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Bulk CoCr2O4 undergoes a transition from paramagnetic to long-range ferrimagnetic phase at Tc (94 K) to a long-range and/or short-range spiral order at Ts ( \sim 24 K), and finally shows a lock-in-transition below 15 K. The spiral component induces an electric polarization and also a spontaneous magnetization for which it is said to be multiferroic. Reducing the size of a CoCr2O4 multiferroic material to \sim 50 nm by a coprecipitation method, we obtain a pure cubic phase with space group, Fd3m and lattice parameter (8.334 ± 0.003 °A). A rich sequence of magnetic transitions are examined by measuring temperature and field-dependent magnetization and diffused neutron scattering (DNS) using polarized neutron at different temperatures. While paramagnetic to ferrimagnetic transition is enhanced from 97 K in bulk to 99 K at 0.5 kOe field, followed by a decrease in lock-in-transition ( TL ) from 15 K in bulk to 8 K, spiral ordering temperature does not show a significant change. A strong disagreement between paramagnetic moment obtained from the fitting of \chi ^{-1}=({T}/{C})+({1}/{\chi o})-({b}/{T-\theta }) and ferrimagnetic moment obtained from the $M$ versus H$ loop taken at 2 K, nonsaturated magnetization at 50–100 kOe field, two order of magnitude higher coercivity ( H_{c} ), and splitting of ac susceptibly confirm the core–shell structure of the particles. Furthermore, a magnetic scattering analysis clearly shows that while the paramagnetic to ferrimagnetic transition is continuous, the spiral ordering is sharp, short range, and commensurate in contrast to incommensurate spiral order observed single crystal of CoCr2O4. [ABSTRACT FROM PUBLISHER]

The ferrimagnetic Mn2−xCoxSb ( $x$ = 0.15 and 0.20) alloys were prepared by arc-melting technique. The structure, magnetic, and magnetocaloric properties on these compounds were investigated. The tetragonal Cu2Sb-type structure ( $P$ 4/nmm space group) was confirmed by X-ray powder diffraction measurements at room temperature for these two alloys. The Co-introduction results in a first-order magnetic transition between the antiferromagnetic and the ferrimagnetic state. Adopting the standard and loop process method, respectively, the measurements of isothermal magnetization were performed and the magnetic entropy changes were evaluated for these alloys. [ABSTRACT FROM AUTHOR]

We report on the crystal structure and the magnetic properties of Mn5Sn3-xGax alloys with x = 0.1, 0.3, 0.5, 1.0, and 1.5, which were investigated by means of X-ray powder diffraction and magnetization measurements in fields up to 5 T in the temperature range 5 to 360 K. These alloys have in common that they exhibit a temperature-induced ferrimagnetic phase transition. The results indicate that all samples crystallize in the hexagonal Ni2 In-type structure with space group P63/mmc. The lattice parameters a and c of the Mn5Sn3-xGax decrease with increasing x, while the Curie temperature of these alloys increases with increasing x. All of the alloys exhibit a moderate magnetocaloric effect. Typical values are about 0.8 and 3 J/kgK at Tc = 282 K for x = 1.5 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively. [ABSTRACT FROM AUTHOR]