The longitudinal ultrasonic sound velocity and attenuation, the resistivity, and lattice parameters were studied as a function of temperature from 30 K to 300 K in La 1 − x Ca x MnO3 (0.5 ⩽ x ⩽ 0.9). For all the samples, a dramatic stiffening of the sound velocity below the charge ordering transition temperature TCO was directly driven by distinct changes of the lattice parameters due to the formation of long-range ordering of Jahn-Teller–distorted MnO 6 octahedra. The relative change of the sound velocity (ΔV/V) below TCO depends on the Ca concentration x and reaches the maximum at x = 0.75, implying that the effective strength of the electron-lattice interaction with the Jahn-Teller distortion is the strongest at x = 0.75 and hence the charge-ordered state is mostly stabilized near x = 0.75 and insensitive to the application of a magnetic field, which is supported by the charge transport properties under high magnetic fields up to 14 T.

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We report the rotating field entropy of ErFeO3 single-crystal in a temperature range of 3–40 K. The giant magnetic entropy change, ΔSM = −20.7 J/(kg K), and the refrigerant capacity, RC = 273.5 J/kg, are observed near T=6 K. The anisotropic constants at 6 K, K1 = 1.24× 103 J/kg, K2 = 0.74 × 103 J/kg, in the bc plane are obtained. By considering the magnetocrystalline anisotropy and Fermi-Dirac angular distribution along the orientation of spontaneous magnetization, the experimental results can be well simulated. Our present work demonstrates that ErFeO3 crystal may find practical use for low temperature anisotropic magnetic refrigeration.

The Jahn-Teller effect in the charge-ordered (CO) state for La 1-x Ca x MnO 3 (0.5≤x≤0.87) was studied by measuring the low-temperature powder x-ray diffraction, internal friction, and shear modulus. We find that the electron-lattice interaction with the static Jahn-Teller distortion is the strongest near x ≈ 0.75 in the CO state. It was particularly observed that a crossover of the Jahn-Teller vibration mode from Q 2 to Q 3 near x=0.75 induces crossovers of the crystal structure from tetragonally compressed to tetragonally elongated orthorhombic, and of the magnetic structure from CE-type to C-type near x=0.75. The experimental results give strong evidence that the Jahn-Teller effect not only plays a key role in stabilizing the CO state, but also determines the magnetic and crystal structures in the CO state for La 1-x Ca x MnO 3 . 1 It is well known that the La 1-x Ca x MnO 3 (0.5≤x≤0.87) manganites show charge, spin, and/or orbital orderings below the charge ordering transition temperature T CO [1], and much efforts have been devoted to this system to disclose the microscopic origin of the charge-ordered (CO) state [2,3]. It has been suggested that when the long-range Coulomb interaction and/or a strong electron-lattice interaction with the Jahn-Teller (JT) distortion overcomes the kinetic energy of e g electrons, real-space charge and concomitant spin and/or orbital orderings occur throughout the crystal structure. Despite many investigations have been done on this aspect, the main driving force of the CO state being the long-range Coulomb interaction or the electron-lattice interaction with the JT effect or both is still a subject of discussion [3,4]. Recent experimental observation of "wigner-crystal" CO state from transmission electron microscopy, synchrotron x-ray and neutron diffractions on La 0.33 Ca 0.67 MnO 3 [2,5,6] demonstrates that the long-range Coulomb interaction might be the main driving force of the CO state, and indeed, some theoretical calculations [7,8] support the Coulombic model. However, if CO state was mainly due to long-range Coulomb interaction, the z-axis stacking of charges [9] and the observed "bi-stripe" CO state [10] which are both energetically penalized by the nearest-neighbor Coulomb repulsion V NN , therefore, can not be fully understood based on the Coulombic model. This shows that other ingredients, especially the electron-lattice interaction with the JT effect, are needed to understand the formation of CO state. The theoretical calculations in Refs. [3,4,[11][12][13][14][15][16] have shown that the JT effect not only stabilizes the CO state, but also strongly affects the magnetic structures. The relative importance of the long-range Coulomb interaction or the electron-lattice interaction with

We report the Ti-doping effects on the total magnetization of perovskite SmFe1−xTixO3 samples with x = 0, 0.1, 0.2, and 0.3. X-ray diffraction and Raman spectroscopy studies indicate that with the increase of Ti doping concentration, the lattice parameter b decreases and the oxygen octahedron is compressed along b axis. Such lattice distortion is also reflected by the changes of antisymmetric stretching mode and symmetric stretching mode of the oxygen octahedron through Raman spectra measurement. An enhancement of the interaction between Sm-4f and Fe-3d electrons is observed due to Ti-doping. This strong interplay between Sm-4f and Fe-3d electrons weakens the total magnetization and considerably suppresses the weak ferromagnetism of Fe sublattice starting from 260 K.