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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Thickness dependence of the magnetic anisotropy in La2/3Ca1/3MnO3 thin films grown on LaAlO3 substrates

S. Valencia, Ll. Balcells, B. Martínez, and J. Fontcuberta

J. Appl. Phys. 93, 8059 (2003); http://dx.doi.org/10.1063/1.1556936 (3 pages) | Cited 17 times

Online Publication Date: 9 May 2003

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Magnetic anisotropy of sputtered epitaxial La2/3Ca1/3MnO3 (LCMO) thin films grown on top of LaAlO3 (LAO) substrates has been studied as a function of thickness. A series of films with thickness ranging from 20 to 150 nm have been prepared. LCMO films grown on LAO substrates are subjected to an in-plane biaxial compressive strain that progressively relaxes as film thickness increases as deduced from the variation of the c cell parameter. Nevertheless, some strain is observed even in 150-nm-thick films. The relaxation process is accompanied by an improvement of the magnetic and transport properties approaching that of the bulk material. The observed magnetic easy axis evolves from perpendicular to plane for thin films towards in plane as film thickness increases. Values of the effective anisotropy constant of K1eff≈2.2×107 erg/cm3, at T=10 K, and magnetostriction constant of λ≈2×10−4 are found. © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
68.60.Bs Mechanical and acoustical properties
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Low-frequency noise in patterned La0.7Sr0.3MnO3 thin films

L. Méchin, F. Yang, J.-M. Routoure, and D. Robbes

J. Appl. Phys. 93, 8062 (2003); http://dx.doi.org/10.1063/1.1556937 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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The low frequency noise in patterned La0.7Sr0.3MnO3 thin film bridges with different geometries was measured at 300 K in ambient magnetic field. Films were deposited by pulsed laser ablation on (100) SrTiO3 substrates. The measured 1/f noise was well described by the semiempirical Hooge relation, which indicates that the low frequency noise could be originated by resistance fluctuations. The measured noise magnitude was compared with bibliographic data for epitaxial La1−xSrxMnO3 (LSMO) and La1−xCaxMnO3 thin films. The normalized Hooge parameter α/n for our films was in the range of 2–4×10−28 m3, which is the order of magnitude of the best results reported in literature for oxygen annealed films. Finally the noise equivalent temperature of a thermometer fabricated with such LSMO films was estimated to be 3.4×10−6 K/math at 300 K, 10 Hz, and I=100 μA. These results demonstrate that the intrinsic low frequency noise of LSMO is not a limitation and that LSMO thin films can advantageously be used as performant thermometers for the fabrication of room temperature microbolometers. © 2003 American Institute of Physics.
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73.50.Td Noise processes and phenomena
73.61.Ng Insulators
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
07.20.Dt Thermometers
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Charge localization in nanometric La2/3Ca1/3MnO3 thin films grown on nearly matching substrates

G. Herranz, M. Berkowski, E. Jedryka, M. Wojcik, F. Sánchez, M. Bibes, and J. Fontcuberta

J. Appl. Phys. 93, 8065 (2003); http://dx.doi.org/10.1063/1.1556938 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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By using magnetotransport measurements as well as nuclear magnetic resonance as local magnetic probe, we conclusively show that, irrespective of the film/substrate structural mismatch and film thickness, there are nonconductive regions at the film/substrate interface. We thus discard dimensional effects and structural mismatch as the main reasons for the suppression of conductivity and the weakening of the ferromagnetic coupling in nanometric thin films of manganites. We shall argue that this behavior is related to a charge localization which also leads to a weakening of the magnetic interactions and a decrease of the Curie temperature. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Ferromagnetic resonance and electric characterization in double perovskite Sr2FeMoO6

