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  • 1
    Electronic Resource
    Electronic Resource
    Weak ferromagnetism induced by the external field above TN in GdzCuO4 : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5710-5712 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of the temperature and field dependence of the dc magnetization near the antiferromagnetic (AF) transition in Gd2CuO4 shows the presence of field-induced weak ferromagnetism (WF) well above the Néel temperature TN. ac susceptibility measurements indicate TN=266(3) and 282(3) K, for single crystals and ceramic samples, respectively. The shift of the electron-spin-resonance line of the Gd3+ ions as a function of temperature T, δHr(T), is compared with the static internal field Hi(T), which describes the coupling between the paramagnetic Gd lattice and the WF component of the Cu moments. Both δHr(T) and Hi(T) show that the WF persists up to ≈50 K above TN. The initial susceptibility (for H≤100 G) presents a contribution in excess of the paramagnetism of Gd ions. For T≥TN, it decays as K(T−TN)−1, with K=0.20(3) emu K mol. The relationship between this result and the strong two-dimensional AF correlations in these cuprates is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353599
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  • 2
    Electronic Resource
    Electronic Resource
    Observation of an unusual ESR signal in antiferromagnetic Eu2CuO4 : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4872-4873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of an unusual electron spin resonance (ESR) signal in single crystals of Eu2CuO4. The signal appears to be associated with a resonance mode of the CuO2 planes, similar to the midfield and low-field absorptions we have reported previously [Phys. Rev. B 41, 1934 (1990)]. However, it is only observed when the projection of the applied dc magnetic field in the CuO2 plane is within a few degrees of the 〈110〉 crystallographic direction. Additionally the sample must be field cooled in the CuO2 plane, but with a component of the cooling field perpendicular to the 〈110〉 ESR observation direction. Both the field for resonance and the linewidth exhibit a 1/cos θ dependence, where θ is the angle of the applied dc field between the c axis and the 〈110〉 observation direction. Additional constraints for observation of the resonance are that the microwave rf magnetic field must have a component in the CuO2 plane, but perpendicular to the dc field. The signal disappears above ∼215 K, which we assume is associated with the antiferromagnetic ordering temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348208
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  • 3
    Electronic Resource
    Electronic Resource
    Weak ferromagnetism and spin-glass-like behavior in Tb2CuO4 : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6095-6097 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline Tb2CuO4 with tetragonal (T') structure was synthesized under high pressure. The in-phase component of the alternating-current (ac) susceptibility χ'(T) presents a peak whose onset at TN ≈ 290 K, we associate with antiferromagnetic ordering of the Cu moments. The shape of this peak is strongly dependent on the amplitude of the excitation field, indicating nonlinearity of the magnetization as a function of the applied magnetic field. The frequency dependence of the peak observed in χ'(T) and the nonzero out-of-phase component χ‘(T) in the same temperature range indicate the existence of relaxation processes associated with the development of a weak ferromagnetic component. Below ∼100 K, the relaxation becomes much slower than the frequency of the oscillating field and the ac susceptibility is dominated by the paramagnetic response of Tb ions, which follows a Curie–Weiss law. The direct-current (dc) magnetization presents a nonlinear dependence on the applied field for Ha (approximately-less-than) 2 kOe and shows thermomagnetic irreversibility below a second characteristic temperature Tirr 〈 TN. An additional peak at TL ≈ 10 K indicates a long range magnetic order of the Tb ions with a possible spin reorientation of the Cu moments. The thermal irreversibility and nonlinearity of the dc magnetization below Tirr, the relaxation processes revealed by the ac susceptibility, and the typical logarithmic decay of the remanent magnetization, point to the existence in this material of a weak ferromagnetic state with spin-glass-like characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350057
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  • 4
    Electronic Resource
    Electronic Resource
    Spin dynamics in perovskites, pyrochlores, and layered manganites (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5810-5812 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High temperature electron spin resonance (ESR) and magnetic susceptibility (χ) are analyzed for manganites related with colossal magnetoresistance (CMR). The properties of compounds with different crystalline structures: three-dimensional (3D) perovskites, pyrochlore, and La1.2Sr1.8Mn2O7, a two-dimensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature dependence of the ESR linewidth presents a universal behavior dominated by the variations of χ(T), ΔHpp(T)=[C/Tχ(T)]ΔHpp(∞). The high temperature limit of the linewidth, ΔHpp(∞), is related to the parameters of the Hamiltonian describing the interactions of the spin system. The role played by magnetic anisotropy, isotropic superexchange, and double exchange is revealed and discussed in the analysis of the experimental data. In CMR and non-CMR pyrochlores, ΔHpp(∞)∝ωp2/J where J is proportional to the Curie–Weiss temperature, including the hybridization mechanism producing CMR. Instead, ΔHpp(∞) of CMR perovskites seems not to be affected by the double-exchange interaction. In contrast with the 3D perovskites, the ESR linewidth and resonance field of La1.2Sr1.8Mn2O7, a bilayer compound, although isotropic at high temperatures, becomes anisotropic for Tc=125 K〈T〈Tp(approximate)450 K. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372530
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  • 5
    Electronic Resource
    Electronic Resource
