Percolative phase separation induced by nonuniformly distributed excess oxygens

The zero-field $^{139}$La and $^{55}$Mn nuclear magnetic resonances were studied in $\rm La_{0.8}Ca_{0.2}MnO_{3+\delta}$ with different oxygen stoichiometry $\delta$. The signal intensity, peak frequency and line broadening of the $^{139}$La NMR spectrum show that excess oxygens have a tendency to concentrate and establish local ferromagnetic ordering around themselves. These connect the previously existed ferromagnetic clusters embedded in the antiferromagnetic host, resulting in percolative conduction paths. This phase separation is not a charge segregation type, but a electroneutral type. The magnetoresistance peak at the temperature where percolative paths start to form provides a direct evidence that phase separation is one source of colossal magnetoresistance effect.Comment: 4 pages, 5 figure

Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in Ni81_{81}Fe19_{19} / α\alpha-Fe2_2O3_3

We report studies of exchange bias and coercivity in ferromagnetic Ni$_{81}$Fe$_{19}$ layers coupled to antiferromagnetic (AF) (0001), (11$\bar{2}$0), and (11$\bar{0}$2) $\alpha$-Fe$_2$O$_3$ layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show for the first time that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let

Formation of finite antiferromagnetic clusters and the effect of electronic phase separation in Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}

We report the first experimental evidence of a magnetic phase arising due to the thermal blocking of antiferromagnetic clusters in the weakened charge and orbital ordered system Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}. The third order susceptibility (\chi_3) is used to differentiate this transition from a spin or cluster glass like freezing mechanism. These clusters are found to be mesoscopic and robust to electronic phase separation which only enriches the antiphase domain walls with holes at the cost of the bulk, without changing the size of these clusters. This implies that Al substitution provides sufficient disorder to quench the length scales of the striped phases.Comment: 4 Post Script Figure

Weak charge-ordering behavior in phase separated (Ln1/3Sm2/3)2/3Ca1/3MnO3 (Ln=Pr and La) manganites

We have studied a weak charge-ordering behavior in phase separated (Ln1/3Sm2/3)2/3Ca1/3MnO3 (Ln=Pr and La) manganites with same hole doping but slightly different tolerance factors. The M(T) and ρ(T) curves of the Pr-sample showed an anomaly caused by a weak charge-order (CO) transition at not, vert, similar210 K, while that of La-sample did not. However, the La-sample displayed a weak anomaly related to the CO instability in the derivative curve of the temperature dependent magnetoresistance. This result is understood on the basis that the CO phase in La-sample is partly suppressed by a large magnetic field of not, vert, similar80 kOe, while in Pr-sample it is not collapsed in that field scale. Our data support the existence of charge-ordering, electronic phase separation and a field-induced reduction of weak CO instability for La-sample, which can contribute towards high MR especially at lower temperatures due to partial melting of CO phase and/or percolation behavior

The alternative route of low-temperature preparation of highly oriented lead zirconate titanate thin films by high gas-pressure processing

The Pb(ZrxTi1-x)O-3 (PZT) films sputter deposited oil LaNiO3(LNO)/Si(100) substrates were recrystallized to highly (100)-oriented perovskite Structure by high oxygen-pressure processing, (HOPP) and high argon-pressure processing (HAPP), which were performed at a relatively low temperature 400 degrees C compared to the normally required temperature condition above 600 degrees C. Ferroclectricity of PZT films was investigated by a measurement of P-E hysteresis loop. The P-E hysteresis loops of the PZT(52/48) and PZT(30/70) films after HOPP showed better squareness and larger remnant polarization than those of as-sputtered ones prepared at a high temperature of 600 degrees C. Although the PZT films with HAPP also showed a high (100)-oriented perovskite structure and obvious ferroelectricity, their P-E loops suggested relatively poor ferroelectricity compared to those of the PZT films with HOPP. This means that a further optimization for HAPP is needed to improve ferroelectricity of PZT films

Experimental evidence for mixed-valent Cr ions in half-metallic CrO2: Temperature-dependent XMCD study

By employing soft X-ray magnetic circular dichroism (XMCD) and soft X-ray absorption spectroscopy (XAS), we have investigated the temperature (T)-dependent valence and spin states of Cr ions in half-metallic ferromagnet CrO2 nanorod powder. The lineshape-analysis of both the Cr 2p XAS and XMCD spectra of CrO2 reveals that the Cr ions in bulk CrO2 have both Cr4+ (t(2g)(2)up arrow) and Cr3+ (t(2g)(3)up arrow) valence configurations. This work provides the direct experimental evidence for the Cr3+-Cr4+ mixed-valent states in bulk CrO2 (Cr3.8+), demonstrating that the half-metallic ferromagnetism in CrO2 originates from the double-exchange interaction. The T-dependent intensity variation of the Cr 2p XMCD spectrum agrees well with the bulk magnetization M(T) and the Curie temperature, indicating that the measured Cr 2p XMCD data represent the intrinsic bulk ferromagnetism in CrO2, and support the above finding of the XMCD lineshape analysis. (C) 2017 Elsevier B.V. All rights reserved.11sciescopu

Magnetic Transition and Long-Time Relaxation Behavior Induced by Selective Injection of Guest Molecules into Clathrate Hydrates

Magnetic molecules physisorbed into low-dimensional nanostructures of microporous materials such as graphite and metal-organic frameworks have been verified to exhibit an unusual magnetic behavior. We demonstrate that the selective injection of both magnetic and nonmagnetic guest molecules into the water-ice cages of clathrate hydrates to form a 3D superstructure with tetrahedral and diamond-like sublattices can modify the inherent magnetism.close6