Spin moments, locked

Antiferromagnetic material - neighboring spins are locked into an antiparallel arrangement, such that the magnetic moments cancel. Manganese is antiferromagnetic. 

In this equation Tis determines the rate of polarisation transfer and hence the build up of signal, while Tip is the relaxation time of the spin-locked I-magnetisation in the rotating frame determining the time scale of the decay of the reservoir of magnetisation. The rate of transfer of the magnetisation is found to depend on the second moments (M2) of the I-S and I-I spin systems as... 

The paramagnetism of transition metal ions is mainly attributed to the magnetic moment due to the electron spin as for free radicals and triplet state molecules. The contribution due to orbital angular momentum is to a large extent quenched . In other words the orbital angular momentum is locked by the crystal field and cannot reorient in a magnetic field. 

Edelstein (1968, 1970) has adopted the Coqblin-Blandin model for cerium but with an emphasis on the effect of spin compensation. This point of view was that the decrease or loss of the magnetic moment in a-Ce and the slightly decreased moments in y- and /3-Ce (based on Lock s data) was due to the antiferromagnetic polarization of conduction electrons around the 4f virtual state. Edelstein supported this idea in part by noting an apparent T dependence of the magnetic susceptibility of mixed phase cerium samples above 13 K (Lock, 1957). This temperature dependence had been suggested by Anderson (1967) for the spin compensation contribution to the susceptibility for Kondo alloys. However, subsequent susceptibility measurements of single phase a-Ce (see... 

Where M2 is the second moment of the NMR lineshape, J the spectral density function, with (Dq the Larmor frequency, and (0i the frequency of the spin-locking field. The spectral density can be written in terms of the molecular correlation time, x, and the overall shape of the Tjp - temperature dispersion and the relatively shallow minima arc due to the correlation time distribution, although the location of the minimum is unaffected by this distribution. We have examined several models for the distribution, all of which give essentially the same results. One of the more simple is the Cole-Davidson function (75), which has also been applied to the analysis of dielectric relaxations. The relevant expression for the spectral density in this case is given by Equation 4. 

Erbium exhibits a complex magnetic behaviour, with at least four obserrable characteristic temperatures below rN = 85K, the moments order in a sinusoidal c-axis modulated (CAM) structure at rH=54K, there appears a component perpendicular to the c-axis resulting in a helicoidal structure this intermediate phase exhibits a sequence of lock-in transitions of commensurate phases (spin-slip structures) with wave vectors fm = f, 4 observed by iX-ray scattering (Gibbs et al. 1986), the... 

The concept of spin-slips or discommensurations was first introduced to explain the observed lock-in transitions in the magnetic spirals of lanthanide metals such pure Ho and Dy in terms of simple commensurate structures (fig. 127). More generally this term can be used to characterize structures which present periodic faults in a simple sequence of magnetic moments. For instance, let us consider, in an Ising chain, a sequence of 4 moments up followed by 3 moments down (this is found in some compounds). The propagation vector is In certain r ons of H-T space the propagation vector is slightly... 

Ferrimagnetic material - the spins on neighboring atoms are different, and although they are locked together in an antiparallel arrangement, the two magnetic moments do not completely cancel. 

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