NiNb_{2}O_{6} is an almost ideal realization of a 1D spin-1 ferromagnetic Heisenberg chain compound with weak unidirectional anisotropy. Using time-domain THz spectroscopy, we measure the low-energy electrodynamic response of NiNb_{2}O_{6} as a function of temperature and external magnetic field. At low temperatures, we find a magnonlike spin excitation, which corresponds to the lowest energy excitation at q∼0. At higher temperatures, we unexpectedly observe a temperature-dependent renormalization of the spin-excitation energy, which has a strong dependence on field direction. Using theoretical arguments, exact diagonalizations, and finite temperature dynamical Lanczos calculations, we construct a picture of magnon-magnon interactions that naturally explains the observed renormalization. We show how magnetic field strength and direction may be used to directly tune the sign of the magnon-magnon interaction. This unique scenario is a consequence of the spin-1 nature and has no analog in the more widely studied spin-1/2 systems.

中文翻译：

---

铁磁Spin-1链中的可调磁子相互作用。

NiNb_ {2} O_ {6}是具有弱单向各向异性的一维自旋1铁磁Heisenberg链化合物的理想实现。使用时域太赫兹光谱，我们测量了NiNb_ {2} O_ {6}作为温度和外部磁场的函数的低能电动响应。在低温下，我们发现了一种类似磁振子的自旋激发，它对应于q〜0处的最低能量激发。在更高的温度下，我们出乎意料地观察到自旋激发能的温度依赖性重新归一化，该归一化与场方向密切相关。使用理论参数，精确的对角化和有限的温度动态Lanczos计算，我们构造了磁振子-磁振子相互作用的图片，自然地解释了观测到的重归一化。我们展示了如何使用磁场强度和方向直接调整磁振子-磁振子相互作用的符号。这种独特的情况是spin-1性质的结果，在更广泛研究的spin-1 / 2系统中没有类似物。