagrams in the T–H plane are presented with their interpretation.
206 citations
TL;DR: In this paper, a single crystal of perovskite-type manganese oxide with finely controlled ionic radii of the A sites, (Nd,Sm) 1/2 Sr 1/1/2 MnO 3, was modeled as a first-order insulator-to-metal phase transition induced by a magnetic field.
Abstract: Magnetoresistance resulting in a drop in resistivity of more than three orders of magnitude that is strongly coupled to lattice striction has been observed under a relatively low magnetic field (0.4 tesla at 115 kelvin) for a single crystal of perovskite-type manganese oxide with finely controlled ionic radii of the A sites, (Nd,Sm) 1/2 Sr 1/2 MnO 3 . The colossal magnetoresistance phenomena are viewed as a first-order insulator-to-metal phase transition induced by a magnetic field, which accompanies a metamagnetic (antiferromagnetic-to-ferromagnetic) transition and a structural change in the lattice. Clear hystereses and abrupt changes in magnetization, striction, and resistivity were observed in increasing and decreasing magnetic fields at temperatures (113 to 150 kelvin) just above the Curie temperature.
122 citations
TL;DR: In this paper, Rao and Cheetham discuss magnetoresistance in perovskite manganates, where the effect is unusually strong and this understanding is driving the search for new materials with even more impressive properties.
Abstract: Some materials exhibit large changes in electrical resistance in the presence of a magnetic field, and this change can be used in applications from sensor technology to magnetic data storage. In their Perspective, Rao and Cheetham discuss magnetoresistance in perovskite manganates, where the effect is unusually strong. Much has been learned about these materials, and this understanding is driving the search for new materials with even more impressive properties.
115 citations
TL;DR: In this paper, it was found that La2−2xCa1+2xMn2O7 (x=0.25) is a metallic ferromagnet with a magnetic transition temperature Tc of 215 K.
Abstract: Bulk samples of La2−2xCa1+2xMn2O7 with the layered Sr3Ti2O7‐type perovskite structure have been successfully synthesized and investigated with respect to their magnetic and electrical properties. It is found that La2−2xCa1+2xMn2O7 (x=0.25) is a metallic ferromagnet with a magnetic transition temperature Tc of 215 K. The large magnetoresistance (MR) effect with Δρ/ρ0 of ∼60% at 1.8 T was observed in a wide temperature range below a cusp temperature in resistivity of 96 K, which is well below the magnetic Tc. This behavior is quite different from that of the well‐known double‐exchange ferromagnets such as La1−xCaxMnO3, where large MR effects are restricted to a narrow temperature range around the ferromagnetic transition. The present result could be interpreted by using the double‐exchange theory incorporating the anisotropy resulting from the two‐dimensional Mn‐O‐Mn networks in La2−2xCa1+2xMn2O7.
TL;DR: The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si and a close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures as mentioned in this paper.
Abstract: We are able to grow high quality La0.67Sr0.33MnO3(LSMO) colossal magnetoresistive (CMR) thin films on Y‐stabilized zirconia (YSZ) buffered (100) Si substrates using a Bi4Ti3O12 texturing and lattice matching layer. The CMR films have very high structural perfection and show excellent transport and ferromagnetic properties, including the almost full saturation magnetization values and narrow ferromagnetic resonance peaks (15 Oe at 290 K). The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si. A close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures.
TL;DR: In this paper, a thin La1−xCaxMnOδ with tetragonal symmetry was fabricated and the measured magnetoresistance is anisotropic: initially positive for applied magnetic field perpendicular to the film plane and negative for field applied parallel to the plane.
Abstract: We have fabricated thin films of La1−xCaxMnOδ with tetragonal symmetry. For low temperatures and magnetic fields the measured magnetoresistance is anisotropic: initially positive for applied magnetic field perpendicular to the film plane and negative for field applied parallel to the film plane. At high temperatures the magnetoresistance is negative for all fields and field orientations. We also observe an in‐plane magnetoresistance anisotropy with an angular dependence corresponding to that observed in transition metal ferromagnets. We suggest an interpretation requiring a substantial spin‐orbit interaction in the material.
Patent•
IBM1
TL;DR: In this article, a tri-layer thin film magnetoresistive device using doped perovskite manganate thin films as ferromagnetic elements, wherein a current is transported through the trilayer structure, is disclosed.
