To cite mirt in publications use:

R. Philip Chalmers (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48(6), 1-29. URL http://www.jstatsoft.org/v48/i06/.

Corresponding BibTeX entry:

  @Article{,
    title = {{mirt}: A Multidimensional Item Response Theory Package
      for the {R} Environment},
    author = {R. Philip Chalmers},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {48},
    number = {6},
    pages = {1--29},
    url = {http://www.jstatsoft.org/v48/i06/},
  }