中文摘要：

以双量子位Heisenberg模型为例，讨论了磁场方向对纠缠的影响。结果表明：一定温度下，保持磁场的大小不变，仅改变其方向，不仅能获得最大纠缠，还产生了量子相变。

英文摘要：

The effect of orientation in the magnetic field on the entanglement of a two-qubit Heisenberg model is in- vestigated. It is found that the maximum entanglement can be obtained by changing direction of the magnetic field with fixed magnitude at given temperature, i.e. driven by orientation of magnetic field. One of the most interesting facts, at zero temperature, is that quantum phase transition（QPT） can be take place through rotating the magnetic field. This can be regarded as magnetic direction induced QPT.