Abstract: A tri-layer thin film magnetoresistive device using doped perovskite manganate thin films as ferromagnetic elements, wherein a current is transported through the tri-layer structure, is disclosed. A large magnetoresistance change of about a factor of two is obtained in a low magnetic field, less than 150 Oe, which is close to the coercivity of the material of the elements. This device demonstrates that low-field spin-dependent transport in the manganates can be accomplished and that the magnitude of the resulting magnetoresistance is suitable for magnetoresistive field sensor applications.
TL;DR: The first high-pressure measurement of magnetoresistance in single crystal is performed, which rules out substrate-induced compressive strain as a source of enhanced magnetores resistance.
Abstract: To investigate the observed huge variations in magnetoresistance between different samples of manganite perovskites we have performed the first high-pressure measurement of magnetoresistance in single crystal Nd{sub 0.5}Sr{sub 0.36}Pb{sub 0.14}MnO{sub 3{minus}{delta}}. Both resistivity and magnetoresistance are strongly suppressed upon application of pressure. The decrease in magnetoresistance with increasing pressure rules out substrate-induced compressive strain as a source of enhanced magnetoresistance. Instead, the magnetoresistance differences between samples are ascribed primarily to the more abrupt nature of the semiconductorlike to metallic phase transition at lower temperatures. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this article, the low-frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 was measured in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state.
Abstract: We report measurements of the low‐frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state. We observe a bolometric optical response in fully oxygenated films of the above composition as well as in oxygen deficient films. In both types of samples, the optical response is thermal in nature as indicated by its proportionality with the temperature derivative of the resistance dR/dT.
TL;DR: In this paper, the specific heat of ferromagnetic metallic oxides was measured at 2.15 K and 3.3 K, respectively, and it was shown that the heat has terms proportional to {ital T} and {italT} and [ital T]sup 3/2}.
Abstract: We report measurements of the specific heat of La{sub 0.67}Ba{sub 0.33}MnO{sub 3} and La{sub 0.8}Ca{sub 0.2}MnO{sub 3} for temperatures 2{lt}{ital T}{lt}15 K. These materials are ferromagnetic metallic oxides which exhibit colossal magnetoresistance. We find that above 3 K the specific heat has terms proportional to {ital T} and {ital T}{sup 3}, but a {ital T}{sup 3/2} term, as might be expected from the excitation of ferromagnetic spin waves, cannot be resolved outside of the precision of the data. The cubic term gives Debye temperatures of 400{plus_minus}17 K, and the linear term gives electron densities of states which are enhanced over band-structure estimates. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this article, the successful sol-gel growth of colossal magnetoresistive La•Ca•Mn•O powder and epitaxial thin film was reported, and a transition from semiconductor (negative dρ/dT) to metal transition was observed at 225 K which was located in proximity to the magnetic transition temperature (Tc) of 228 K.
Abstract: The successful sol–gel growth of colossal magnetoresistive La‐Ca‐Mn‐O powder and epitaxial thin film is reported. Homogeneous powders were prepared at a temperature of 315 °C and epitaxial thin films were obtained on MgO(100) and LaAlO3(100) through heat treatment at 700–950 °C. A transition from semiconductor (negative dρ/dT) to metal (positive dρ/dT) was observed at 225 K, which was located in proximity to the magnetic transition temperature (Tc) of 228 K. A peak magnetoresistance ratio of ∼900% occurred at 220 K.
TL;DR: In this article, the effect of the interpolated cation size and the cation ratio on the transition temperature of the samarium manganites has been investigated, and the authors obtained a RR ratio of 10 5 at 75K under 5T for Sm 058 Sr 03 Ca 012 MnO 3 compound.
TL;DR: It is found that frequency mixing effects at very high magnetic fields cannot be explained by the Shoenberg magnetic interaction, but are instead probably caused by oscillations in the chemical potential which become important as the extreme quantum limit is approached.
Abstract: Magnetoresistance measurements carried out in pulsed magnetic fields of up to 60 T and at temperatures down to 350 mK and angle-dependent magnetoresistance experiments performed in quasistatic fields have been used to establish that the charge-transfer salt beta ''-(BEDT-TTF)(2)AuBr2 undergoes a change in electronic structure at similar to 10 T. We propose that this arises due to a field-induced transition between two different spin-density-wave states. Furthermore, at the highest magnetic fields, both the background magnetoresistance and effective masses of the quasiparticles were found to increase, possibly as a result of an enhancement of the density of states. It is found that frequency mixing effects at very high magnetic fields, observed in the Fourier spectra of the magnetoresistance, cannot be explained by the Shoenberg magnetic interaction, but are instead probably caused by oscillations in the chemical potential which become important as the extreme quantum limit is approached.
