The effect of magnetic field on the susceptibility maximum in the spatially anisotropic Heisenberg antiferromagnet

The effect of magnetic field hh on the longitudinal susceptibility in a spin S=1/2S=1/2 exchange anisotropic three-dimensional Heisenberg antiferromagnet, is studied by the double-time Green’s function method within Tyablikov approximation. The calculation results indicated that the height χ(Tm)χ(Tm) and position TmTm of the maximum of the longitudinal susceptibility display different behaviors related to the magnetic fields and exchange anisotropic parameters. These behaviors are very different from that in the exchange anisotropic Heisenberg ferromagnet in the magnetic field. The results are: (1) When the field hh is weak, in a antiferromagnet, the height χ(Tm)χ(Tm) is a constant χ0χ0 which is independent of field and exchange anisotropy, but the position TmTm is only a function of the exchange anisotropy. While in a ferromagnet, both χ(Tm)χ(Tm) and TmTm are a function of field and the exchange anisotropy. (2) When the field hh is strong, in a antiferromagnet, χ(Tm)χ(Tm) becomes dependent of field and the exchange anisotropy, and χ(Tm)χ(Tm) and TmTm are fitted satisfactory to power laws: χ(Tm)−χ0∝hdχ(Tm)−χ0∝hd and TN−Tm∝hcTN−Tm∝hc, respectively. Here TNTN is the Neel temperature. On the contrary, in a ferromagnet, χ(Tm)χ(Tm) and TmTm are fitted to power laws: χ(Tm)∝h−d′χ(Tm)∝h−d′ and Tm−Tc∝hc′Tm−Tc∝hc′, where TcTc is the Curie temperature. The above results are very useful in studying the magnetic property of coordination polymers.