Nonmagnetic Sc Substitution in a Perovskite Ferromagnetic Insulator Pr 0.8 Ca 0.2 MnO 3 (original) (raw)
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Magnetic Transitions and Magneto-Transport in Epitaxial Pr 0.5 Sr 0.5 MnO 3 Thin Films
Le Journal de Physique IV, 1996
Epitaxial thin films of the tnagnetic perovskite Pro.5Sr0.5M~~03 were prepared by dcmagnetron sputtering, structurally cha.racterized by x-ray diffraction and their physical properties investigated by magnetization and electrical transport nieasurements. Ferromagnetic ordering appears in zero-field at 263 K, followed by a second transitioii into an antiferromagnetic state at 160 K. The zero-field resistivity has a semiconducting behaviour according to Mott's law and becomes quasi-metallic only within the ferrorilagnetic st,ate, whose temperature range can be extended by applying an external niagnetic field. The negative rnagslet.oresist,aslce effect increases systematically with decreasing t.eniperature and reaches a value of 700 % at 1.5 K in a field of 12 T. For lemperatures below 75 K we observed additionally a memory effect, showing up as a persistent, field induced loweri~lg of sample resistivity.
Effect of Ce doping on structural, magnetic, and transport properties of SrMnO 3 perovskite
We have systematically investigated the structural, magnetic, and transport properties of the Sr 1−x Ce x MnO 3 0 x 0.35 system as a function of temperature and magnetic field. For x 0.10, the system does not show any long-range magnetic ordering but spin-glass-like behavior at low temperatures below T SG. The in-phase susceptibility below T SG decreases and T SG shifts toward higher temperature with the frequency of an ac magnetic field. In the paramagnetic state, exhibits an unusual T dependence due to the formation of a microscopic inhomogeneous magnetic phase. For the x = 0.25 sample, both and show an anomaly at around 110 K due to a charge-ordering transition. Both the x = 0.25 and 0.35 samples show large negative magnetore-sistance over a wide range of T.
Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite
Pramana, 2002
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO 3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La 1−2x Pr x Ca x )MnO 3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x = 0.1, 0.15, 0.2), the T c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.
Metal–insulator transition and magnetotransport in III–V compound diluted magnetic semiconductors
Materials Science and Engineering: B, 1999
We investigated the nature of transport and magnetic properties in SrIr 0.5 Ru 0.5 O 3 , (SIRO) which has characteristics intermediate between a correlated non-Fermi liquid state and an itinerant Fermi liquid state, by growing perovskite thin films on various substrates (e.g. SrTiO 3 (001), (LaAlO 3) 0.3 (Sr 2 TaAlO 6) 0.7 (001) and LaAlO 3 (001)). We observed systematic variation of underlying substrate dependent metal-to-insulator transition temperatures (T MIT ∼80 K on SrTiO 3 , ∼90 K on (LaAlO 3) 0.3 (Sr 2 TaAlO 6) 0.7 and ∼100 K on LaAlO 3) in resistivity. At temperature 300 K ≥ T ≥ T MIT , SIRO is metallic and its resistivity follows a T 3/2 power law; whereas insulating nature at T < T MIT is due to the localization effect. Magnetoresistance (MR) measurement of SIRO on SrTiO 3 (001) shows negative MR at T < 25 K and positive MR at T > 25 K, with negative MR ∝ √B and positive MR ∝ B 2 ; consistent with the localized-to-normal transport crossover dynamics. Furthermore, observed spin glass like behavior of SIRO on SrTiO 3 (001) at T < 25 K in the localized regime, validates the hypothesis that (Anderson) localization favors glassy ordering. These remarkable features provide a promising approach for future applications and of fundamental interest in oxide thin films.