TL;DR: In view of the low conductivity and the absence of ferromagnetism, the CMR of these phases is not readily explained by a double-exchange mechanism as mentioned in this paper.
Abstract: Magnetization and magnetotransport measurements have been used to study the composition dependence of the electronic properties of the Ruddlesden - Popper phases and . Although their behaviour differs in detail, both compounds show a colossal magnetoresistance (CMR) effect (> 10000% in 14 T) in the temperature range . However, neither material shows a transition to a ferromagnetic state above 4.2 K, and both materials have higher resistivities ( for ) than the metallic oxides previously found to show CMR. In view of the low conductivity and the absence of ferromagnetism, the CMR of these phases is not readily explained by a double-exchange mechanism.
TL;DR: In this paper, it was shown empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H)=ρ∞+1/(σ 0+γ|H|) for T TC.
Abstract: The observed H2 and |H| dependence of the magnetoresistance above and below TC, respectively, may be explained by general time‐reversal symmetry considerations. We further find empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H)=ρ∞+1/(σ0+γ|H|) for T TC. This provides a functional form to analyze and predict the magnetoresistance over a wide range of fields. This suggests that the underlying mechanism of ‘‘colossal magnetoresistance ’’ may be magnetoconductive, not magnetoresistive. The magnetoresistance and Hall effects on an annealed epitaxial thin films of La0.67Ca0.33MnO3 were measured at 0.9 TC and 1.1 TC. At low fields, anisotropic magnetoresistance plays a dominant role. The high field Hall effect shows holelike carriers above and below TC. The apparent change in sign at low fields is likely due to the anomalous Hall effect.
TL;DR: In this paper, the magnetic field dependence of microwave absorption at low fields (200 Oe), in thin film and bulk samples of La1−xBaxMnO3−z.
Abstract: We report the magnetic field dependence of microwave absorption at low fields (200 Oe), in thin film and bulk samples of La1−xBaxMnO3−z. We demonstrate, using a very simple cavity configuration, that the magnetic field sensitivity of the microwave response of the giant magnetoresistance materials offers possibilities of using such materials in devices operating at low fields. Low‐field dc magnetization and ac resistivity measurements are also presented.
TL;DR: In this paper, the authors measured 1/f electrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3 and Pr 0.67Sr0.
Abstract: We report measurements of 1/f electrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3 and Pr0.67Sr0.33MnO3, which exhibit colossal magnetoresistance. The noise magnitude represented by the Hooge parameter is nearly 8 orders of magnitude larger than that observed in ordinary metals (and semiconductors) and nearly 5–6 orders of magnitude larger than that observed in epitaxial films of the perovskite oxide YBa2Cu3O7 in the normal state. The normalized noise spectral density increases with decreasing temperature below the resistivity peak, suggestive of the presence of additional low energy noise processes in the ferromagnetic metallic state.
TL;DR: In this article, it was proved by the systematic experimental investigations that the collapse of the charge-ordered state under a magnetic field, which accompanies the lattice-structural as well as metamagnetic transition, is a major origin of such a colossal magnetoresistance.
Abstract: Phenomena of colossal magnetoresistance (MR) or magnetic-field-induced insulator-metal (I-M) transitions have been investigated for single crystals of perovskite-type manganese oxides with controlled carrier density and one-electron bandwidth. In addition to the canonical MR behaviors near the Curie temperature, the first-order phase transition accompanying a several orders of magnitude change in resistivity has been observed under an external magnetic field for many of the composition-controlled crystals as an intrinsic bulk phenomenon. It was proved by the systematic experimental investigations that the collapse of the charge-ordered state under a magnetic field, which accompanies the lattice-structural as well as metamagnetic transition, is a major origin of such a colossal MR. Versatile MR phenomena and I-M phase diagrams in the T - H plane are presented with their interpretations.
TL;DR: In this article, the authors explored the colossal magnetoresistance (CMR) effect in the antiferromagnetic La0.5Ca 0.5MnO3 compound, where they observed a phenomenal one millionfold change in resistivity between 0 and 8 Tesla.
