Relaxation time, single-domain magnetic

Thermofluctuational behavior of the magnetic moment in a magnetically anisotropic particle acquires new features in comparison with the isotropic case and, accordingly, extends the set of relaxation times. Let us consider a single-domain particle with the easy-axis anisotropy defined by... 

In a single-domain particle of a-Fe203 the magnetization vector is held in the c-plane perpendicular to the c-axis by the magnetocrystalline field. Mossbauer studies use the 57Fe nucleus as the "observer to record when the relaxation time t becomes shorter than the period for precession of the nuclear spin about the direction of the effective field. Substitution into the equation for the Larmor frequency, or observer relaxation time, with an expression for the frequency factor proportional to the specific volume and anisotropy constant of the oxide gave (26, 27) the relationship ... 

Cregg PJ, Crothers DSF, Wickstead AW (1994) An approximate formula for the relaxation time of a single domain ferromagnetic particle with nniaxial anisotropy and collinear field. J Appl Phys 76 4900-4902 Dang MZ, Rancourt DG (1996) Simnltaneons magnetic and chemical order-disorder phenomena in FesNi, FeNi, and FeNij. Phys Rev B 53 2291-2301... 

Using this method it is possible to calculate the longest relaxation time of M for a single domain ferromagnetic particle with large uniaxial anisotropy. It is also possible to calculate the longest relaxation time when the particle is in the presence of an external magnetic field applied... 

The relaxation time T (o-, ) for the magnetization of a single domain ferromagnetic particle with uniaxial anisotropy in the presence of an external field from T = Mp and Eq. (3.129) is... 

Ti) and spin-spin (T2) relaxation time constants. Fourier transformation of the time domain data produces a frequency spectrum where the amplitude at each frequency is a measure of the number of nuclei in the corresponding region in space. In magnetic resonance imaging a multivariate slice for one pulse sequence is used if spatial resolution is most important. A full NMR spectrum can be produced for a single point inside the material if the spectral aspect is most important. 

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