A. G. Flores, M. Zazo, V. Raposo, J. Íñiguez, C. de Francisco, and P. Hernández-Gómez

J. Appl. Phys. 93, 8068 (2003); http://dx.doi.org/10.1063/1.1540180 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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In this work the study of the ferromagnetic resonance (FMR) and of the electrical conductivity in the perovskite sample, Sr2FeMoO6, is presented. The sample has been manufactured by conventional ceramic method sintering in inert gas atmosphere. Electrical conductivity, of about 1000–1200 S/m, has been measured in the 125–300 K temperature range. FMR linewidths have been measured at 9.48 GHz from 125 to 300 K. A decrease of the linewidth with increasing temperature has been obtained. This behavior has been attributed to the presence of valence exchange mechanism, which takes places in samples with Fe2+ cations. In this way, FMR linewidth analysis has been revealed like a useful and clear technique in determining the cation distribution of the sample showing the presence of Fe2+ ions. This technique has also shown data about the microstructure of the sintered polycrystalline sample finding the porosity value of the sample. © 2003 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Dd Nonmetallic ferromagnetic materials
72.20.Fr Low-field transport and mobility; piezoresistance
75.30.Et Exchange and superexchange interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Combustion synthesis of the magnetoresistive double perovskite (Ba1.6Sr0.4)FeMoO6

A. P. Douvalis, M. Venkatesan, P. Velasco, C. B. Fitzgerald, and J. M. D. Coey

J. Appl. Phys. 93, 8071 (2003); http://dx.doi.org/10.1063/1.1544452 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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Structural, magnetic, and magnetoresistive properties of the double perovskite (Ba1.6Sr0.4)FeMoO6, produced by two different methods are compared. The low field magnetoresistance effect at room temperature reaches a value of 10% in a field of 425 mT in samples prepared by combustion synthesis, whereas a field of 1110 mT is required for the same magnetoresistance in samples prepared by solid state reaction. The proportion of Fe/Mo antisite defects, determined by Mössbauer spectroscopy, is twice as great for the former as for the latter, and influences both the magnetic and magnetoresistive properties. The valence state of iron ions in different cation neighbor environments in (Ba1.6Sr0.4)FeMoO6, evaluated from the Mössbauer hyperfine parameters, is consistent with that found for a series of other isostructural iron-based double perovskites. © 2003 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.66.Fn Inorganic compounds
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.50.Dd Nonmetallic ferromagnetic materials

Phase coexistence in Cr-doped Nd0.5Ca0.5MnO3 compounds

A. S. Carneiro, F. C. Fonseca, R. F. Jardim, and T. Kimura

J. Appl. Phys. 93, 8074 (2003); http://dx.doi.org/10.1063/1.1540181 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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We have performed measurements of dc electrical resistivity ρ(T), magnetic susceptibility χ(T), and impedance spectroscopy Z(T, ω) in both single crystals and polycrystalline samples of Nd0.5Ca0.5Mn1−xCrxO3 (0.00⩽x⩽0.07). The pristine compound exhibits a transition to a charge ordered (CO) state at TCO∼250 K. However, no evidence of either metal-insulator (MI) or ferromagnetic (FM) transitions are observed at lower temperatures. The substitution of Mn by Cr partially suppresses the CO transition and induces a FM/MI ordering at lower temperatures TC=TMI∼140 K, which is essentially Cr independent. Both ρ(T) and χ(T) measurements indicate the development of a ferromagnetic (FM) component at low temperatures T<TMI that gradually increases with increasing Cr content. The ρ(T) and χ(T) data also revealed irreversibility at temperatures T<TCO suggesting a coexistence of different phases. In addition, the Z(T,ω) curves close to TMI exhibit a clear relaxation process. The specific capacitances calculated from the Z(T,ω) curves have a percolation-like behavior, characteristic of a metal-insulator transition in samples comprised of two phases. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics

Model of ground state in electron-doped Ca1−xSmxMnO3 (0<x⩽0.20) manganites and ferromagnetic resonance probing of “spontaneous ferromagnetism” in Ca0.8Sm0.2MnO3

