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The multiferroic spinel crystalline ACr2O4(A = Co, Ni) were synthesized via a traditional sol-gel reaction and characterized with respect to the structural, magnetic properties and magnetocaloric performances. The ACr2O4 oxides are confirmed to crystallize in cubic Al2MgO4-type structure with space group Fd 3 ¯ m and tetragonal CdMn2O4-type structure with I41/amdz space group for A = Co, Ni, respectively. Both ACr2O4 compounds reveal a typical second-ordered magnetic transition (SOMT) form paramagnetic to ferromagnetic (PM-FM) around its own Curie temperature TC and followed by a low temperature anomalous which is probably due to the spin glass (SG) transition behavior. The calculated peak values of magnetic entropy change (− ∆SMmax) around its own TC under the external magnetic field changes ΔH = 7 T are 1.54 and 1.19 J·kg−1 K−1 for A = Co, Ni, respectively, and the corresponding relative cooling power (RCP) is 22.2 and 22.33 J·kg−1. [ABSTRACT FROM AUTHOR]

The electromagnetic wave (EMW) absorption properties in Heusler-type ferromagnetic Ni2+xMn1−xGa alloys were systematically investigated. Significant electromagnetic absorption performance at 2.0-18.0 GHz was observed for Ni2+xMn1−xGa alloys. The values of the complex permittivity (εr) and permeability (μr), as well as the reflection loss (RL), peak frequency (fm) and bandwidth (Δf) of Ni2+xMn1−xGa can be effectively tuned by the alloy component (Ni/Mn ratio). The magnetic loss factor (tan δμ) shows pronounced multi-resonance behavior, and dielectric loss factor (tan δε) has dramatic dielectric relaxation. The RL exceeding − 10 dB corresponding to 90% absorption of incident microwave can be achieved for the Ni2MnGa in a broad frequency range of 6.3-18.0 GHz together with the thickness from 1.66 to 4.75 mm. Particularly, the maximum RL reaches − 49.1 dB at 13.3 GHz with the thickness of 2.57 mm for Ni2MnGa. The present results indicated that the ferromagnetic Ni2+xMn1−xGa alloys could be attractive candidates for broadband and high-frequency EMW absorption. [ABSTRACT FROM AUTHOR]