Critical behavior and magnetic-entropy change of orthorhombic La0.7Ca0.2Sr0.1MnO3 J. Appl. Phys. 112, 093906 (2012) Reversible solid-state hydrogen-pump driven by magnetostructural transformation in the prototype system La(Fe,Si)13Hy J. Appl. Phys. 112, 083918 (2012) Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3 J. Appl. Phys. 112, 083917 (2012) On the estimation of the magnetocaloric effect by means of microwave technique AIP Advances 2, 042120 (2012) Magnetocaloric properties of La0.7Ca0.3Mn16O3 and La0.7Ca0.3Mn18O3 manganites and their "sandwich"A systematic study of the conventional and inverse magnetocaloric effects and critical behaviors in Ni 50 Mn 50Àx Sn x (x ¼ 13 and 14) alloy ribbons has been performed. We show that although the magnetic entropy change around the second-order ferromagnetic-paramagnetic (FM-PM) transition (DS m % À4 J/kg K) in the austenitic phase is about five times smaller than that around the first-order martensitic-austenitic (M-A) transformation (DS m % 22 J/kg K), the refrigerant capacity (RC) -an important figure of merit -is about two times larger for the former case (RC % 160 J/kg) than for the latter case (RC % 75 J/kg). This finding points to an important fact that to assess the usefulness of a magnetocaloric material, one should not only consider DS m but also must evaluate both DS m and RC. Our critical analysis near the second-order FM-PM transition reveals that Sn addition tends to drive the system, in the austenitic FM phase, from the short-range (x ¼ 13) to long-range (x ¼ 14) FM order.

Polycrystalline BaTi1−xFexO3 ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi1−xFexO3 samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02–0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra.

Though ZnO is known as a diamagnetic material, recent studies have revealed that its nanostructures can be ferromagnetic (FM). The FM origin has been ascribed to intrinsic defects. This work shines light on an alternate method based on mechanical milling to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic ZnO powders. Our idea is motivated by the fact that mechanical milling introduces more defects to a ground material. We point out that the FM order increases with increasing the density of defects in ZnO NPs. The experimental results obtained from analyzing X-ray absorption, electron spin resonance, and Raman scattering spectra demonstrate that the ferromagnetism in ZnO NPs is due to intrinsic defects mainly related to oxygen and zinc vacancies. Among these, zinc vacancies play a decisive role in introducing a high FM order in ZnO NPs.

Our work studies the influences of the Mn doping on structural characterization and optical and magnetic properties of BaTi1−xMnxO3 (x = 0.0–0.12) prepared by conventional solid-state reaction. Detailed analyses of XRD patterns and Raman scattering spectra indicate an incorporation of Mn dopants into the Ti sites of BaTiO3 host lattices, and the tetragonal-hexagonal transformation taking place at a threshold concentration of xc ≈ 0.01. An increase of Mn-doping content in BaTi1-xMnxO3 introduces more electronic levels associated with lattice defects and Mn ions to the forbidden gap and thus reduces luminescent intensity in the visible region. Magnetic data recorded at room temperature reveal that all the samples exhibit ferromagnetic order, and there is a phase separation in magnetism as varying x values. Particularly, the samples with x = 0.5–0.7 have a coexistence of two ferromagnetic phases with different coercivities, which are associated with tetragonal and hexagonal Mn-doped BaTiO3 structures. The nature of ferromagnetism is explained by means of the results of structural and optical analyses, where Mn3+ and Mn4+ ions play a crucial role.