无序化对有序铁铝金属间化合物磁性的影响

在平衡态时，化学计量比成份Fe3Al具有DO3超结构，并表现出铁磁性，平均每个Fe原子的磁矩是1．7μB，而具有B2超结构的FeAl却是无磁的。利用快速凝固、冷加工处理、溅射和机械合金化等非平衡加工技术可以使DO3-Fe3A1和B2-FeAl等有序铁铝金属间化合物相无序化。本文利用固体与分子经验电子理论（EET）和Jaccarino—Walker模型对铁铝金属间化合物的磁性进行了计算，研究了无序化对Fe-Al有序相磁性的影响。结果表明：完全无序的Fe15Al25和Fe50Al50，每个Fe原子的平均磁矩分别是2．01μB、1．41μB，铁铝金属间化合物的磁性可以通过无序化提高。     

Fine-grained NdFeB magnets prepared by low temperature pre-sintering and subsequent hot pressing

Fine-grained Nd10.79Pr2.8Al0.4B7.72Fe78.29magnets were prepared by low temperature pre-sintering and subsequent hot pressing.The grain size of the magnets is just about 1–3μm because the low sintering temperature results in no grain growth.The orientation degree,microstructure,and magnetic properties were studied.Some grains’easy axes deviate from the orientation direction,possibly due to grain rotation during the hot pressing.By subsequent annealing,the magnetic properties were significantly enhanced.Especially,the squareness of the demagnetization curve was improved greatly.The enhancement of coercivity by annealing can be explained by an improvement of both grain boundaries and magnetic isolation,which decouples the exchange interaction between neighboring grains.     

Al-Fe3O4体系在机械力化学过程中的物理化学变化

将纳米磁性粒子嵌入到绝缘基体中形成的磁性复合粒子,在许多方面具有重要意义。本文利用A l-Fe3O4通过机械力化学方法原位生成Fe/A l2O3磁性复合粒子。通过对球磨不同时间的A l-Fe3O4粉末进行X射线衍射(XRD)和示差扫描量热(DSC)分析,结果表明A l-Fe3O4混合粉末通过机械力化学方法可获得Fe/A l2O3复合粒子。同时较为详细地研究了上述体系在机械力化学过程中的物理化学变化,并提出了机械力化学过程中A l-Fe3O4体系固相反应的方式。