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Register a new userSmall angle neutron scattering study of the step-like magnetic transformation in Pr0.70Ca0.30MnO3
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Small angle neutron scattering (SANS) magnetic and electrical transport measurements were performed to study a single crystal of Pr0.7Ca0.3MnO3, a colossal magnetoresistive (CMR) material. While the magnetic field induced transformation of this phase separated compound consisting of an antiferromagnetic insulating phase (AFI) and a ferromagnetic insulating phase (FI), is continuous at high temperature (above 5K), at lower temperature a step like transformation is observed (around 5T at 2K). Macroscopic magnetization measurements and SANS indicate that this transformation occurs by the formation of mesoscopic ferromagnetic metallic (FM) domains in the AFI phase, and, eventually, in the FI phase. Although above 5K this transformation is continuous, below 5K a magnetization step marks the abrupt transition from a large scale FI/AFI phase separation to a large scale phase separation between AFI, FI and FM phases. Our results suggest that relaxation of elastic strains inherent to the coexistence of these different phases plays a crucial role in the mechanism of these transformations. The occurrence of magnetization steps could result from an intrinsic behavior of the AFI phase at low temperature.
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We employ magnetic small-angle neutron scattering to investigate the magnetic interactions in $(Fe_{0.7}Ni_{0.3})_{86}B_{14}$ alloy, a HiB-NANOPERM-type soft magnetic nanocrystalline material, which exhibits an ultrafine microstructure with an average grain size below 10 nm. The neutron data reveal a significant spin-misalignment scattering, which is mainly related to the jump of the longitudinal magnetization at internal particle-matrix interfaces. The field dependence of the neutron data can be well described by the micromagnetic small-angle neutron scattering theory. In particular, the theory explains the clover-leaf-type angular anisotropy observed in the purely magnetic neutron scattering cross section. The presented neutron-data analysis also provides access to the magnetic interaction parameters, such as the exchange-stiffness constant, which plays a crucial role towards the optimization of the magnetic softness of Fe-based nanocrystalline materials.
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We have evidenced by small angle neutron scattering at low temperature the coexistence of ferromagnetism (F) and antiferromagnetism (AF) in Pr0.67Ca0.33MnO3. The results are compared to those obtained in Pr0.80Ca0.20MnO3 and Pr0.63Ca0.37MnO3, which are F and AF respectively. Quantitative analysis shows that the small angle scattering is not due to a mesoscopic mixing but to a nanoscopic electronic and magnetic red cabbage structure, in which the ferromagnetic phase exists in form of thin layers in the AF matrix (stripes or 2D sheets).
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