The possible origin of the higher magnetic phase transition in RuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222)

Two magnetic transitions are observed in the magneto-superconducting RuEu2-xCexSr2Cu2O10 (Ru-1222), at TM 160 K and TM2~80 K. Below TM2 the Ru moments are weak-ferromagnetically ordered and wide ferromagnetic hysteresis loops are observed, they become narrow and disappear at ~ 60-70 K. Above TM2, (i) small antiferromagnetic-like hysteresis loops reappear with a peak in the coercive fields around 120 K. (ii) A small peak at ~120 K is also observed in the dc and ac susceptibility curves. The two phenomena are absent in the non-SC x=1 samples. For x<1, the decrease of the Ce4+ content, is compensated by non-homogeneous oxygen depletion, which may induce a reduction of Ru5+ ions to Ru4+. The higher ordering temperature, TM, which does not change with x, may result from Ru4+ rich clusters, in which the Ru4+-Ru4+ exchange interactions are stronger than the Ru5+-Ru5+ interactions. In the superconducting Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10 (x=0-0.4) system, TM2 shifts to low temperature with x (14 K for x=0.4), whereas TM is not affected by the Mo content, indicating again that TM may not correspond to the main phase. Two scenarios are suggested to explain the magnetic phenomena at TM2<T< TM. (i) They are due to a small fraction of nano-size islands inside the crystal grains, in which the Ru4+ concentration is high and are magnetically ordered below TM. (ii) The presence of nanoparticles of a foreign minor extra Ru4+ magnetic phase of Sr-Cu-Ru-O3, which orders at TM, in which Cu is distributed inhomogeneously in both the Ru and Sr sitesComment: 11 pages, 10 figure

Magnetic phase transitions in SmCoAsO

Magnetization, x-ray diffraction and specific-heat measurements reveal that SmCoAsO undergoes three magnetic phase transitions. A ferromagnetic transition attributed to the Co ions, emerges at TC=57 K with a small saturation moment of 0.15muB/Co. Reorientation of the Co moment to an antiferromagnetic state is obtained at TN2=45 K. The relative high paramagnetic effective moment Peff=1.57 MuB/Co indicates an itinerant ferromagnetic state of the Co sublattice. The third magnetic transition at TN1=5 K is observed clearly in the specific-heat study only. Both magnetic and 57Fe Mossbauer studies show that substitution of small quantities of Fe for Co was unsuccessful.Comment: 10pages text+Figures: comments welcome ([email protected]

Magnetization study of RuSr2Y1.5Ce 0.5Cu2O10 (Ru-1222)

We have studied the magnetic properties of the non-superconducting RuSr2Ln1.5Ce0.5Cu2O10 (Ln=Y, Dy and Ho, Ru-1222) compounds synthesized under high pressure (6 Gpa) at elevated temperature. The materials become magnetically ordered at TM =152(2) K regardless of Ln. The wide ferromagnetic-like hysteresis loops which open at 5 K, close themselves around Tirr= 90-100 K and the remanent magnetizations (Mrem) and the coercive fields (HC) become zero. Surprisingly, at Tirr<T< TM a reappearance of the Mrem and HC (with a peak at 120-130 K) is observed for all three samples studied. For the non-magnetic Ln=Y compound, the extracted saturation moment at 5 K and the effective paramagnetic moment are is 0.75 and 2.05 mB /Ru, values which are close to the expected 1 mB and 1.73 mB respectively, for the low-spin state of Ru5+. We argue that the Ru-1222 system becomes (i) anti-ferromagnetically (AFM) ordered at TM. In this range a metamagnetic transition is induced by the applied field (ii). At Tirr < TM, weak-ferromagnetism (W-FM) is induced by the canting of the Ru moments.Comment: 15 pages of text with figure. Submitted to Phys. Rev.

Self doping effect and successive magnetic transitions in superconducting Sr2_2VFeAsO3_3

We have studied a quinary Fe-based superconductor Sr$_2$VFeAsO$_3$ by the measurements of x-ray diffraction, x-ray absorption, M\"{o}ssbauer spectrum, resistivity, magnetization and specific heat. This apparently undoped oxyarsenide is shown to be self doped via electron transfer from the V$^{3+}$ ions. We observed successive magnetic transitions within the VO$_2$ layers: an antiferromagnetic transition at 150 K followed by a weak ferromagnetic transition at 55 K. The spin orderings within the VO$_2$ planes are discussed based on mixed valence of V$^{3+}$ and V$^{4+}$.Comment: One Table and more references are adde

Testing the influence of acceleration on time dilation using a rotating M\"Ossbauer absorber

The aim of the experiment series was to test the influence of acceleration on time dilation by measuring the relative spectral shift between the resonance spectra of a rotating Mossbauer absorber with acceleration anti-parallel and parallel to the direction of the incident beam. Based on the experiences and know-how acquired in our previous experiments, We collected data for rotation frequencies up to 510Hz in both directions of rotation and also used different slits. For each run with high rotation, we observed a stable statistically significant relative shift between the spectra of the two states with opposite acceleration. This indicates the influence of acceleration on time dilation. However, we found that this shift also depends on the choice of the slit, and on the direction of rotation. These new unexpected findings, resulting from the loss of symmetry in obtaining the resonant lines in the two states, could overshadow the relative shift due to acceleration. This loss of the symmetry is caused by the deflection of the radiative decay due to the Nuclear Lighthouse effect from the rotating Mossbauer absorber. We also found that it is impossible to keep the alignment (between the optical and the dynamical rotor systems) with accuracy needed for such experiment, for long runs, which resulted in the reduction of the accuracy of the observed relative shift. These prevent us to claim with certainty the influence of acceleration on time dilation using the currently available technology. An improved KB optics with focal spot of less than 1 micron to avoid the use of a slit and a more rigid mounting of the rotor system, are necessary for the success of such experiment. Hopefully, these findings together with the indispensable plan for a conclusive experiment presented in the paper, will prove useful to future experimentalists wishing to pursue such an experiment