    Weak ferromagnetic resonance of Gd2CuO4 small particles (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8612-8614 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microwave-absorption measurements have been performed in Gd2CuO4 particles of controlled size. We have measured the microwave absorption associated with a magnetic resonance of the weak-ferromagnetic component of the magnetization. The onset temperature of this signal, related to the appearance of weak ferromagnetism, is depressed when the particle size is decreased. A simultaneous depression of the Néel temperature is suggested as the origin of the observed dependence, due to the limitation on the two-dimensional correlation length imposed by the particle size. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362459
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between weak ferromagnetism, superconductivity, and lattice parameter in the A2−x−y〉BxCeyCuO4 (A,B≡La, Pr, Nd, Sm, Eu, Gd, Y) compounds : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6723-6725 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results obtained by x-ray, dc magnetization, ac magnetic susceptibility, microwave magnetic absorption, and electron paramagnetic resonance of the magnetic and superconductive properties of a large series of compounds of the form A2−x−yBxCeyCuO4 with A,B≡La, Pr, Nd, Sm, Eu, Gd, and Y. For y=0 antiferromagnetic ordering of the copper moments is present at TN≈280 K for all the compounds formed in the tetragonal T' phase. Weak ferromagnetism (WF) associated with the canting of the copper moments is observed in all the compounds with a lattice parameter, a〈a0, a0≈3.91 A(ring), regardless of the rare-earth (R) ions present in the system. Superconductivity is observed only in the Ce-doped compounds with a(approximately-greater-than)a1, a1≈3.92 A(ring). The maximum onset temperature Tc is found for a≈3.95 A(ring). A phase diagram was obtained by varying the lattice parameter size as a function of A, B, and x. The correlation between the appearance of WF in the undoped compounds and the disappearance of superconductivity in the Ce-doped systems is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356982
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  • 7
    Electronic Resource
    Electronic Resource
    Gd concentration dependence of the spin reorientation critical field in Eu2−xGdxCuO4 : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6577-6579 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ESR measurements of the microwave absorption signal associated with weak ferromagnetism in single crystals of Eu2−xGdxCuO4 are presented for X band (9.5 GHz) and L band (1.2 GHz) as a function of the Gd concentration. The strong absorption observed at low magnetic fields was interpreted, for samples with low Gd concentration, as due to a field-induced spin reorientation transition occurring at a critical field Hc, coincident with the in-plane magnetic anisotropy effective field Heffy. For larger x the Cu-Gd magnetic interaction needs to be considered leading to smaller Hc values. Our measurements show that for Gd concentrations in the range 0≤x≤1 the experimental data can be very well fitted with parameters derived from previous measurements. This fact indicates that these compounds have nearly the same in-plane anisotropy effective field, in spite of the small changes in lattice parameters. For x=2 lattice distortions increase causing an Hc larger than the expected one. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361950
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  • 8
    Electronic Resource
    Electronic Resource
    Structural and magnetic characterization of Co particles coated with Ag : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6564-6566 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Co fine particles coated with Ag have been synthesized through the microemulsion method in an inert atmosphere. The size of the particles is controlled by the water droplets of the microemulsions. Fine particles prepared by this method, consist of a magnetic core of Co covered by a layer of Ag. Samples containing from 3.3 to 40.5 vol % Co have been prepared. The average size of the particles obtained is in the nanometer range. The magnetic properties were studied by dc magnetization at 77 K and room temperature. The data show a strong dependence of the magnetic properties on the annealing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358195
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  • 9
    Electronic Resource
    Electronic Resource
    Dependence of the magnetic properties Gd2−xCexCuO4, 0≤x≤0.15, on their particle size : 38th Annual Conference ion Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6757-6759 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gd2−xCexCuO4, 0≤x≤0.15, have been synthesized by the solid state reaction, the sol-gel technique and the water-in-oil microemulsion, in order to vary the particle size. The samples have been characterized by x-ray diffraction, photon correlation spectroscopy and transmission electron microscopy. Magnetization and ac susceptibility measurements were performed between 4 and 300 K. The extrapolated linear part of the inverse magnetization shifts to lower temperatures as the particle size decreases. The internal field associated to the WF of the Cu moments diminishes with the particle diameter. Differences between the zero-field-cooling and the field-cooling magnetization curves were observed for T〈TN. These differences depend on the particle size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356844
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal treatment dependence of the dynamic magnetic behavior of Gd2CuO4 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1674-1677 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: dc and ac magnetization measurements in Gd2CuO4 ceramic samples synthesized at different annealing temperatures show that their magnetic properties are influenced by the thermal treatment. The changes consist of variations of the onset point for differences between zero field cooled and field cooled dc magnetizations, in the coercive fields, and in the position and frequency dependence of a maximum in the real part of ac susceptibility. An explanation suggesting a temperature-dependent homogeneity of the oxygen distortions causing weak ferromagnetism in the CuO2 planes is given. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362966
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