Initial magnetic permeability

In effect of loads acting in the scope of elastic deformations (proportional) in polycristalline bodies, changes in distances between atomic surfaces of the net are observed, which change the initial magnetic permeability. 

Cedillo, E., Ocampo, J., Rivera, V. Valenzuela, R. (1980). An apparatus for the measurement of initial magnetic permeability as a function of temperature. Journal of Physics F Scientific Instruments, 13, 383-6. 

Fillers (phr) Saturation Magnetization (emujg) Experimental Theoretical A% Initial Magnetic Permeability Remnant Magnetization (emujg) Coercive Field (Oe)... 

B = 0). The initial slope of the B-H curve is called the initial magnetic permeability and... 

Thus, we see the initial connection between optical properties and the electrical and magnetic properties from the two previous sections. Substimtion of Eqs. (6.78) and (6.79) into (6.77) shows that the refractive index can be expressed in terms of the relative electric permittivity (dielectric constant), (cf. Table 6.5), and relative magnetic permeability of the medium, (1 - - x) [cf. Eq. (6.63)], where x is the magnetic susceptibility ... 

L = FID liquid signal intensity Mg = initial magnetization Ps,y R, A) = average displacement propagator P = permeability q = diffusion wavevector defined as 2k) yG5 R = distance diffused by a spin S= amplitude of solid component in FID S = chemical shift 5 = FID solid signal intensity S q, A) = stimulated echo amplitude q = pulse separation time T2 = transverse relaxation time VI/= width of lamellar regions A = diffusion time Y= gyromagnetic ratio. 

The thus obtained high-density Mn-Zn ferrite was investigated in detail from the view of physical and mechanical properties, that is, the relationships between the composition of metals (a,) ) and <5 the magnetic properties such as temperature and frequency dependence of initial permeability, magnetic hysteresis loss and disaccommodation and the mechanical properties such as modulus of elasticity, hardness, strength, and workability. Figures 3.13(a) and (b) show the optical micrographs of the samples prepared by the processes depicted in Fig. 3.12(a) and (b), respectively. The density of the sample shown in Fig. 3.13(a) reached up to 99.8 per cent of the theoretical value, whereas the sample shown in Fig. 3.13(b) which was prepared without a densification process, has many voids. 

A quantitative study of the process indicates that, as the field intensity H increases, the magnetic induction B also increases in a manner characteristic of the substance, This is conveniently represented by a graph, which is called the magnetization curve. See Fig. 1. Its initial slope is the initial permeability (/Xo). If H is carried to some maximum value H , and then reduced (to - //,), R follows the dotted hysteresis curve. B does not fall off as it was built up (solid line) the residual induction B, is... 

The capsules with a defined shell (so-called hollow multilayered polyelectrolyte capsules) are free-standing LbL films with a peculiar advantage - the ability to uptake the material inside the capsule, in other words to encapsulate it and to control its release by changing the LbL film permeability properties. Macromolecules like proteins have been successfully loaded into polyelectrolyte LbL capsules through pH-controlled and water/ethanol mixture-controlled methods [118, 119], Alternative stimuli could be applied, e.g., a magnetic field [120], This approach consists of destabilization of the LbL membrane, which then becomes more permeable. The capsule is loaded with molecules of interest under destabilized conditions and then the conditions are changed back to the initial ones (under which the LbL shell is stable). 

Figure 1. Saturation magnetization and initial permeability of various soft magnetic materials. The open squares and circles denote FINEMET [1, 6] and NANOPERM [8, 25], respectively.

It is worth mentioning here that a compound-free bcc-Fe nanostructure with grain sizes smaller than L0 can be obtained even in a binary Fe Zrg alloy [3, 60] although the initial permeability of nanocrystalline Fe92Zr8 (2 x 103 at 1 kHz) is similar to that of magnetically soft Fe-Si steels. Weak... 

Figure 11. Compositional dependences of initial permeability (pc at 1 kHz) and saturation magnetization (Js) for nanocrystalline (a) Fe-Zr-B [3] and (b) Fe-Zr-B-Cu [34] alloys.

An important property of soft magnetic materials is the initial permeability. Its dependence on microstructure can be understood in terms of the Globus model. A calculation of the (relative) initial permeability (Globus, Duplex Guyot, 1971) leads to the following expression ... 

This group of soft-ferrite applications is based on their ability to transform ac signals of small amplitude into substantially large variations of magnetic flux. The fact that at low fields the initial permeability is a linear function of the field explains the name these devices are also known as small-signal applications. There are other materials, such as metallic alloys (see Chapter 6), which possess permeability values considerably higher than the typical values of ferrites however, as frequency increases, conductivity losses prevent efficient use of metallic materials. 

The basic magnetic properties expected in soft magnets are high initial and maximum permeabilities, p-, and r,., and low coercivity, (lower than 10 A/m). In many applications, soft magnets are subjected to ac fields their frequency response and, particularly, their ac losses are therefore important. 

In the Ni-Fe system at room temperature, the a phase extends from 0 to 7% Ni, then a. Fy mixtures from 7 to 50% Ni, and the y phase from 50 to 100% Ni. y-Phase alloys in the Ni-Fe system, known as Permalloys, exhibit a wide variety of magnetic properties, which may be controlled precisely by means of well-established technologies. Initial permeabilities up to 10 in an extremely wide temperature range, as well as coercive fields between 0.16 and 800 A/m, can be obtained (Chin Wemick, 1980). Induced anisotropy of 65-85% Ni alloys can be drastically varied by field annealing and mechanical deformation (slip-induced anisotropy) an order-disorder transformation occurs for Ni3Fe finally, preferential orientation can be induced in 50%Ni-50%Fe. 

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