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The double-perovskite Nd2CoMnO6 (NCMO) thin films were epitaxially grown on LaAlO3 and SrTiO3 substrates with different orientations by the polymer-assisted deposition technique. A well crystallization quality of the films is confirmed by x-ray diffraction. The magnetism measurement suggests that all the films have a single ferromagnetic (FM) transition, but its substrate-orientational dependence is different from those in normal perovskite ABO3. By the analysis of the valence states of cations combining with the single FM transition, we suggest that the ionization degree of Co and Mn can be stimulated under both tensile and compressive strain, which can weaken the magnetic interaction. Thus, there are two aspects that competitively affect the magnetism [M(T) and Tc] of the NCMO film, i.e., the variation of oxygen octahedron similar to that in the normal perovskite ABO3 film and the degree of Co/Mn ionization, without changing the order of Co–O–Mn chain arrangement, resulting in the different orientation-dependent magnetism in NCMO films from that normally observed in ABO3 films. Our results give a systematic understanding of the substrate-induced-strain influence on the magnetic interaction in NCMO thin films and widen its practical application.

The R2CoMnO6 (R = Pr, Nd, Sm) thin films on (001) LaAlO3 substrates were fabricated successfully by a simple polymer assisted deposition method, confirming by atomic force microscopy, X-ray diffraction, and Raman spectroscopy. The study on the magnetic properties indicates that all the films are B-site ordering and show a single ferromagnetic transition at Curie temperature (Tc) with decreasing temperature. Meanwhile, an anomalous phonon softening related to the spin-phonon coupling is observed at around Tc in all the temperature-dependent Raman spectra. With the decreases of R-site ionic radius (rR) and/or the in-plane biaxial compressive strain, both the turning point TR of the temperature-dependent Δω(T) and Curie temperature Tc decrease, revealing the existence of spin-phonon coupling and its intensity in the decreasing order of Pr2CoMnO6 > Nd2CoMnO6 > Sm2CoMnO6 accompanied with the Co-O-Mn bond angle decreasing and the Co(Mn)-O bond length elongating. It is suggested that the existence of the biaxial...

The epitaxial NdNi1-xCoxO3 (0 ≤ x ≤ 0.10) thin films on (001) LaAlO3 and (001) SrTiO3 substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO3 thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (TMI) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With t...

Transport properties of polycrystalline La1−xCaxCoO3 (0.10 ≤ x ≤ 0.25) are systemically studied in this work. Three types of magnetoresistance (MR) effects are found in the Ca-doped cobaltites. Two negative MRs appear around high-temperature ferromagnetic transition and at low temperatures, which correspond to the conventional MR due to the field-induced suppression of spin-disorder scattering and the intergranular giant-MR due to spin-dependent transport between the ferromagnetic clusters, respectively. More interestingly, another exotic positive MR emerges at intermediate temperature region, which had not been previously reported in Sr- and Ba-doped cobaltites. It is found that this positive MR is associated with an abnormally magnetic transition and increases with the increase of x. For x = 0.25, the MR at low temperatures is dominated by the positive one, which is isotropic and nearly linear with the magnetic field. The possible origin of the positive MR in the Ca-doped cobaltites is discussed.

The ceramic Pr2CoMnO6 of double perovskite structure is prepared by a solid-state reaction and the magnetic properties, phonon behaviors are studied in detail. Two ferromagnetic transitions at TC1 ∼ 172 K and TC2 ∼ 140 K are observed in the temperature-dependent magnetization curves, respectively. Furthermore, a detail analysis on the magnetic susceptibility reveals that a short-range ferromagnetic clustered state exists above TC1, which can be well described as the Griffiths phase with a well-defined Griffiths temperature TG ∼ 210 K. The presence of the B-site antisite defects is considered to contribute to the observed Griffiths singularity. Temperature-dependent Raman scattering experiment reveals an obvious softening of the phonon mode involving stretching vibrations of the (Co/Mn)O6 octahedra in FM temperature regions, indicating a close correlation between magnetism and lattice in Pr2CoMnO6. On the other hand, it is found that the phonon softening extends up to TG, which further confirms the preform...

The structure and magnetic properties of orthorhombic DyMnO3 nanoparticles with different particle sizes are investigated in this paper. With decreasing particle size, all the lattice parameters a, b, and c gradually decrease, whereas the orthorhombic distortion increases. Magnetic measurements reveal that the antiferromagnetic interaction of Mn ions is weakened due to the decrease in Mn-O-Mn bond angle. Above a critical field H*, DyMnO3 undergoes a field-induced metamagnetic transition at 4 K, which is related to the spin reversal of Dy moments. The critical field H* increases monotonically with size reduction, indicating an enhancement of the antiferromagnetic interaction of Dy ions due to the decreased distance between rare earth ions. The magnetization at 4 K and 5 T, i.e., M(4 K, 5 T) shows a non-monotonic variation with particle size d, i.e., M(4 K, 5 T) initially increases with size reduction but decreases again for d

The structure and magnetic properties of La2NiMnO6 nanoparticles with sizes ranging from about 16 to 66 nm synthesized by a sol-gel method have been investigated. The magnetic measurements reveal that the rates of disordered phases increase as particle size decreases, which can be deduced from the changes of Curie temperature and the occurrence of glasslike behaviors, and the similar saturation magnetization was obtained at 4 K. While the particle size becomes smaller, two broad peaks of Raman spectrum at around 535 and 670 cm−1, which are assigned to antisymmetric stretching mode and symmetric stretching mode, move to higher and lower frequencies than the corresponding modes of the bulk compound, respectively. The two peaks also become broader, while the intensity becomes relatively weaker with the decrease in nanoparticle size. All results support that the trend of Mn4++Ni2+→Mn3++Ni3+ bring locally cooperative Jahn–Teller deformation and charge disproportion, and demonstrate that the nanometer effect is a crucial factor to influence the properties of La2NiMnO6.

The magnetic properties of the double perovskite La2NiMnO6 polycrystalline sample have been investigated by magnetometry and electron spin resonance. The magnetization curve shows a paramagnetic-ferromagnetic transition at TC∼280K. However, the electron spin resonance spectra reveal that a pure paramagnetic regime only exists above T*∼390K in which the behaviors of the spectra can be well described by the small polaron hopping model. Between TC and T*, a short-range magnetic ordering appears which maybe derives from the correlation of those magnetic polarons. The possible relationship between those polarons and the observed multifunctions in La2NiMnO6 is briefly discussed.

A series of polycrystalline bulk samples of Mg1−2x(AgAl)xB2 (0.0%⩽x⩽1.0%) has been synthesized by a solid state reaction method. The structure, Raman spectrum, and superconducting properties have been investigated by x-ray diffraction, Raman spectroscopy, and low-temperature resistivity measurements. It is found that the Ag, Al double doping causes the expansion of crystal lattice along the a- and c-axis orientations due to the substitution inducing ionic size variation. A redshift of peak position is observed in Raman spectra, which is ascribed to the crystal cell volume change inducing the variation of the phonon frequency. The superconducting transition temperature (Tc) is degressive with the doping level (x) increase. By the Ag and Al double doping, the hole concentration is kept to be unchanged in MgB2, which eliminates the effects of the charge carrier concentration change and band filling on Tc. It is suggested that the reason of the Tc suppression caused by the double doping is the co-operating re...