Magnetic Transitions and Magneto-Transport in Epitaxial Pr 0.5 Sr 0.5 MnO 3 Thin Films (original) (raw)
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We have synthesized and investigated the effect of Ag doping in Pr 0.67 Sr 1 À x Ag x MnO 3 (0 r x r0.3) perovskite materials via solid state reaction route. The structural, transport and magnetoresistance behavior have been studied. The Rietveld refinement of X-ray diffraction data shows that the compounds crystallize in an orthorhombic structure with Pnma space group with systematic non-linear variation in unit cell volume and lattice parameters. The grain morphology confirms that silver enhances conducting channels and reacts well with the compound only upto a certain doping level. The temperature dependent zero-field and in-field resistivity have been measured between 5 K and 300 K. The samples exhibit a systematic variation in metal to insulator transition temperature and a large magnetoresistance at x ¼ 0.10. The highest value of temperature coefficient of resistance has been observed by us for the first time. The results revealed that Ag takes part in the reaction only when the doping amount is small and at higher doping the system becomes a two phase composite.
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.
Effect of Quenching on Magnetoresistance Properties in the Pr0.5Sr0.5MnO3 Perovskite Manganite
Journal of Solid State Chemistry, 2002
We report on the magnetization, resistivity and magnetoresistance (MR) measurements on polycrystalline Pr 0.5 Sr 0.5 MnO 3. Quenching samples from 14003C to room temperature in water (sample I) or in air (sample II) leads to di4erent behaviors. Powder X-ray di4raction patterns for samples I and II could be indexed, respectively, in rhombohedral perovskite structure with R3 c space group and in the orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic+ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sample I presents a ferromagnetic spin-canted state, while sample II behaves as an antiferromagnet below 160 K. Resistivity and magnetoresistance studies show a net di4erence as a function of the quenching conditions.
Nonmagnetic Sc Substitution in a Perovskite Ferromagnetic Insulator Pr 0.8 Ca 0.2 MnO 3
Journal of the Physical Society of Japan, 2013
The effect of nonmagnetic substitution in a perovskite ferromagnetic insulator Pr 0:8 Ca 0:2 MnO 3 was studied in epitaxial Pr 0:8 Ca 0:2 Mn 1Ày Sc y O 3 thin films grown on SrTiO 3 substrates. An increasing Sc substitution level weakened the ferromagnetic order, resulting in a decrease of saturation magnetization and the ferromagnetic transition temperature. Analysis of transport properties and Raman spectra indicates that besides simple spin dilution, weakening of both the double-exchange interaction and orbital order contributes to the reduction of ferromagnetic order.
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
Structure and magnetism in the Pr1−xNaxMnO3 perovskites (0 ⩽ x ⩽ 0.2)
Journal of Magnetism and Magnetic Materials, 2002
The mixed-valence manganites Pr 1Àx Na x MnO 3 have been investigated by neutron diffraction, electric transport and magnetic measurements. Similarly to related systems with divalent alkali earths, the increasing monovalent sodium substitution decreases the Jahn-Teller deformation of the MnO 6 octahedra, lowers the resistivity and changes gradually the magnetic ordering from the layered type antiferromagnetism (x ¼ 0) through spin-canted arrangements (xB0:05) to the pure ferromagnetism (0:10pxp0:15) with T C B125 K. The samples with ferromagnetic ground state are not metallic below T C but show appreciable magnetoresistive effects in a broad temperature region. The electronic localization at low temperatures is further enhanced in the sample with the maximum sodium content xB0:2: Electron and neutron diffraction evidences that Pr 0.8 Na 0.2 MnO 3 exhibits a commensurate charge and orbital ordering of the Mn 3+ /Mn 4+ (1:1) kind below T co ¼ 215 K, followed with a transition to the antiferromagnetic arrangement of pseudo-CE type at T N ¼ 175 K, analogous to that of previously studied Pr 0.65 Ca 0.35 MnO 3 . In addition, Pr 0.8 Na 0.2 MnO 3 undergoes below B50 K a spin reorientation and, simultaneously, ferromagnetic clusters in the charge-ordered matrix are formed. By application of external field of 2-5 T below T co ; the insulating charge-ordered antiferromagnet is transformed to a metallic ferromagnetic state which is persistent below B60 K, i.e. temperature close to the spin reorientation transition. r
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.
Neutron diffraction, NMR and magneto-transport properties in the Pr0.6Sr0.4MnO3 perovskite manganite
Journal of Alloys and Compounds, 2002
A Pr Sr MnO powder was synthesized by the solid state reaction method at 14008C. Magnetic measurements show that our sample 0.6 0.4 3 exhibits a paramagnetic-ferromagnetic transition with decreasing temperature. The paramagnetic to ferromagnetic transition is followed by a decrease of the magnetization below 100 K. The Curie temperature T is found to be 310 K. Electrical studies show a C semiconductor-metallic transition at T 5 260 K. Our sample displays a magnetoresistance effect in 8 T of about 45% below 250 K. r Neutron diffraction studies show that our sample crystallizes in the orthorhrombic system with Pnma space group at room temperature and at 200 K. However, at 10 K, we observe the coexistence of two phases: an orthorhombic phase with Pnma space group (27%) and a 55 monoclinic one with 12 /a space group (73%). Mn NMR measurements at 4.2 confirm the metallic behavior at low temperature. The 41 31 observed frequency of 380 MHz is close to the calculated frequency of 378 MHz, which confirms the average value of Mn and Mn resonance frequencies.
Journal of Applied Physics, 1997
The effects of lattice distortion on the physical properties of La 0.7 Ca 0.3 MnO 3 epitaxial films are investigated. Our results suggest that larger substrate-induced lattice distortion gives rise to larger zero-field resistivity and larger negative magnetoresistance. Similar effects are also observed in samples of different thicknesses and on the same substrate material, with larger resistivity and magnetoresistance associated with thinner samples. In addition to x-ray diffraction spectroscopy, the degrees of lattice distortion in different samples are further verified by the surface topography taken with a low-temperature scanning tunneling microscope. Quantitative analyses of the transport properties suggest that the high-temperature (T→T C) colossal magnetoresistance ͑CMR͒ in the manganites is consistent with the conduction of lattice polarons induced by the Jahn-Teller coupling, and that the low-temperature (TӶT C) magnetoresistance may be attributed to the magnetic domain wall scattering. In contrast, the absence of the Jahn-Teller coupling and the large conductivity in La 0.5 Ca 0.5 CoO 3 epitaxial films yield much smaller negative magnetoresistance, which may be attributed to disorder-spin scattering.
First-order antiferromagnetic and structural transition in Sr-rich Pr[sub 1−x]Sr[sub x]MnO[sub 3]
Journal of Applied Physics, 2001
We present magnetization and resistivity data on polycrystalline samples of Pr 1Ϫx Sr x MnO 3 (0.58 рxр1.00). All the samples are antiferromagnetic insulators at low temperatures. For 0.78Ͻx Ͻ0.90, and for xϭ0.58, both resistivity and magnetization show a clear hysteresis which indicates the first-order nature of the antiferromagnetic transition. Neutron diffraction data show that the paramagnetic-to-antiferromagnetic transition is accompanied by a cubic-to-tetragonal structural transition for 0.78ϽxϽ0.90, and tetragonal-to-orthorombic transition for xϭ0.58. The other samples exhibit continuous transitions to the antiferromagnetic state. Our results show that the structural transitions are the origin of the discontinuous magnetic and resistive transitions. A moderate magnetoresistance effect can be observed for a lower Sr content possibly due to ferromagnetic fluctuations.