O. F. de Lima

Spin glass behavior in RuSr 2 Gd 1.5 Ce 0.5 Cu 2 O 10 − δ

The dynamics of the magnetic properties of polycrystalline RuSr 2 Gd 1 . 5 Ce 0 . 5 Cu 2 O 1 0 - δ (Ru-1222) have been studied by ac susceptibility and dc magnetization measurements, including relaxation and ageing studies. Ru-1222 is a reported magnetosuperconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity in Cu-O 2 planes below T c ∼40 K. The exact nature of Ru spins magnetic ordering is still being debated, and no conclusion has been reached yet. In this work, a frequency-dependent cusp was observed in Χ a c vs T measurements, which is interpreted as a spin glass transition. The change in the cusp position with frequency follows the Vogel-Fulcher law, which is commonly accepted to describe a spin-glass with magnetically interacting clusters. Such an interpretation is supported by thermoremanent magnetization (TRM) measurements at T=60 K. TRM relaxations are well described by a stretched exponential relation, and present significant aging effects.

Anisotropic superconducting properties of aligned MgB2 crystallites

Samples of aligned MgB(2) crystallites have been prepared, allowing for the first time the direct identification of an upper critical field anisotropy H(ab)(c2)/H(c)(c2) = xi(ab)/xi(c) approximately 1.7, with xi(o,ab) approximately 70 A, xi(o,c) approximately 40 A, and a mass anisotropy ratio m(ab)/m(c) approximately 0.3. A ferromagnetic background signal was identified, possibly related to the raw materials purity.

Specific heat at low temperatures and magnetic measurements inNd0.5Sr0.5MnO3andR0.5Ca0.5MnO3(R=Nd,Sm, Dy, and Ho) samples

We studied the magnetization as a function of temperature and magnetic field in the compounds

Effect of Zn substitution on para- to ferromagnetic transition temperature in La0.67Ca0.33Mn1−xZnxO3 colossal magnetoresistance materials

{\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3},

Magnetic phase evolution in the LaMn1−xFexO3+y system

{\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},

Structural and superconducting properties of LaBaCaCu3O7+δ system: a neutron diffraction study

{\mathrm{Sm}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},

Exponential critical state model applied to ac susceptibility data for the superconductor YBa2Cu3O7−δ

{\mathrm{Dy}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},