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

The effect of magnetic field h on the longitudinal susceptibility in a spin S = 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 ( T m ) and position T m 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 h is weak, in a antiferromagnet, the height χ ( T m ) is a constant χ 0 which is independent of field and exchange anisotropy, but the position T m is only a function of the exchange anisotropy. While in a ferromagnet, both χ ( T m ) and T m are a function of field and the exchange anisotropy. (2) When the field h is strong, in a antiferromagnet, χ ( T m ) becomes dependent of field and the exchange anisotropy, and χ ( T m ) and T m are fitted satisfactory to power laws: χ ( T m ) − χ 0 ∝ h d and T N − T m ∝ h c , respectively. Here T N is the Neel temperature. On the contrary, in a ferromagnet, χ ( T m ) and T m are fitted to power laws: χ ( T m ) ∝ h − d ′ and T m − T c ∝ h c ′ , where T c is the Curie temperature. The above results are very useful in studying the magnetic property of coordination polymers.