Ground-state spin dynamics of ErCo2
Ground-state spin dynamics of ErCo2
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ErCo2 的基态自旋动力学
DOI：
10.1103/physrevb.23.207
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发表时间：
1981
影响因子：
3.7
通讯作者：
J. Rhyne
中科院分区：
文献类型：
--
作者：
N. Koon;J. Rhyne
我们利用中子非弹性散射研究了4.2 K时erco 2的基态磁激发谱。观察到四种模式，其中两种是非色散的，两种是弱色散的。每个弱色散模在区边界处与一个非色散模简并，但在区中心处能量下降。从激发的动态结构因子可以得出非色散模式对应于原始细胞中两个稀土自旋的相外进动，而弱色散模式对应于相内进动。使用标准基算符来解释晶体电场的格林函数随机相位近似理论很好地描述了结果，我们发现晶体电场的强度与交换相互作用相当。所观察到的激发模式与er3 +基态到第二和第四激发态的跃迁有关。通过拟合模式的能量和强度，我们确定了jer - er = 0±0.01 meV, jer - c0 = - 0.153 meV, a40 = 4.3 meV/ a0.4, a60 = - 0.142 meV/ a0.6。我们没有观察到理论所预测的以Co为主的自旋波模式，这可能表明海森堡模型在应用于Co自旋时的崩溃。然而，对观测模态的计算几乎与Co子晶格的动力学假设无关。
We have studied the ground-state magnetic excitation spectrum of Er Co 2 at 4.2 K using neutron inelastic scattering. Four modes were observed, two which are nondispersive and two which are weakly dispersive. Each of the weakly dispersive modes is degenerate with one of the nondispersive modes at the zone boundary, but falls lower in energy at the zone center. From the dynamic structure factor of the excitations we conclude that the nondispersive modes correspond to out-of-phase precession of the two rare-earth spins in the primitive cell, while the weakly dispersive modes correspond to in-phase precession. The results are described very well by a Green's-function random-phase-approximation theory using standard basis operators to account for the crystalline electric fields, which we find to be comparable in strength to the exchange interactions. The observed excitation modes are associated with transitions from the Er 3+ ground state to the second and fourth excited states. By fitting the energies and intensities of the modes we determine J E r− E r= 0±0.01 meV, J E r− C o=− 0.153 meV, A 4 0= 4.3 meV/a 0 4, and A 6 0=− 0.142 meV/a 0 6. We did not observe a predominantly Co spin-wave mode predicted by the theory, which may indicate a breakdown of the Heisenberg model when applied to the Co spins. Calculations for the observed modes, however, are nearly independent of the dynamics assumed for the Co sublattice.