M = moment(obj,Name,Value)
M = moment(obj,Name,Value) calculates the spin expectation value
including the leading quantum and thermal fluctuations ( terms).
The magnon poulation is calculated at a given temperature integrated
over the Brillouin zone. To calculate the numerical integral the
Brillouin zone is sampled using Monte Carlo technique.
Triangular lattice antiferromagnet
The example calculates the spin expectation value at zero temperature on the triangular lattice Heisenberg antiferromagnet. The result can be compared with the following calculations: A. V Chubukov, S. Sachdev, and T. Senthil, J. Phys. Condens. Matter 6, 8891 (1994): and S. J. Miyake, J. Phys. Soc. Japan 61, 983 (1992): ( is a higher order term neglected here).
tri = sw_model('triAF',1) M = tri.moment('nRand',1e7) dS = 1-M.moment
dS = 0.2612
Square lattice antiferromagnet
The reduced moment of the Heisenberg square lattice antiferromagnet at zero temperature can be compared to the published result of D. A. Huse, Phys. Rev. B 37, 2380 (1988) .
sq = sw_model('squareAF',1) M = sq.moment('nRand',1e7) dS = 1-M.moment
dS = 0.1966 0.1966 0.1966 0.1966
- spinw object.
Name-Value Pair Arguments
- The number of random points in the Brillouin-zone, default value is 1000.
- Temperature, default value is taken from
obj.single_ion.Tand the unit is stored in spinw.unit with the default being K.
- Tolerance of the incommensurability of the magnetic propagation wavevector. Deviations from integer values of the propagation vector smaller than the tolerance are considered to be commensurate. Default value is .
- Tolerance on the energy difference of degenerate modes when diagonalising the quadratic form, default value is .
- Defines whether to provide text output. The default value is determined
fidpreference stored in swpref. The possible values are:
0No text output is generated.
1Text output in the MATLAB Command Window.
fidFile ID provided by the
fopencommand, the output is written into the opened file stream.
- structure, with the following fields:
momentSize of the reduced moments in a row vector with number of elements.
nRandNumber of random points.
objThe clone of the input