Materials Research Express, 2014
Magnetic and magnetotransport properties of oriented polycrystalline Pr 0.58 Ca 0.42 MnO 3 thin films prepared in flowing oxygen and air ambient has been investigated. The magnetic ground state of both the films is a frozen cluster glass. In the air annealed film charge order (CO) is quenched and ferromagnetic (FM) transition, which appears at T C 148 K is followed by antiferromagnetic (AFM) transition at T N 104 K. This film shows self-field hysteretic insulator-metal transition (IMT) at T IM C 89 K and T IM W 148 K in the cooling and warming cycle, respectively. Application of magnetic field (H) gradually enhances T IM C and T IM W , reduces the thermoresistive hysteresis and T IM (=T IM W -T IM C ) diminishes. In contrast, the
Journal of Solid State Chemistry, 2005
Magnetic and electronic properties of the oxygen deficient ordered perovskite, Sr 2/3 Y 1/3 CoO 8/3+d , have been studied for two different oxygen contents corresponding to d ¼ 0:00 and 0:04 in the chemical formula. For the former, at low temperature, the background state is antiferromagnetic insulating ðT N ¼ 290 K; r 10 K ¼ 4 Â 10 5 O cmÞ as expected from the presence of trivalent cobalt in the high spin-state. Remarkably, the more oxidized compound with a cobalt oxidation state of E3.08 is a ferromagnetic half-metal with T C ¼ 225 K and r 10 K ¼ 2 Â 10 À3 O cm: Consistently, upon application of an external magnetic field, the spinscattering reduction in the T C vicinity is responsible for a weak negative magnetoresistance. These dramatic changes of the physical properties for such a slight increase of the cobalt oxidation state are interpreted as a result of the structural disordering created by the extra oxygens. The thermoelectric power measurements, showing a sign change of the Seebeck coefficient as the oxygen content increases, indicate that electrons moving in a metallic e g band dominate the transport properties of the ferromagnetic and metallic compound. This suggests the existence of an orbital ordering in the pristine compound, related to an ordered array of CoO 4 tetrahedra, which can be collapsed by the presence of these extra oxygen anions. r
Metal-insulator transition of ferromagnetic ordered double perovskites: (Sr1−yCay)2FeReO6
Physical Review B, 2002
Temperature-and composition-control metal-insulator ͑M-I͒ transitions have been investigated for ordered double perovskites, (Sr 1Ϫy Ca y) 2 FeReO 6. Ca 2 FeReO 6 (yϭ1) shows the thermally induced M-I transition associated with the lattice-structural transition around 150 K. The alloyed system undergoes the M-I transition in the almost fully spin-polarized ground state around yϭ0.4 with minimal enhancement of the electronic specific-heat coefficient but with a large energy-scale (ϳ1 eV) change of the optical conductivity spectrum. These results indicate the importance of electron correlation, in particular the orbital correlation of Re t 2g electrons, for the ferromagnetic M-I transition.
Magneto-transport studies on (Pr 1/3 Sm 2/3 ) 2/3 A 1/3 MnO 3 (A = Ca, Sr and Ba) compounds
Journal of Physics: Condensed Matter, 2004
Magnetic and transport properties of (Pr 1/3 Sm 2/3 ) 2/3 A 1/3 MnO 3 (A = Ca, Sr and Ba) compounds, prepared by the citrate gel route, have been investigated. These compounds are found to crystallize in the orthorhombic structure. Charge ordering transport behavior is indicated only in Ca-substituted compound. The Sr-and Ba-substituted compounds show metal-insulator transition and semiconducting-like behavior, respectively. The magnetoresistance is highest in the Ba substituted compound. All the three samples show irreversibility in magnetization as a function of temperature in zero-field cooled (ZFC) and field cooled (FC) plots. The non-saturating magnetization, even at 5K and 4 Tesla field, are observed in Ca as well Ba-substituted compounds. data storage by increasing the sensitivity of hard disk drive read heads [1,2]. These manganites become ferromagnetic (FM) at an optimal value of x (or Mn 4+ content) and undergo metal-insulator (MI) transition around the ferromagnetic transition temperature. Effects of divalent alkaline-earth element substitution in the stoichiometric perovskite manganites Ln 1-x A x Mn 1-y M y O 3 have been extensively studied [3,5]. These studies show that the Curie temperature, T C , and the magnetoresistance are optimized for Mn 4+ content of about 33%. These properties are attributed to the double exchange (DE) interaction associated with electron hopping from Mn 3+ to Mn 4+ . The double exchange interaction, which favors itinerant electron behaviour, is opposed by the Jahn-Teller (JT) distortion of 1 the Mn 3+ . Recent studies have shown that DE alone cannot explain the observed behavior in manganites [6] and other effects also play an important role. These include charge ordering, average A-site cationic radius [7,8], A-size cationic size mismatch [9,10], oxygen deficiency [11], electron-lattice coupling [12], polaron effect due to strong electron-phonon interaction arising from the Jahn-Teller distortion [6], etc. The average size of the A-site cation of these perovskites and the size mismatch at the A-site modify the Mn-O-Mn bond angle and affect the e g electron hopping between Mn 3+ and Mn 4+ degenerate states. The effect of ionic size variation can also be understood by the tolerance factor defined as, t = ( + r O )/√2 (r B +r O ), where r O and r B are radii of the oxygen and the B-site transition metal ions, respectively. The electronic properties of the manganites can be tuned either by substituting cations at the A-or B-sites or by varying the oxygen content in the regular perovskites structure [13-15]. The A-site cation is responsible for structural distortions while the Bsite cation is responsible for the magnetic interactions. Mixing cations of different charges at the A-site is the most straightforward experimental method for systematically tuning the properties of these materials. There are many ways to achieve this with Ln 3+ /M 2+ combinations (Ln = rare earth and M = Ca, Ba Sr and Pb) or with rare earth ion combinations. This has led to efforts to unify the properties of compositions from different chemical phase diagrams within a single framework by using a simple ionic description of the A-site cations [16].
