THE STRUCTURE AND PROPERTIES OF L1(0), ORDERED FERROMAGNETS - CO-PT, FE-PT, FE-PD AND MN-AL
THE STRUCTURE AND PROPERTIES OF L1(0), ORDERED FERROMAGNETS - CO-PT, FE-PT, FE-PD AND MN-AL
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DOI：
10.1016/0956-716x(94)90182-1
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发表时间：
1994-03-15
期刊：
影响因子：
--
通讯作者：
SOFFA, WA
中科院分区：
文献类型：
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作者：
ZHANG, B;SOFFA, WA
从结构-性质的观点来看，一类有趣的铁磁体源自有序系统中L10超结构的形成，例如Co-Pt、Fe-Pt、Fe-Pd族和MnAl基合金。在Co-Pt族中，图1所示的L10相源自Al（fcc）.-，L10有序化转变通过成核和生长过程发生（1），而在MnAl型合金中，L10相源于有序（B 19）正交相内的剪切或置换转变（2）。在这两种情况下，得到的L10（CuAl型）超结构都表现出强的单轴磁晶各向异性，其K值为-107-10sergs/cm3（3）。MnAl基材料中的铁磁（x）相是亚稳态的，并且x相的稳定性是基于该系统的永磁体的热机械加工和热处理中的主要关注点。添加碳作为铁磁X相的稳定剂非常有效，防止分解成平衡Y 2和Y 4相。因此，商用永磁体基本上基于Mn-Al-C三元体系（4）。重要的是，在Co-Pt、Fe-Pt、Fe-Pd和Mn-Al-C永磁体材料中形成的具有”易”c轴的单轴L10相继承了主要由高密度的扩展平面缺陷（即，孪晶、APB和堆垛层错）组成的缺陷结构（5，6）。微孪晶调制磁化的易磁化方向，并且晶体学上施加跨孪晶平面的自旋跃迁。在Co-pi族中，变换孪晶是沿着{110}平面沿着共轭的，而在Mn-Al-C铁磁体中，孪晶是沿着沿着x相的{111}平面，使用常规的fcc参考单元（5，6，7）。已经表明，在CoPt型合金（10）中形成的磁调制结构中，从一个微孪晶到另一个微孪晶，易磁化轴旋转90 °。APB代表MnAl基合金中的一种特殊磁性情况，因为断层附近原子有序的扰动改变了Mn原子的最近邻距离，产生了局部反铁磁耦合（8，9）。这导致APB在磁化和退磁期间主要用作反向畴的成核中心。在Co-Pt、Fe-Pt和Fe-Pd合金中发展的APB是由有序转变期间无序母相中生长的Llo颗粒的撞击引起的，并且这些APB似乎主要用作这些材料的微孪晶集合特征内的迁移畴壁的钉扎中心（10）。然而，在这两类L10铁磁体中，平面缺陷与磁化和退磁过程的相互作用是理解材料结构与磁性之间关系的核心。Fe-Pd和Mn-Al-C永磁材料。此外，一些最近的洛伦兹显微镜研究的独特的域配置出现在多孪晶的Fe-Pt和Fe-Pd合金将被提交这些有序的铁磁体中的磁性机制。虽然Co-Pt合金族永远不会成为大体积永磁材料，但它们在薄膜应用方面仍具有巨大的潜力，
An interesting class of ferromagnets from the structure-properties point of view derives from the formation of the L1 o superstructure in ordering systems such as the Co-Pt, Fe-Pt, Fe-Pd family and the MnAl-base alloys. In the Co-Pt family the L10 phase shown in Figure 1 derives from an Al (fcc).-, L10 ordering transformation which occurs via a nucleation and growth process (1) whereas in the MnAl-type alloys the L10 phase stems from a shear or displacive transformation within an ordered (B 19) orthorhombic phase (2). In both instances the resultant L10 (CuAultype) superstructure exhibits a strong uniaxial magnetocrystalline anisotropy with K~-107-10 s ergs/cm 3 (3). The ferromagnetic (x) phase in the MnAl-base materials is metastable and the stability of the x-phase is a major concern in the thermomechanical processing and heat treatment of permanent magnets based on this system. The addition of carbon is very effective as a stabilizer of the ferromagnetic x phase against decomposition to the equilibrium Y2 and [~ phases. Thus, commercial permanent magnets are essentially based on the Mn-AI-C ternary system (4). Importantly, the uniaxial L10 phase with an" easy" c-axis forming in the Co-Pt, Fe-Pt, Fe-Pd, and Mn-A1-C permanent magnet materials inherits a defect structure comprised primarily of a high density of extended planar faults, viz. twins, APB's, and stacking faults (5, 6). The microtwins modulate the easy direction of magnetization and crystallographicaUy impose a spin transition across the twin plane. In the Co-pi family the transformation twins are conjugated along the {110} planes whereas in the Mn-A1-C ferromagnets the twins are along the {111} planes of the x-phase using a conventional fcc reference cell (5, 6, 7). It has been shown that the easy axis rotates by 90 in going from one microtwin to another in the magnetically modulated structure which forms in the CoPt-type alloys (10). The APB's represent a special situation magnetically in the MnAl-base alloys because the perturbation of the atomic order in the vicinity of the fault alters the nearest-neighbor distances of the Mn atoms producing a local antiferromagnetic coupling (8, 9). This causes the APB's to act primarily as nucleation centers for reverse domains during magnetization and demagnetization. The APB's which develop in Co-Pt, Fe-Pt, and Fe-Pd alloys result from the impingement of the growing Llo particles within the disordered parent phase during the ordering transformation and these APB's appear to act primarily as pinning centers for migrating domain walls within the microtwin ensembles characteristic of these materials (10). However, in both classes of L 10 ferromagnets, the interaction of the planar faults with the processes of magnetization and demagnetization is at the core of understanding the relationship between material structure and magnetic properties.In this short paper a simple framework based on domain wall pinning is discussed to provide a semiquantitative basis for understanding the relationship between structure and properties in the Co-Pt, Fe-Pt, Fe-Pd, and Mn-A1-C permanent magnet materials. In addition, some recent Lorentz microscopy studies of the unique domain configurations which emerge in the polytwinned Fe-Pt and Fe-Pd alloys will be presented which relate to the mechanism of coercivity in these ordered ferromagnets. Although the Co-Pt family of alloys will never become large volume permanent magnet materials they still have great potential for thin film applications including perhaps