Abstract: We have explored the colossal magnetoresistance (CMR) effect in the antiferromagnetic La0.5Ca0.5MnO3 compound. In the absence of a magnetic field (H), the solid is a canted antiferromagnetic (AFM) insulator. An applied H in the Tesla scale induces a first order AFM to FM phase transition, and correspondingly, an insulator to metal transition. The observed CMR is attributed to the H‐induced charge localization‐delocalization behavior associated with the AFM–FM transition. At low temperatures (T<100 K), the solid remains in the AFM phase, where we have observed a phenomenal one millionfold change in resistivity between 0 and 8 Tesla. The origin of CMR in low T‐region is a thermal activation energy gap which is strongly dependent on H.
TL;DR: In this article, the authors examined the magnetic field and temperature-dependent resistivity and magnetization of a series of thin films that were grown via pulsed-laser deposition and found that the magnitude of the CMR effect in a given specimen is controlled not by ρ(Tc), but by Tc via the ratio ρ (Tc)/ρ(4 K).
Abstract: To determine the Tc dependence of the colossal magnetoresistance (CMR) exhibited by the ferromagnetic La07A03MnO3+δ (A=Ba, Ca, Sr) system, we examine the magnetic‐field and temperature‐dependent resistivity and magnetization of a series of thin films that were grown via pulsed‐laser deposition The films had magnetic ordering temperatures (Tc) ranging from 150 to 350 K All samples display a large negative MR that is largest near Tc, and samples with a low Tc display significantly larger MR values than do samples with large Tc’s The quantity ρ(Tc)/ρ(4 K), the amount by which the resistivity is reduced by full ferromagnetic order, varies as exp(Ea/Tc) with an activation energy Ea=01 eV These results indicate that the magnitude of the CMR effect in a given specimen is controlled not by ρ(Tc), but by Tc via the ratio ρ(Tc)/ρ(4 K) Phenomenological scaling relationships are also reported that link ρ(H,T) to both H and M(H,T)
TL;DR: In this paper, a spin-polaron Hamiltonian was proposed to study the electrical conductivity in perovskite structures, and it was found that most of the experimental observations on resistivity and magnetoresistance can be well explained with the assumption of the existence of spin clusters.
Abstract: A spin‐polaron Hamiltonian is proposed to study the electrical conductivity in perovskite structures. A crossover from the metallic conduction at low temperatures to the hopping‐type conduction at high temperature is calculated within the proposed model Hamiltonian. It is found that most of the experimental observations on resistivity and colossal magnetoresistance can be well explained with the assumption of the existence of spin clusters.
TL;DR: In this paper, thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011-1015 ions/cm2) of 200 keV Ar+ ions.
Abstract: Thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011–1015 ions/cm2) of 200 keV Ar+ ions. The implanted samples were examined by ion channeling and x‐ray diffraction techniques. The channeling results clearly showed that the magnitude of the induced lattice disorder did not increase greatly for implantation doses up to 5×1013 ions/cm2. In this low dose implantation regime, the magnetoresistance {MR=[R(0)−R(H)]/R(0)} increased by 50%, the peak resistivity went up by two orders of magnitude, and the magnetoresistivity peak temperature decreased by 130 K compared to the original, unimplanted sample. For doses ≥5×1013 ions/cm2, the damage was significant and caused the sample to become semiconducting.
TL;DR: In this article, a comparison of manganite perovskites La0.7−xYxCa0.3 and manganites Pr 0.7Ca 0.3 was made and it was shown that the Mn(III)-Mn(IV) mixed valence (hole carrier density) and the size of the interpolated cations are the two main factors that govern the transition temperature T1.
Abstract: Colossal magnetoresistance (CMR) properties have been evidenced for the manganese perovskites La0.7−xYxCa0.3MnO3−δ with 0.01≤x≤0.20. This system is compared to the manganites Pr0.7Ca0.3−xSrxMnO3−δ that exhibit the same Mn(III)/Mn(IV) ratio. Like for this second system, one observes that the transition temperature T1 increases as the size of the interpolated cation increases from 75 to 225 K. This comparison demonstrates that the Mn(III)–Mn(IV) mixed valence (hole carrier density) and the size of the interpolated cations are the two main factors that govern the transition temperature T1. However, the CMR effect characterized by the resistance ratio (RR) R0/RB (R0 resistance in zero magnetic field and RB resistance in a magnetic field, B=5 T) is much lower than that observed for the Pr manganites. The highest RR value is of 40 for La–Y phases for T=120 K (x=0.10) against 2.5×105 for the Pr phase for T=88 K (x=0.05). Thus, it is suggested that the electronic configuration of the interpolated cation may play ...