We report the structural, magnetic, and magnetocaloric properties of Co 2 Cr 1−x Ti x Al (x = 0-0.5) Heusler alloys for spintronic and magnetic refrigerator applications. Room-temperature x-ray diffraction and neutron diffraction patterns along with Rietveld refinements confirm that the samples are of single phase and possess a cubic structure. Interestingly, magnetic susceptibility measurements indicate a second-order phase transition from paramagnetic to ferromagnetic where the Curie temperature (T C ) of Co 2 CrAl increases from 330 K to 445 K with Ti substitution. Neutron powder diffraction data of the x = 0 sample across the magnetic phase transition taken in a large temperature range confirm the structural stability and exclude the possibility of antiferromagnetic ordering. The saturation magnetization of the x = 0 sample is found to be 8000 emu/mol (1.45 μ B /f.u.) at 5 K, which is in good agreement with the value (1.35 ± 0.05 μ B /f.u.) obtained from the Rietveld analysis of the neutron powder diffraction pattern measured at a temperature of 4 K. By analyzing the temperature dependence of the neutron data of the x = 0 sample, we find that the change in the intensity of the most intense Bragg peak ( 220) is consistent with the magnetization behavior with temperature. Furthermore, an enhancement of change in the magnetic entropy and relative cooling power values has been observed for the x = 0.25 sample. Interestingly, the critical behavior analysis across the second-order magnetic phase transition and extracted exponents (β ≈ 0.496, γ ≈ 1.348, and δ ≈ 3.71 for the x = 0.25 sample) suggest the presence of long-range ordering, which deviates toward 3D Heisenberg-type interactions above T C , consistent with the interaction range value σ .

Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co 4−x Mn x )Nb 2 O 9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Néel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co 4 Nb 2 O 9 , the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn 4 Nb 2 O 9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co 2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn 4 Nb 2 O 9 into the noncollinear easyplane magnetic structure, which is attributed to the large easy-plane anisotropy of Co 2+ and relative small Ising-like anisotropy of Mn 2+ . The doping effects on the Néel temperature and occupancy are also discussed.