Low-temperature coercivity of Mo2NiB2-type Tb2Co2Ga and Tb2Co2Al-based solid solutions

Highlights: • Tb₂Co₂Ga and Tb₂Co₂Al-based solutions show high-temperature ferromagnetic ordering. • This HT ferromagnetic ordering corresponds to the negative ΔS_m and soft magnet properties. • They exhibits low-temperature field sensitive transformation of magnetic ordering. • This LT transformation is followed positive ΔS_m and permanent magnet properties. • Tb₂Co₂Ga is giant permanent magnet with H_coer of 48 kOe and (BH)_max of 1068 kJ/m³ at 2 K. -- Abstract: The magnetic ordering of polycrystalline Mo₂NiB₂-type Tb₂Co₂Ga and Tb₂Co₂Al-based Sm_2-xTb_xCo₂Al, Tb₂Co₂Al_1-xGa_x and Tb₂Co_1.8{Ni, Cu}_0.2Al solid solutions has been established using bulk magnetic measurements. These compounds undergo a high-temperature ferromagnetic ordering and field sensitive transformation of magnetic ordering at low temperatures. The high-temperature ferromagnetic ordering is followed via negative magnetic entropy change and soft magnet properties, whereas low-temperature transformation of magnetic ordering indicates positive magnetic entropy change and excellent permanent magnet properties.