code: def plot_xtf(fignum, XTF, Fs, e, b):
      
      plt.figure(num=fignum)
      plt.xlabel('Temperature (K)')
      plt.ylabel('Susceptibility (m^3/kg)')
      k = 0
      Flab = []
      for freq in XTF:
          T, X = [], []
          for xt in freq:
              X.append(xt[0])
              T.append(xt[1])
          plt.plot(T, X)
          plt.text(T[-1], X[-1], str(int(Fs[k])) + ' Hz')
  #        Flab.append(str(int(Fs[k]))+' Hz')
          k += 1
      plt.title(e + ': B = ' + '%8.1e' % (b) + ' T')
docs: function to plot series of chi measurements as a function of temperature, holding field constant and varying frequency