Noncollinear structure

Figure 1. Spin structures (schematic) (a) ferromagnetism, (b-c) antiferromagnetism, and (d) noncollinear structure. The shown structure of the Ll0 type the small atoms (with the large magnetization arrows) the iron-series transition-metal atoms, as compared to the bigger 4d/4f atoms. Examples of Ll0 magnets are CoPt and FePt.

A collinear (noncollinear) structure has all magnetic moments parallel (not parallel). Noncollinear and multiaxial have the same meaning. 

A field versus Gd concentration phase diagram of the Yi-jGdrCos compounds is summarized in fig. 69. The second MT of the Co sublattice is observed below 40T for 0.15<1 0.25. In this concentration range, B i) decreases linearly with increasing t. Mt> 0.25, no MT appears. However, the transition from the collinear to the noncollinear structure may occur in these compounds. For the Yi Gd/Coa compounds, the compensation composition tc where the total magnetization of the compound becomes zero, i.e., the Co sublattice magnetization equals that of the Gd sublattice, was estimated... 

Defects in ferrimagnetic structures often lead to noncollinear (canted) spin structures. For example, a diamagnetic substitution or a cation vacancy can result in magnetic frustration which leads to spin-canting such that a spin may form an angle 6c with the collinear spins in the sample [80, 81]. Similarly, the reduced number of neighbor ions at the surface can also lead to spin-canting [80-83]. 

As reported by Blanco et al. (1999), neutron diffraction patterns of powder and bulk polycrystalline samples of GdCu were obtained for both structures in the cubic CsCl type of structure, which orders antiferromagnetically at 7n 150 K, a propagation vector of ( j 0) has been found with the moments probably parallel to the c-axis (note that other noncollinear magnetic structures might give rise to the same neutron-diffraction pattern). In the orthorhombic low temperature phase (7n 45 K) the available diffraction patterns... 

Fig. 2. Structures of acousto-optic tunable filters (a) collinear and (b) noncollinear.

Antiferromagnetic sheets, but coupling between sheets gives noncollinear, canted spin structure. The two spin directions alternate in successive sheets along the c axis. Spin vectors lie in y-z plane at alternately clockwise and counterclockwise angles of 25 =fc 2° from the b axis. 

Figure 54 Noncollinear AF magnetic structures, 120° for the triangular lattice and 109° for the tetrahedral lattice. (Ref 110. Reproduced by permission of Royal Society of Chemistry)...

Mossbauer spectroscopy is also able to give local moment orientations, with respect to the crystalline lattice, or the correlations between moment orientations and local distortion axis orientations in a chemically disordered or amorphous material. This arises from the interplay between the structural (electric field gradient) hyperfine parameters and the magnetic hyperfine parameters. In this way, the spin flop Morin transition of hematite, for example, is easily detected and characterized (e.g., Dang et al. 1998). The noncollinear magnetic structures of nanoparticles can also be characterized. 

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