17.1.1 Material parameters

# Material Name: This is a convenience entry for mmProbEd; inside the MIF 1.1 file it is a comment line. It relates a symbolic name (e.g., Iron) to specific values to the next 4 items. Ignored by solvers.

Ms: Saturation magnetization in A/m.

A: Exchange stiffness in J/m.

K1: Crystalline anisotropy constant in J/m${}^3$. If $K1>0$, then the anisotropy axis (or axes) is an easy axis; if then the anisotropy axis is a hard axis.

Anisotropy Type: Crystalline anisotropy type; One of <uniaxial|cubic>.

Anisotropy Dir1: Directional cosines of first crystalline anisotropy axis, taken with respect to the coordinate axes (3 numbers). Optional; Default is 1 0 0 (x-axis).

Anisotropy Dir2: Directional cosines of second crystalline anisotropy axis, taken with respect to the coordinate axes (3 numbers). Optional; Default is 0 1 0 (y-axis).

For uniaxial materials it suffices to specify only Anisotropy Dir1. For cubic materials one must also specify Anisotropy Dir2; the third axis direction will be calculated as the cross product of the first two. The anisotropy directions will be automatically normalized if necessary, so for example 1 1 1 is valid input (it will be modified to .5774 .5774 .5774). For cubic materials, Dir2 will be adjusted to be perpendicular to Dir1 (by subtracting out the component parallel to Dir1).

Anisotropy Init: Method to use to set up directions of anisotropy axes, as a function of spatial location; This is a generalization of the Anisotropy Dir1/2 records. The value for this record should be one of <Constant|UniformXY|UniformS2>. Constant uses the values specified for Anisotropy Dir1 and Dir2, with no dispersion. UniformXY ignores the values given for Anisotropy Dir1 and Dir2, and randomly varies the anisotropy directions uniformly in the xy-plane. UniformS2 is similar, but randomly varies the anisotropy directions uniformly on the unit sphere ($S^2$). This record is optional; the default value is Constant.

Edge K1: Anisotropy constant similar to crystalline anisotropy constant K1 described above, but applied only along the edge surface of the part. This is a uniaxial anisotropy, directed along the normal to the boundary surface. Units are J/m${}^3$, with positive values making the surface normal an easy axis, and negative values making the surface an easy plane. The default value for Edge K1 is 0, which disables the term.

Do Precess: If 1, then enable the precession term in the Landau-Lifshitz ODE. If 0, then do pure damping only. (Optional; default value is 1.)

Gyratio: The Landau-Lifshitz gyromagnetic ratio, in m/(A.s). This is optional, with default value of $2.21\times {10}^5$. See the discussion of the Landau-Lifshitz ODE under the Damp Coef record identifier description.

Damp Coef: The ODE solver in OOMMF integrates the Landau-Lifshitz equation [12, 17], written as

$$\frac{d\text{𝐌}}{dt}=-|\overline{\gamma }|\text{𝐌}\times {\text{𝐇}}_{\mathrm{eff}}-\frac{|\overline{\gamma }|\alpha }{M_s}\text{𝐌}\times \left(\text{𝐌}\times {\text{𝐇}}_{\mathrm{eff}}\right),$$

where

	$\overline{\gamma }$		is the Landau-Lifshitz gyromagnetic ratio (m/(A$\cdot$s)),
	$\alpha$		is the damping coefficient (dimensionless).

(Compare to (7.2), page 7.2.) Here $\alpha$ is specified by the “Damp Coef” entry in the MIF 1.1 file. If not specified, a default value of 0.5 is used, which allows the solver to converge in a reasonable number of iterations. Physical materials will typically have a damping coefficient in the range 0.004 to 0.15. The 2D solver engine mmSolve requires a non-zero damping coefficient.