17.1.5 Experiment parameters

The following records specify the applied field schedule:

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  Field Range: Specifies a range of applied fields that are stepped though in a linear manner. The parameter list should be 7 numbers, followed by optional control point (stopping criteria) specifications. The 7 required fields are the begin field Bx By Bz in Tesla, the end field Bx By Bz in Tesla, and an integer number of steps (intervals) to take between the begin and end fields (inclusive). Use as many Field Range records as necessary—they will be stepped through in order of appearance. If the step count is 0, then the end field is ignored and only the begin field is applied. If the step count is larger than 0, and the begin field is the same as the last field from the previous range, then the begin field is not repeated.

  The optional control point specs determine the conditions that cause the applied field to be stepped, or more precisely, end the simulation of the magnetization evolution for the current applied field. The control point specs are specified as –type value pairs. There are 3 recognized control point types: –torque, –time, and –iteration. If a –torque pair is given, then the simulation at the current applied field is ended when $\parallel \text{𝐦}\times \text{𝐡}\parallel$ (i.e., $\parallel \text{𝐌}\times \text{𝐇}\parallel /M_s^2$) at all spins in the simulation is smaller than the specified –torque value (dimensionless). If a –time pair is given, then the simulation at the current field is ended when the elapsed simulation time for the current field step reaches the specified –time value (in seconds). Similarly, an –iteration pair steps the applied field when the iteration count for the current field step reaches the –iteration value. If multiple control point specs are given, then the applied field is advanced when any one of the specs is met. If no control point specs are given on a range line, then the Default Control Point Spec is used.

  For example, consider the following Field Range line:

     Field Range: 0 0 0 .05 0 0  5  -torque 1e-5 -time 1e-9
  

  This specifies 6 applied field values, (0,0,0), (0.01,0,0), (0.02,0,0), …, (0.05,0,0) (in Tesla), with the advancement from one to the next occurring whenever $\parallel \text{𝐦}\times \text{𝐡}\parallel$ is smaller than 1e-5 for all spins, or when 1 nanosecond (simulation time) has elapsed at the current field. (If –torque was not specified, then the applied field would be stepped at 1, 2, 3 4 and 5 ns in simulation time.)

  The Field Range record is optional, with a default value of 0 0 0 0 0 0 0.

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  Default Control Point Spec: List of control point –type value pairs to use as stepping criteria for any field range with no control point specs. This is a generalization of and replacement for the Converge $\mathrm{|}$mxh$\mathrm{|}$ Value record. Optional, with default “-torque 1e-5.”

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  Field Type: Applied (external) field routine and parameters, if any. This is optional, with default Uniform. At most one record of this type is allowed, but the Multi type may be used to apply a collection of fields. The nominal applied field (NAF) is stepped through the Field Ranges described above, and is made available to the applied field routines which use or ignore it as appropriate.

  The following Field Type routines are available:

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    Uniform
    Applied field is uniform with value specified by the NAF.

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    Ribbon relcharge x0 y0 x1 y1 height
    Charge “Ribbon,” lying perpendicular to the $xy$-plane. Here relcharge is the charge strength relative to Ms, and (x0,y0), (x1,y1) are the endpoints of the ribbon (in meters). The ribbon extends height/2 above and below the calculation plane. This routine ignores the NAF.

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    Tie rfx rfy rfz x0 y0 x1 y1 ribwidth
    The points (x0,y0) and (x1,y1) define (in meters) the endpoints of the center spine of a rectangular ribbon of width ribwidth lying in the $xy$-plane. The cells with sample point inside this rectangle see an applied field of (rfx,rfy,rfz), in units relative to Ms. (If the field is large, then the magnetizations in the rectangle will be “tied” to the direction of that field.) This routine ignores the NAF.

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    OneFile filename multiplier
    Read B field (in Tesla) in from a file. Each value in the file is multiplied by the “multiplier” value on input. This makes it simple to reverse field direction (use -1 for the multiplier), or to convert H fields to B fields (use 1.256637e-6). The input file may be any of the vector field file types recognized by mmDisp. The input dimensions will be scaled as necessary to fit the simulation grid, with zeroth order interpolation as necessary. This routine ignores the NAF.

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    FileSeq filename procname multiplier
    This is a generalization of the OneFile routine that reads in fields from a sequence of files. Here “filename” is the name of a file containing Tcl code to be sourced during problem initialization, and “procname” is the name of a Tcl procedure defined in filename, which takes the nominal B field components (in Tesla) and field step count values as imports (4 values total), and returns the name of the vector field file that should be used as the applied B field for that field step. The B field units in the vector field file should be Tesla.

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    Multi routinecount \
    param1count name1 param1 param2 …\
    param2count name2 param1 param2 …\
    …
    Allows a conglomeration of several field type routines. All entries must be on the same logical line, i.e., end physical lines with ’\’ continuation characters as necessary. Here routinecount is the number of routines, and param1count is the number parameters (including name1) needed by the first routine, etc.

  Note that all lengths are in meters. The coordinates in the simulation lie in the first octant, running from (0,0,0) to (Part Width, Part Height, Part Thickness).