Atomic replacement effects on the band structure of doped perovskite thin films
Scientific Reports, 2019
The potential applications of perovskite manganite R 1-x A x Mno 3 (R = rare earth element; A = Sr, Ca) thin films have been continuously explored due to their multi-functional properties. In particular, the optimally hole-doped La 0.67 Ca 0.33 Mno 3 thin film demonstrates a colossal magneto-resistance that is beneficial to the performance of spintronic devices. To understand the effect of R and A ions on the material properties, we systematically measure the resistivity, magnetization, and electronic energy states for three optimally hole-doped R 0.67 A 0.33 Mno 3 thin films with R = La, Sm and A = Sr, Ca. Various energy parameters are derived based on the X-ray absorption and X-ray photoelectron spectra, including the band gap, the charge frustration energy and the magnetic exchange energy. It is interesting to find that the replacement of La with Sm is more effective than that of Sr with Ca in terms of tuning the electrical property, the Curie temperature, and the band gap. The strain-induced reduction of the O 2p-Mn 3d hybridization and the interplay of R/A site disorder and strain effect are discussed. The results of this study provide useful information for the band design of perovskite oxide films. Perovskite manganite R 1-x A x MnO 3 (R = rare earth element; A = alkaline metal) has attracted long standing attention because of its fascinating properties related to the correlations between spin, charge, and orbital degrees of freedom. In 1994, the discovery of colossal magneto-resistance in ferromagnetic La 0.67 Ca 0.33 MnO 3 thin films activated the potential applications of perovskite oxides on magnetic recording media 1. However, there are still many issues to resolve before the practical integration of perovskite oxides into semiconductor devices. They include developing an understanding of the band structure and controlling the band gap. Similar to conventional semiconductors, the electronic structure of R 1-x A x MnO 3 can be tuned using either hole doping (x > 0) 2-8 or internal strain 7,8. Unlike conventional semiconductors, the transport mechanism of R 1-x A x MnO 3 involves strong electron-electron correlations, leading to complex transport properties different from the typical metallic or insulating behavior. Strong on-site repulsion (Hubbard U-term) between 3d electrons may cause an integer-filled 3d n configuration, resulting in a Mott-insulator. Before turning into a Mott-insulator, the degree of hybridization of O-2p and Mn-3d bands may be modified to cover a wide range of transport properties from the charge-transfer type (such as AMnO 3) to Mott-Hubbard type (such as in RMnO 3) 9-12. Based on the Mott-Hubbard type theory, the charge fluctuations of between d n (i)d n (j) and d n-1 (i)d n+1 (j) states are strongly suppressed by high exchange energies, with i and j being different transition-metal sites. Additionally, the unique characteristics of the intermedium state open a new channel to tune the gap energy via ionic valence. Many reports suggest that the magnetic and electrical properties of mixed-valence R 1-x A x MnO 3 compounds could be modified either by changing the doping level, x, or by inserting various rare earth elements 13-17. Accordingly, a reduction of the effective ionic size r eff [r eff = (1 − x)r Rare + xr Alkai ] would enhance the local deformation of MnO 6 octahedron and narrow the effective width of the e g band. An increment of the ionic radii mismatch between R and A could also induce quenched lattice disorder 16 , which influences the stability of the ferromagnetic/orbital phase. Here, the x-effect is more complex since the variation of x could simultaneously change both the carrier concentration and the effective ionic size. Therefore, a simple approach to study the pure ionic effect is to fix the doping concentration. To design a functional read-write device, the required energies of switching between different electronic states are crucial. Overall, the correlation between crystal structure, electronic energy state, the electrical transport and magnetic property in manganite oxides is not yet fully understood 14-17 .
Physical Review B, 2001
Electric-and magnetic-field-dependent resistivity, and magnetization are studied in epitaxial films of Pr 0.7 Ca 0.3Ϫx Sr x MnO 3 between 4.2 and 300 K. Attention is focused on how the substitution of Sr at the Ca sites of the parent compound Pr 0.7 Ca 0.3 MnO 3 affects the electrical and magnetic states of this canonical chargeordered ͑CO͒ insulator. The resistivity ͑͒ of the parent compound is characterized by a gradual increase on cooling below 300 until 205 K, where it shows a steplike enhancement. We identify this step as the onset temperature (T CO) of the CO state. Below 205 K, a well-defined Arrhenius-type of resistivity with activation energy of 0.13 eV suggests excitation of holes across the CO gap as the mechanism of charge transport in the parent compound. In the films with xϭ0.03 and 0.07, this band-to-band excitation process gives way to a Mott-type, spin-dependent hopping transport from T CO to a crossover temperature T 2 (ϽT CO). Over a narrow temperature range below T 2 and a second crossover temperature T 3 , the films show a metallic character followed by the onset of a second insulating state, which persists down to the lowest temperature of measurement ͑4.2 K͒. In the regime of temperature between T 2 and 4.2 K, the transport in films with xϭ0.03 and 0.07 is highly nonlinear in electric field, and displays hysteretic and history effects. In this regime of temperature, the resistivity also shows a large drop on application of a magnetic field. In samples with xу0.1, while the large magnetoresistance in the vicinity of T 2 and the minimum in at T 3 persist, the transport remains Ohmic. Our magnetization measurements show the onset of ferromagnetic ordering in the vicinity of T 2 in all Srsubstituted films. However, for xϽ0.1, a low value of the field-cooled moment and a spin-glass type of behavior seen at temperatures below T 3 suggest formation of ferromagnetic clusters whose moment is gradually blocked with decreasing temperature. We argue that the nonlinear and hysteretic effects seen in samples with xр0.1 are a result of classical percolation and quantum transport in a topologically inhomogeneous medium.