Magnetic field induced orientation

Firouzi, A Schaefer, DH Tolbert, SH Stucky, GD Chmelka, BE, Magnetic-Field-Induced Orientational Ordering of Alkane Lyotropic Silicate-Surfactant Liquid Crystals, Journal of the American Chemical Society 119, 9466, 1997. 

Magnetic-Field-Induced Orientation. Liquid crystals may be oriented in magnetic fields, even though they are diamagnetic, due to the anisotropy in their diamagnetic susceptibility. The advantage of magnetic fields over surface-induced orientation or electric fields is that samples are not confined to thin films. 

In addition, the external magnetic field induces magnetic moments due to electron circulation in connection with chemical bonds. The observed chemical shift for a given nucleus depends on the orientation of the molecule and of the chemical bond containing the nucleus relative to the magnetic field Bq. In a microcrystalline powder, this chemical bond will have a distribution of orientations relative to the external magnetic field, which leads to... 

Auzinsh, M., A.V. Stolyarov, M. Tamanis, and R. Ferber, Magnetic field induced alignment - orientation conversion Non-linear energv shift and predissociation in Tc2 B 1 state, J. Chem. Phys., 105 p. 37 49 (1996). 

Here nd are elastic constants. The first, is associated with a splay deformation, K2 is associated with a twist deformation and with bend (figure C2.2.11). These three elastic constants are termed the Frank elastic constants of a nematic phase. Since they control the variation of the director orientation, they influence the scattering of light by a nematic and so can be determined from light-scattering experiments. Other techniques exploit electric or magnetic field-induced transitions in well-defined geometries (Freedericksz transitions, see section (C2.2.4.1I [20, M]. 

Induced magnetic field Hp oriented in opposite direction as Hg around Hs... 

A well-known nonlinear process taking place in the liquid state of anisotropic molecules is the optical-field induced birefringence (optical Kerr effect ). This nonlinearity results from the reorientation of the molecules in the electric field of a light beam. In the isotropic phase the optical field perturbs the orientational distribution of the molecules. In the perturbed state more molecules are aligned parallel to the electric field than perpendicularly to it and as a consequence the medium becomes birefringent. On the other hand in liquid crystals the orientational distribution of the molecules is inherently anisotropic. The optical field, just as a d.c. electric or magnetic field, induces a collective rotation of the molecules. This process can be described as a reorientation of the director. 

The explanation of diamagnetism is that the application of a magnetic field induces a motion of the electrons in an atom or monatomic ion in a direction such as to give rise to a magnetic dipole with orientation opposed to the field. All substances show this diamagnetic efifect. 

Solid State Magnetic Susceptibility Measurements were conducted with a MPMS-XL 5T superconducting quantum interference device (SQUID) from Quantum Design at the University of Heidelberg in collaboration with Professor Peter Comba and recorded as a function of the apphed field (0-5 T), and at temperatures ranging from 2 to 300 K (zero field cooled method). The powdered samples were pressed into a PTEE band to avoid field-induced orientation of the... 

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