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The powder alignment method is used to investigate the anisotropic physical properties of the weak-ferromagnetic superconductor system RuSr2RCu2O8 (R = Pr, Nd, Sm, Eu, Gd, Gd0.5Dy0.5). The RuSr2GdCu2O8 cuprate is a weak-ferromagnetic superconductor with a magnetic ordering of Ru moments at TN(Ru) = 131 K, a superconducting transition in the CuO2 layers at Tc = 56 K, and a low temperature Gd antiferromagnetic ordering at TN(Gd) = 2.5 K. Due to weak magnetic anisotropy of this tetragonal system, highly c-axis aligned microcrystalline powder (diameter ~ 1-10 $\mu$m) in epoxy can be obtained only for R = Eu and Gd through the field-rotation powder alignment method where c-axis is perpendicular to the aligned magnetic field Ba = 0.9 T and parallel to the rotation axis. For smaller rare earth compound R = Gd0.5Dy0.5, powder alignment can be achieved using the simple field powder alignment method where c-axis is partially aligned along the aligned magnetic field. The anisotropic temperature dependence of magnetic susceptibility for the c-axis aligned powders exhibit weak anisotropy with $\chi_{c} > \chi_{ab}$ at room temperature due to anisotropic rare earth, Eu and Gd, contribution and crossover to $\chi_{c} < \chi_{ab}$ below 190 K where strong Ru anisotropic short-range exchange interaction overtakes the rare earth contribution. Anisotropic diamagnetic superconducting intragrain shielding signal of aligned microcrystalline RuSr2GdCu2O8 powder-in-epoxy below vortex lattice melting temperature at 39 K in 1-G field is much weaker than the intergrain polycrystalline bulk sample signal due to the small grain size (d ~ 1-10 $\mu$m), long penetration depth ($\lambda_{ab}$ ~ 0.55 $\mu$m, $\lambda_{c}$ ~ 0.66 $\mu$m) and the two-dimensional (2D) character of CuO2 layers., Comment: 6 pages, 13 figures

Similar to the optimal-doped, weak-ferromagnetic (WFM induced by canted antiferromagnetism, T$_{Curie}$ = 131 K) and superconducting (T$_{c}$ = 56 K) RuSr$_{2}$GdCu$_{2}$O$_{8}$, the underdoped RuSr$_{2}$EuCu$_{2}$O$_{8}$ (T$_{Curie}$ = 133 K, T$_{c}$ = 36 K) also exhibited a spontaneous vortex state (SVS) between 16 K and 36 K. The low field ($\pm$20 G) superconducting hysteresis loop indicates a weak and narrow Meissner state region of average lower critical field B$_{c1}^{ave}$(T) = B$_{c1}^{ave}$(0)[1 - (T/T$_{SVS}$)$^{2}$], with B$_{c1}^{ave}$(0) = 7 G and T$_{SVS}$ = 16 K. The vortex melting transition (T$_{melting}$ = 21 K) below T$_{c}$ obtained from the broad resistivity drop and the onset of diamagnetic signal indicates a vortex liquid region due to the coexistence and interplay between superconductivity and WFM order. No visible jump in specific heat was observed near T$_{c}$ for Eu- and Gd-compound. This is not surprising, since the electronic specific heat is easily overshadowed by the large phonon and weak-ferromagnetic contributions. Furthermore, a broad resistivity transition due to low vortex melting temperature would also lead to a correspondingly reduced height of any specific heat jump. Finally, with the baseline from the nonmagnetic Eu-compound, specific heat data analysis confirms the magnetic entropy associated with antiferromagnetic ordering of Gd$^{3+}$ (J = S = 7/2) at 2.5 K to be close to $\it{N_{A}k}$ ln8 as expected., Comment: 7 figures

Based on the magnetoresistance, magnetization, ultrasound, and crystallographic data, we studied the role of the cooperative Jahn-Teller effect in the charge ordered (CO) state for La1-xCaxMnO3. We found that, with increasing the fraction of Q3 mode of Jahn-Teller distortion and decreasing that of Q2 mode in the CO state, the magnetic structure evolves from CE-type to C-type and the orbital ordering changes from 3d(x2-r2)/3d(y2-r2)-type to 3d(x2-z2)-type, with the strength of ferromagnetism and the phase separation tendency being suppressed. At the same time, the stability of the CO state and the cooperative Jahn-Teller lattice distortion increase. These effects imply that the cooperative Jahn-Teller effect with different vibration modes is the key ingredient in understanding the essential physics of the CO state., 10 pages, 2 figures. To appear on Applied Physics Letters