2-MAGNON RAMAN SCATTERING AND EXCHANGE INTERACTION IN ANTIFERROMAGNETIC KNIF3 AND K2NIF4 AND FERRIMAGNETIC RBNIF3
2-MAGNON RAMAN SCATTERING AND EXCHANGE INTERACTION IN ANTIFERROMAGNETIC KNIF3 AND K2NIF4 AND FERRIMAGNETIC RBNIF3
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DOI：
10.1103/physrevb.3.1709
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发表时间：
1971-01-01
期刊：
影响因子：
--
通讯作者：
OCONNOR, JR
中科院分区：
文献类型：
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作者：
CHINN, SR;ZEIGER, HJ;OCONNOR, JR
我们在反铁磁性氟化镍化合物KNiF3、K2NiF4和亚铁磁性RbNiF3中观察到了双磁振子激发下的5145Ar激光的拉曼散射。对于KNiF3的立方钙钛矿结构和K2NiF4的四方结构的二维反铁磁体的行为，实验结果与用格林函数方法计算的理论谱符合得很好。对于具有反平行自旋的两亚晶格Néel亚铁磁体的一般情况，我们回顾了这种方法。通过与该理论的比较，我们发现这两种材料的海森堡交换常数分别为J=70.5±0.8和77.0±2.0 cm−1。描述了实验观察到的双磁振子喇曼光谱的温度依赖关系，该光谱在两种情况下都保持在奈尔温度以上。对于六方相RbNiF3，利用磁振子辅助的光吸收和磁化率数据，计算了磁振子的色散关系，估算了主要交换常数。对于反铁磁性180Ni2+-F−-Ni2+超交换作用，这些值分别为48 cm−1和113 cm−1，Ni2+相互作用的小的次近邻作用常数约为4 cm−1。当考虑磁非磁振子束缚效应时，510 cm拉曼线的低温拉曼线是由两个不同的布里渊区边缘磁子引起的，这与我们的交换常数是一致的。用目前的交换参数进行Bethe-Peierls-Weiss分析，得到了接近实验值139K的居里温度，并预测了高温亚晶格磁化，与核磁共振测量结果很好地一致。最后，对这些氟化镍进行了比较，并与在其他磁性绝缘体上的实验结果进行了比较。
We have observed Raman scattering of 5145-Å argon-laser radiation by two-magnon excitations in the antiferromagnetic nickel fluorides KNi F 3 and K 2 Ni F 4 and ferrimagnetic RbNi F 3. For both the cubic perovskite structure of KNi F 3 and the tetragonal structure of K 2 Ni F 4, which behaves like a two-dimensional antiferromagnet, the experimental results are in excellent agreement with the theoretical spectra computed by a Green's-function technique. This method is reviewed for the general case of a two-sublattice Néel ferrimagnet with antiparallel spins. From a comparison with this theory, we find values of J= 70.5±0.8 and 77.0±2.0 cm− 1, respectively, for the Heisenberg exchange constants in these two materials. The experimentally observed temperature dependence of the two-magnon Raman spectra, which persists above the Néel temperature in both cases, is described. For hexagonal RbNi F 3, with the aid of magnon-assisted optical-absorption and magnetic-susceptibility data, we have calculated the magnon dispersion relations and estimated the dominant exchange constants. These values are 48 cm− 1 for the antiferromagnetic 180 Ni 2+-F−-Ni 2+ superexchange interaction and 113 cm− 1 for the 90 ferromagnetic interaction, with a small second-nearest Ni 2+ interaction constant approximately 4 cm− 1. The identification of the low-temperature Raman line at 510 cm− 1 as arising from two different Brillouin-zone-edge magnons is consistent with our exchange constants when magnon-magnon binding effects are taken into account. A Bethe-Peierls-Weiss analysis using the present exchange parameters gives a Curie temperature close to the experimental value, 139 K, and predicts high-temperature sublattice magnetizations in good agreement with the results of nuclear-magnetic-resonance measurements. Finally, comparisons are made among these nickel fluorides, and with results found from experiments in other magnetic insulators.