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  • 1
    Electronic Resource
    Electronic Resource
    Transport and magnetic properties of polycrystalline Nd1.85Ce0.15CuO4−y under applied magnetic fields : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6639-6641 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Systematic studies of transport and magnetic properties on polycrystalline Nd1.85Ce0.15CuO4−y specimens under applied magnetic fields as high as 8 kOe have revealed strong evidence of granularity in this system. Electrical resistivity measurements show two superconducting transitions. One of the transitions occurs at higher temperature and is almost insensitive to applied magnetic field and current density, while the other one occurs at lower temperature and is strongly modified by the application of magnetic field and changes in the current density. In the low-field limit (H〈100 Oe), a drastic broadening of the superconducting transition is observed. Magnetic susceptibility χac measurements show similar features. There are two well-defined contributions to the diamagnetic signal below 20 K which are particularly evident in the resistive component of χac where two peaks can be identified. The application of an applied magnetic field shifts both peaks towards low temperatures. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between superconducting islands. The islands have a superconducting transition at higher temperature, and the long-range order phase coherence is achieved through Josephson coupling at lower temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352539
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  • 2
    Electronic Resource
    Electronic Resource
    Cation distribution and intrinsic magnetic properties of Co-Ti-doped M-type barium ferrite (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1614-1623 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural and magnetic properties of BaFe12−2xCoxTixO19 (0≤x≤1.0) M-type barium ferrite have been investigated by means of neutron powder diffraction and high-field magnetization measurements. The cationic distribution and magnetic moments of the five different metallic sublattices are determined and compared to the experimental saturation magnetization. It is found that about 50% of Co ions occupy tetrahedral sites, thus being ineffective in the reduction of the uniaxial magnetic anisotropy, while Ti ions prefer the 4fVI octahedral sites. All in all, a clear hierarchy of sublattice preferences is defined. Although the collinearity of the magnetic structure is progressively broken, mainly above x≈0.7, the overall behavior remains ferrimagnetic. The strong local spin canting is tentatively attributed to the localization of diamagnetic Ti ions in the 4fVI octahedral sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349526
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic transitions in Pr2NiO4 single crystal : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6329-6331 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of a stoichiometric Pr2NiO4 single crystal have been examined by means of the temperature dependence of the complex ac susceptibility and the isothermal magnetization in fields up to 200 kOe at T=4.2 K. Three separate phases have been identified and their anisotropic character has been analyzed. A collinear antiferromagnetic phase appears first between TN = 325 K and Tc1 = 115 K, where the Pr ions are polarized by an internal magnetic field. At Tc1 a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P42/ncm). This magnetic transition has a first-order character and involves both the out-of-plane and the in-plane spin components (magnetic modes gx and gxcyfz, respectively). A second magnetic transition having also a first-order character is also clearly identified at Tc2 = 90 K which corresponds to a spin reorientation process (gxcyfz to cxgyaz magnetic modes). It should be noted as well that the out-of-phase component of χac shows a peak around 30 K which reflects the coexistence of both magnetic configurations in a wide temperature interval. Finally, two field-induced transitions have been observed at 4.2 K when the field is directed along the c axis. We propose that the high-field anomaly arises from a metamagnetic transition of the weak ferromagnetic component, similarly to La2CuO4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349958
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Spin glass transition in BaCo6Ti6O19 : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6172-6174 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermomagnetic ac and dc measurements were carried out on polycrystalline BaCo6Ti6O19. The system shows all the characteristic signatures of the spin glass syndrome. dc magnetic susceptibility displays a sharp peak at Tf = 13.6 K and below this temperature a clear onset of irreversibility between the zero field cooled and field cooled (ZFC–FC)processes is observed. The real part of the ac susceptibility shows also a sharp peak at Tf which strongly depends on the frequency of the ac magnetic field. The dynamic critical behavior of the system is studied by analyzing the imaginary part of the ac susceptibility in the scope of two models: the activated dynamic scaling and the equilibrium phase transition scaling. The best data collapsing is obtained assuming that a true phase transition occurs at the freezing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350034
