Possible competition between superconductivity and magnetism in RuSr<SUB>2</SUB>Gd<SUB>1.5</SUB>Ce<SUB>0.5</SUB>Cu<SUB>2</SUB>O<SUB>10-&#948;</SUB> ruthenocuprate compounds

The RuSr2Gd1.5Ce0.5Cu2O10-&#948; (Ru-1222) compounds, with varying oxygen content, crystallize in a tetragonal crystal structure (space group I4/mmm). Resistance (R) versus temperature (T) measurements show that the air-annealed samples exhibit superconductivity with superconduting transition temperature (Tc) onset at around 32 K and R=0 at 3.5 K. On the other hand, the N2-annealed sample is semiconducting down to 2 K. Magneto-transport measurements on an air-annealed sample in applied magnetic fields of 3 and 6 T (Tesla) show a decrease in both Tc onset and TR=0. Magnetoresistance of up to 20% is observed in the N2-annealed sample at 2 K and 3 T applied field. The dc magnetization data (M vs T) reveal magnetic transitions (Tmag) at 100 K and 106 K, respectively, for both air- and N2-annealed samples. Ferromagnetic components in the magnetization are observed for both samples at 5 K and 20 K. The superconducting transition temperature (Tc) seems to compete with the magnetic transition temperature (Tmag). Our results suggest that the magnetic ordering temperature (Tmag) of Ru moments in RuO6 octahedra may have direct influence/connection with the appearance of superconductivity in Cu-O2 planes of Ru-1222 compounds

Structure, magnetic and transport properties of Ti-substituted La0.7Sr0.3MnO3

Ti-substituted perovskites, La0.7Sr0.3Mn1-xTixO3, with x between 0 to 0.20, were investigated by neutron diffraction, magnetization, electric resistivity, and magnetoresistance (MR) measurements. All samples show a rhombohedral structure (space group R3c) from 10 K to room temperature. At room temperature, the cell parameters a, c and the unit cell volume increase with increasing Ti content. However, at 10 K, the cell parameter a has a maximum value for x = 0.10, and decreases for x greater than 0.10, while the unit cell volume remains nearly constant for x greater than 0.10. The average (Mn,Ti)-O bond length increases up to x=0.15, and the (Mn,Ti)-O-(Mn,Ti) bond angle decreases with increasing Ti content to its minimum value at x=0.15 at room temperature. Below the Curie temperature T_C, the resistance exhibits metallic behavior for the x _ 0.05 samples. A metal (semiconductor) to insulator transition is observed for the x_ 0.10 samples. A peak in resistivity appears below T_C for all samples, and shifts to a lower temperature as x increases. The substitution of Mn by Ti decreases the 2p-3d hybridization between O and Mn ions, reduces the bandwidth W, and increases the electron-phonon coupling. Therefore, the TC shifts to a lower temperature and the resistivity increases with increasing Ti content. A field-induced shift of the resistivity maximum occurs at x less than or equal to 0.10. The maximum MR effect is about 70% for La0.7Sr0.3Mn0.8Ti0.2O3. The separation of TC and the resistivity maximum temperature Tmax enhances the MR effect in these compounds due to the weak coupling between the magnetic ordering and the resistivity as compared with La0.7Sr0.3MnO3.Comment: zip fil

Fingerprint of phase transition across the magnetic compensation temperature in Pr_1-xGd_xAl₂ alloys

The magnetization compensation phenomenon is observed for Sm1-xNdxScGe at x=0.09 at a temperature &#8764;90 K in a small applied magnetic field, which establishes the &#8216;spin surplus&#8217; status of magnetic moment of Sm in the host matrix. We also noted that the sample profiles in QD SQUID magnetometer become asymmetric in some situations indicating significant contributions from multiple moments higher than the dipole moment. We have successfully accounted for them using a fitting procedure the higher order magnetic moments

Phase separations in La<SUB>0.7-x</SUB>Dy<SUB>x</SUB>Ca<SUB>0.3</SUB>Mn(Fe)O<SUB>3</SUB>

Mossbauer spectroscopy of La0.7-xDyxCa0.3Mn(Fe)O3 shows phase separation, both above and below TC. The behavior in the two regions are independent and related to different phenomena. Above TC, the phase splitting is due to different lattice distortions. In one of the phases, Jahn-Teller distortion is significant. Below TC, the spin orderings in the two phases are ferromagnetic (FM) and spin glass (SG) orderings, respectively. At low temperatures, SG phase converts into FM phase when the applied magnetic field increases, but only partially. We find a drastic increase in magnetoresistivity (MR) as x is increased beyond 0.07. It attains a maximum value for x&#8776;0.12 (greater than750 000%) and decreases again rapidly as x increases. We have provided an explanation for the high MR in x=0.12 phase. Other differences between the compositions studied here can also be identified. First, the phase with Jahn-Teller distortion disappears when the temperature is lowered to TC in a composition with x 0.12. This is not the case when x=0.07. Second, we observe anomalous hysteresis loop when x=0.12. The anomaly is less pronounced in other compositions. Third, in composition x=0.07, the hyperfine magnetic fields (Hint) in FM and SG components are distinctly different. This is not so when x=0.12

New features in rare earth based zero magnetization spin ferromagnets

A ferromagnetic rare earth (RE) intermatallic can be made to imbible zero magnetization characteristic and display magnetic reorientation phenomenon by letting a RE site be occupied at random by two RE atoms belonging to different halves of 4f series (Gd to be counted alongwith second half) and choosing their fractional compositions appropriately. In recent times, H. Adachi and co-workers drew specific attention to ferromagnetic Sm based systems, where the net moment can be either &#8216;orbital surplus&#8217;, or &#8216;spin surplus&#8217; (due to admixture effects) and the zero magnetization state can be obtained by substitution of Sm by the Gd or Nd. We present here a status report of our investigations and describe newer features related to magentic compensation phenomenon in a wide variety of RE system. In particular, our studies reveal that (i) the notion of spin flip transition across the temperature region of magnetic compensation is a generic behavior, (ii) it can happen in a re-entrant manner in specific circumstances, (iii) it survives strong hybridization effects that can happen for Ce3+ ions, e.g., in CeRh3B2, and compromise ferromagnetic exchange interaction between diddimilar RE spins, etc