M. Auslender, A. I. Shames, E. Rozenberg, G. Gorodetsky, C. Martin, and A. Maignan

J. Appl. Phys. 93, 8077 (2003); http://dx.doi.org/10.1063/1.1558692 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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The model of magnetoimpurity states in an antiferromagnet (AF) by De Gennes is suggested to explain magnetic properties and mixed ground state in the electron-doped manganites Ca1−xSmxMnO3 (0<x⩽0.2). The model predicts that an AF phase of Ca1−xSmxMnO3 is a nonhomogeneous one with strong spatial fluctuations of the magnetic order parameters at a given temperature. The experimental electron paramagnetic and ferromagnetic resonance study performed for the x=0.2 compound reasonably accords with this model. In particular, two new temperature scales revealed in the experiment are naturally explained. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Hx Magnetic impurity interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Oxygen vacancies effect on phase separation in Pr0.5Ca0.2Sr0.3MnO3−δ

D. Niebieskikwiat, A. Caneiro, and R. D. Sánchez

J. Appl. Phys. 93, 8080 (2003); http://dx.doi.org/10.1063/1.1540182 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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We study the effect of the introduction of a controlled amount of oxygen vacancies on the magnetic and transport properties of the phase separated manganite Pr0.5Ca0.2Sr0.3MnO3−δ, for δ=0 and 0.01. This compound presents a paramagnetic to ferromagnetic (FM) transition below TC∼240 K, and then to a charge-ordered (CO) and antiferromagnetic (AFM) phase at TCO∼175 K. However, below TCO an appreciable FM component (∼20%) still survives, related to a FM volume immersed within the CO/AFM matrix. At low temperatures, in the mainly CO phase, the introduction of oxygen vacancies enhances the FM ordering, with the consequent decrease of resistivity and magnetoresistance (MR). On the contrary, in the FM phase (in the range TCO<T<TC) the magnetization is reduced and the resistivity and MR increase. These results are discussed in the frame of percolative transport in metal–insulator mixtures, and frustrated double exchange interaction due to the interruption of some Mn–O–Mn chains. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
61.72.J- Point defects and defect clusters
75.47.Lx Magnetic oxides
75.30.Et Exchange and superexchange interactions
75.47.Gk Colossal magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions

Magnetoresistive behavior of Cr-doped manganites Pr0.44Sr0.56MnO3

Z. Jirák, J. Hejtmánek, K. Knížek, M. Maryško, C. Martin, A. Maignan, and M. Hervieu

J. Appl. Phys. 93, 8083 (2003); http://dx.doi.org/10.1063/1.1556939 (3 pages)

Online Publication Date: 9 May 2003

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A complex structural, magnetic, and electric transport investigation shows that the Cr doping on Mn sites in the A-type antiferromagnet Pr0.44Sr0.56MnO3 provokes a nonuniform magnetic state with coexisting ferromagnetic and antiferromagnetic regions. Irrespective of the ratio of magnetic phases, the samples exhibit a nonmetallic behavior of resistivity and thermopower, pointing to the nanoscopic nature of the phase separation. A particularly large magnetoresistance encountered in a broad range of temperatures for samples with Cr doping of 4%–6% supports such an idea. © 2003 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Lx Magnetic oxides
72.20.Pa Thermoelectric and thermomagnetic effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
64.75.-g Phase equilibria
61.46.-w Structure of nanoscale materials
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators

Giant magnetoresistance properties of the La1−2xRxAxMnO3 (R=Nd, A=Ca) perovskites

Darshan C. Kundaliya, A. A. Tulapurkar, S. R. Shinde, R. Pinto, W. B. Yelon, R. G. Kulkarni, and S. K. Malik

