4. Material Parameters for Domain Analysis (40 pages)
4.1 Intrinsic Material Parameters
The following magnetic material parameters are needed in domain analysis of an arbitrary material:
- The saturation magnetization Js.
- The exchange or stiffness constant A (Sect. 3.2.2).
- The gyromagnetic ratio gamma and the damping constant alphaG or alphaLL (Sect.3.2.7 C).
- The crystal and other anisotropy constants K (Sect. 3.2.3).
- The magnetostriction constants lambda (Sect. 3.2.6 B-D).
In addition, some non-magnetic material parameters, such as the elastic constants and the electrical resistivity, have to be available.
4.2 Mechanical Measurements
Fig. 4.1 Torque curves which are recorded as a function of field angle eta can be transformed into functions of the magnetization angle phi by a non-linear shearing transformation. The transformed torque curve gives direct access to the anisotropy functional of a material
4.3 Magnetic Measurements
Sketch p. 369: The setup for an optical magnetometer based on the transverse magneto-optical Kerr effect
4.4 Resonance Experiments
The basic equation for magnetic resonance, in which G is the total energy, which includes anisotropy, demagnetizing and external field energy terms
4.5 Magnetostriction Measurements
Sect. 4.5.3, p. 382: Measuring the magnetostriction constant of a thin film based on the field-dependent bending of a cantilever
4.6 Domain Methods
Fig. 4.8 The character of remanent domain patterns in perpendicular films is extremely sensitive to the direction of the previously applied saturating field relative to the hard axis of the film
4.7 Thermal Evaluation of the Exchange Constant
The exchange stiffness constant A is related to the Curie temperature Tc of ferromagnets
4.8 Theoretical Guidelines for Material Constants
Sect. 4.8.3: A connection between electronic and magnetic properties of alloys
Anisotropy and magnetostriction seem to obey similar laws as exemplified by the rule of Rassmann and Hofmann . A nickel-iron base alloy shows a maximum permeability if the cubic anisotropy and the average magnetostriction vanish simultaneously, which is obtained with the following recipe:
Take 14.5 at% Fe
Take other metals, their atomic percentage multiplied with their valence summing up to 19.5 at%
Fill up with Ni
Characteristically, the total number of electrons (percentage x valence) is the only variable in this rule.