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  • 6
    Electronic Resource
    Electronic Resource
    Spin glass-like behavior in Fe-doped Bi4Sr8Cu5O19+x insulating perovskite : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6184-6186 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline samples of the tubular phase Bi4Sr8Cu5O19+x with Fe ions substituting the Cu positions have been prepared up to a maximum content of 2 Fe ions per unit formula. The electrical and magnetic properties of these oxides have been examined and it is shown that they are insulating and present a complex magnetic behavior. It is found that the Fe ions have a localized magnetic moment displaying a Curie–Weiss law at high temperatures while below T≈100 K antiferromagnetic correlations are detected. From the evaluation of the effective paramagnetic moment and its composition dependence it is deduced that Fe doping induces a paramagnetic moment in some Cu ions which then contribute also to the temperature dependent paramagnetism. Finally, at lower temperatures (T〈25 K) a susceptibility peak is observed signaling a freezing of the magnetic moments. We suggest a spin-glass behavior associated either to a clustering of Fe ions or to the development of correlated domains interacting through the strongly correlated copper ions. We point out that the weak sensitivity of the resistivity on the Fe concentration gives further support to the hypothesis of some Fe clustering within the tubular crystal structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350012
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Transport and magnetic properties of Tl2Mn2−xRuxO7 diluted system (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5405-5407 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic and transport properties of Tl2Mn2−xRuxO7 pyrochlores are analyzed as a function of the substitution rate (0≤x≤2). For x≤0.2, the system exhibits colossal magnetoresistance (CMR) and ferromagnetic ordering. For higher doping rates CMR is completely washed out and the transport properties mimics that of the Tl2Ru2O7 pure compound with a semiconductor-to-metal transition at a temperature that decreases as x increases. The magnetic frustration progressively increases signalling the increase of antiferromagnetic interactions and the geometrical frustration intrinsic to the pyrochlore structure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369992
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  • 9
    Electronic Resource
    Electronic Resource
    Plastic deformation in high critical current melt-textured YBa2Cu3O7 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5515-5517 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of high-temperature creep under different conditions in melt-textured YBa2Cu3O7–Y2BaCuO5 composites, with high critical currents before deformation, is investigated. Transmission electron microscopy studies show that the low-temperature oxygenation process causes a strong modification of the as-deformed microstructure and leads to a clear degradation of the superconducting performances. This behavior of the superconducting properties is well correlated with the formation of extended planar defects such as large stacking faults and microcracks that severely diminish the vortex cutting length, thus enhancing the thermal activation effects on the critical currents and the irreversibility line. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363484
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  • 10
    Electronic Resource
    Electronic Resource
    The metamagnetic and the weak ferromagnetic transitions of the Cu lattice of Ho2CuO4 (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4608-4614 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the magnetic properties of the Cu lattice of Ho2CuO4. This cuprate can only be synthesized at high pressure. It crystallizes in a structure derived from the Nd2CuO4-type structure (T′ phase), modified by local distortions in the CuO2 planes. We have measured dc magnetization versus temperature and isothermal dc magnetization versus magnetic field. These measurements were made in the range of temperature from 5 to 540 K applying magnetic fields up to ±50 kOe. ac susceptibility has also been measured in the range of temperatures from 80 to 320 K, using different frequencies between 33 and 1000 Hz and excitation fields between 1 and 10 Oe. We have found a three-dimensional antiferromagnetic (AF) ordering of the Cu lattice of Ho2CuO4 below TN=271(1) K. This AF order is accompanied by a weak ferromagnetic (WF) component, due to a small canting of the Cu spins away from perfect AF alignment. Below TN, at zero field, the interlayer AF coupling makes the WF components in neighboring CuO2 planes to be oriented antiferromagnetically and, thus, to remain almost compensated. Only above a field-induced metamagnetic transition is the weak ferromagnetism evidenced. The WF component persists above TN, in a large temperature interval, induced by the magnetic field. The magnetization of the paramagnetic (PM) Ho lattice, which follows a Curie–Weiss law with μeff=10.16(1)μB/Ho atom and θ=7.6(5) K, is superimposed to the magnetism of the Cu lattice. There exists an exchange coupling between both lattices and the PM Ho ions are polarized through an internal magnetic field due to the WF component of the Cu moments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359806
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