J. Appl. Phys. 93, 8086 (2003); http://dx.doi.org/10.1063/1.1544454 (3 pages)

Online Publication Date: 9 May 2003

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The effect of simultaneous substitution of Nd and Ca in the antiferromagnetic insulator, LaMnO3, is studied by x-ray diffraction, magnetoresistance, and magnetization measurements. X-ray powder diffraction patterns of La1−2xNdxCaxMnO3 polycrystalline bulk samples for x=0.2, 0.33, and 0.4 confirm the single-phase formation of orthorhombic perovskite structure (space group Pbnm). The unit cell volume decreases with increasing Nd/Ca substitution. Changes in the temperature dependence of resistivity from semiconducting to metallic, and an increase of the ferromagnetic transition temperature, are observed in this series with increasing x. For x=0.2, 0.33, and 0.4, the metal-insulator transition temperature (Tp) is 72, 140, and 155 K, respectively, and the magnetoresistance (MR) observed in this system in 2 T applied magnetic field around Tp is 35%, 99% and 65%, respectively. The MR of 99% for the x=0.33 sample is promising for practical device applications where MR at low fields is of special interest. The magnetic moment values, obtained from the magnetization data in the magnetically ordered state, agree reasonably well with the free ion Mn moments for all the samples. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.47.Lx Magnetic oxides
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Cr Saturation moments and magnetic susceptibilities

Unusual electronic transport properties in La0.96−xNdxK0.04MnO3

Yongquan Guo, Sujoy Roy, Naushad Ali, Xinhui Zhang, and Roger Wäppling

J. Appl. Phys. 93, 8089 (2003); http://dx.doi.org/10.1063/1.1544482 (3 pages)

Online Publication Date: 9 May 2003

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Polycrystalline La0.96−xNdxK0.04MnO3 has been studied by means of x-ray powder diffraction, dc magnetization, and electrical resistance measurement. La0.96−xNdxK0.04MnO3 initially crystallizes in a rhombohedral distorted perovskite structure. However, an orthorhombic structure is obtained with increasing Nd content more than 20%. Both the rhombohedral and the orthorhombic phases show ferromagnetic order. However, the compound shows a magnetic inhomogeneity behavior with increasing Nd content. With increasing Nd doping, the ferromagnetic order is significantly weakened, and the second magnetic transition occurs at a low temperature and its peak intensity enhances. The resistivity of these compounds also exhibits an imhomogeneity behavior. The rhombohedral phase shows a metal–insulator (MI) transition but the MI transition peak intensity is obviously weakened and broadens with increasing Nd content and a low temperature insulator state is observed in the orthorhombic phase. It is interesting that the second magnetoresistance ratio peak appears at low temperature. It might be due to Nd induced low temperature phase separation between the ferromagnetic metallic and antiferromagnetic insulating state. © 2003 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.K- Solid-solid transitions

Magnetic transition and large low-field magnetoresistance near Curie temperature in polycrystalline La2/3A1/3MnO3 (A=Ca,Sr)

Run-Wei Li, Ji-Rong Sun, Qing-An Li, Tao Zhu, Shao-Ying Zhang, and Bao-Gen Shen

J. Appl. Phys. 93, 8092 (2003); http://dx.doi.org/10.1063/1.1556940 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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By means of electron spin resonance, magnetization, and resistivity measurements, phase separation and a large low-field magnetoresistance (MR) accompanied by a first-order metamagnetic transition in the vicinity of Curie temperature (TC) were observed in polycrystalline La2/3Ca1/3MnO3, but were not observed in polycrystalline La2/3Sr1/3MnO3. It is obvious that the phase separation and large low-field MR near the TC are not universal features of the colossal MR materials. By combining the magnetic field dependence of magnetization and resistance, it was suggested that the first-order metamagnetic transition from the paramagnetic to ferromagnetic state induced by a magnetic field should be responsible for the large low-field MR observed in polycrystalline La2/3Ca1/3MnO3. Undoubtedly, this observation is very important for exploring large low-field MR in high temperature, which is necessary for practical application of the colossal magnetoresistance effect. © 2003 American Institute of Physics.
Show PACS
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.40.-s Critical-point effects, specific heats, short-range order
76.30.-v Electron paramagnetic resonance and relaxation
64.75.-g Phase equilibria
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
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