Demagnetization field effects

Agreement between theory and experiment becomes quantitative, if the demagnetizing field effects are also taken into account. This leads to values of the anisotropy field, HK=29 G and the demagnetizing field, Hdem=-39 G. The nonlinear dependence of the resonance field on the resonance frequency disappears... 

This simple discussion of the demagnetizing field effects in hard nanostructures show that the usual corrections should not be applied without careful analysis of the system behavior. In particular, it may be suggested that the impossibility to apply the 1 IN corrections found in several FePt hard... 

Demagnetizing Field Effects of Magnetic Dots Array... 

Prof. Levitt uses the term demagnetization field effect (as will we) but terms such as bulk nuclear-paramagnetic-susceptibility-induced transients, dipolar field, or bulk susceptibility effects have also been used. 

Figure 5 Cold probe demagnetization field effects. (A) shows the lock responses of a 90/10 H2O/D2O sample while (B) shows the lock of a 98% D2O sample. The marked intervals correlate to (i) equilibrium unlocked as a control, (ii) equilibrium with lock circuit active, (iii) locked while repeatedly pulsing with a 2.5 s 90 Hz presaturation pulse and a 4 s recycle time, and (iv) the same repeating presaturation sequence as shown in (iii) but with an inactive lock circuit. Results are from an 800 MHz spectrometer with a 5 mm HCN cryogenically cooled probe.

Demagnetizing field effects and hysteresis. Special attration must be paid to the distinction between internal and external (applied) magnetic field, in particular as far as a first-order transition is concerned. For an ellipsoidal sample, it is well known that the magnetization is uniform as a function of the applied field //ext) but actually the magnetic ions experience an effective internal field, H, instead of //ext ... 

Paramagnetic case. In this case, M = x H (where x i the effective susceptibility including demagnetization-field effects), so that... 

The precessional motion can be maintained by a suitable radio frequency field superimposed on the steady field. For example, in Fig. 9.38(b), when a steady field Hz is applied along the z axis and a radiofrequency field //,., is applied in the x-y plane and rotates in the same sense and at the same frequency as the precession, resonance occurs. Gyromagnetic resonance as outlined above is in principle the same as ferrimagnetic resonance referred to earlier (Section 9.3.1), except that in the former case the material is magnetically saturated by a strong applied field. In practice the steady field, which determines the Larmor frequency, is made up of the externally applied field, the demagnetizing field and the anisotropy field, and is termed the effective field He. Figure 9.39 shows the He values at which resonance occurs in some of the important communications and radar frequency bands. 

Eq. (2), together with assumptions about the grain shape (typically cylinders with constant height 8), the demagnetization field and the actual Eb/IcbT requirement, can be used to estimate the minimal thermally stable grain size Dp Before calculating Dp for a variety of media materials, we first consider the effect of physical grain dispersions on the Ej kRT requirement. 

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