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Small-angle neutron scattering (SANS) has been used to measure the ferromagnetic correlation length in La0.67Ca0.33MnO3. This is of interest in these materials because the transport mechanism responsible for colossal magnetoresistivity involves valence fluctuation on the Mn sites, and thus, spin fluctuations. There should then be a direct relationship between the magnetoresistivity and the spin–fluctuation correlation length. The magnetic SANS was determined by substracting 15 K data from the data at and above TC (250 K). When the quasistatic approximation is valid, the magnetic SANS measures the static equal-time two-spin correlation function. In an ideal isotropic ferromagnet, the fluctuations that drive the phase transition are the transverse (below TC) spin waves, which have a divergent correlation length at and below TC. Our measurements show that the magnetic scattering function for temperatures above TC is approximately Lorentzian. However, the extracted correlation length is anomalously small, starting at about 6 Å at 400 K and increasing only to about 11 Å at the nominal TC=250 K. The correlation length continues to increase below TC to about 14 Å at 225 K. Inelastic scattering measurements suggest that there are significant diffusive fluctuations near TC in addition to the spin waves. We are performing SANS measurements in a magnetic field to try to separate the correlation lengths of these two types of fluctuations.

Materials with excellent magnetocaloric properties are a key factor for the application of magnetic refrigeration technology. In this work, an amorphous ribbon of quaternary Gd₄₅Ni₃₀Al₁₅Co₁₀ alloy is designed and prepared, and the magnetocaloric properties of the alloy are systematically studied. The introduction of Co can improve the thermal stability of the amorphous structure. The Curie temperature and effective magnetic moment of Gd₄₅Ni₃₀Al₁₅Co₁₀ amorphous ribbon are 80 K and 7.21 μ_B, respectively. At 10 K temperature, the saturation magnetization and the coercivity of the alloy reach 173 A·m²·kg^–1 and 0.8 kA·m^–1, respectively, which indicates excellent soft magnetic properties. At 5 T magnetic field, the peak value of magnetic entropy change and relative cooling capacity of Gd₄₅Ni₃₀Al₁₅Co₁₀ amorphous alloy are as high as 10.2 J·kg^–1·K^–1 and 918 J·kg^–1 respectively. The amorphous alloy has typical secondary magnetic phase transition characteristics, and the magnetic refrigeration can be realized in a wide temperature range. The Gd atomic content is less than 50% with low cost, which means that the alloy is an ideal magnetic refrigeration material.