Youfang Lai

One step preparation of pure 𝝉-MnAl phase with high magnetization using strip casting method

Ferromagnetic phase of Mn-Al exhibits great potential in the rare-earth free permanent magnetic materials due to its high magnetocrystalline anisotropy, high magnetization, high Curie temperature and low cost. In this work, the strip casting technique was applied to prepare MnAl magnetic phase. X-ray diffraction and energy dispersive X-ray analyses indicate that the as-prepared Mn54Al46 strip sample consists of pure τ-MnAl magnetic phase. It is found that the composition of Mn54Al46 is suitable to prepare τ-MnAl phase during the strip casting process. The Mn54Al46 strip sample synthesized through the strip casting exhibits a fairly high magnetization of 114 emu/g under a field of 5 T, while the coercivity of iHc = 2.8 kOe, magnetization of M5T = 63.9 emu/g at room temperature can be obtained for Mn54Al46 powder sample. This preparation method can produce a large amount of τ-phase MnAl alloy and promote mass industrialized production.

The magnetic properties of NdMn x Cr2−x Si2C (0 < x < 2)

Carbon was successfully introduced into NdMn x Cr2−x Si2 serial compounds as an interstitial atom. The compounds with x ≤ 0.5 keep a CeMg2Si2-type structure while the structure changes slowly with increasing manganese content. Finally, a new superstructure was found and determined for x around 1.7. All the compounds for x = 1.1, 1.3, 1.5 and 1.7 have two magnetic phase transition temperatures around 43 and 314 K. What is more, a giant magnetocaloric effect has been observed around the lower phase transition temperature, T R ~ 51 K, in NdMn1.7Cr0.3Si2C. The maximum values of the magnetic entropy change −ΔS M for the field change of 2 T and 5 T are 14.9 J kg−1 K−1 and 26.0 J kg−1 K−1, which means the interstitial atom effect enhanced the MCE values for 85% and 63% compared to NdMn1.7Cr0.3Si2, respectively. NdMn1.7Cr0.3Si2C with first order magnetic transition but low hysteresis losses (thermal < ~0.58 K; magnetic field < ~0.12 T) can be a candidate for magnetic refrigerator applications in the temperature region near 50 K. Besides, two field-induced magnetic phase transitions were found in NdMn1.7Cr0.3Si2C among the temperature range from 53 to 60 K, and a linear relation between the phase transition field and temperature was found and analyzed.