Static magnetic order in Na 0.75 CoO 2 detected by muon spin rotation and relaxation
Static magnetic order in Na 0.75 CoO 2 detected by muon spin rotation and relaxation
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DOI：
10.1103/physrevb.67.214420
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发表时间：
2003-05
影响因子：
3.7
通讯作者：
J. Sugiyama;H. Itahara;J. Brewer;E. Ansaldo;T. Motohashi;M. Karppinen;H. Yamauchi
中科院分区：
文献类型：
--
作者：
J. Sugiyama;H. Itahara;J. Brewer;E. Ansaldo;T. Motohashi;M. Karppinen;H. Yamauchi
使用 300 至 2.5 K 温度范围内的多晶样品，通过正 μ 子自旋旋转和弛豫 $({\ensuremath{\mu}}^{+}\mathrm{SR})$ 光谱研究了富钠热电 ${\mathrm{Na}}_{0.75}{\mathrm{CoO}}_{2}$ 在 22 K 时磁转变的性质。 零场$\ensuremath{\mu}\mathrm{SR}$测量表明在低于22 K的温度下存在静态内部磁场${(=T}_{\mathrm{m}})。$观测到的低于${T}_{\mathrm{m}}$的μ子自旋进动信号由具有不同进动频率的三个分量组成，对应于三个不等价的${\ensuremath{\mu}}^{+}$位点在 ${\mathrm{Na}}_{0.75}{\mathrm{CoO}}_{2}$ 晶格中。 2.5 K 时，三种成分的总体积分数估计为 $\ensuremath{\sim}21%$；因此，这种磁转变不是由杂质引起的，而是样品磁性的内在变化，尽管样品在其他方面是磁性不均匀的。另一方面，对 ${\mathrm{Na}}_{0.65}{\mathrm{CoO}}_{2}$ 样品进行的类似实验在低至 2.5 K 时没有表现出磁转变；这表明 Co 离子的平均价态是引起 22 K 磁转变的原因。
The nature of the magnetic transition of the Na-rich thermoelectric ${\mathrm{Na}}_{0.75}{\mathrm{CoO}}_{2}$ at 22 K was studied by positive muon-spin-rotation and relaxation $({\ensuremath{\mu}}^{+}\mathrm{SR})$ spectroscopy, using a polycrystalline sample in the temperature range between 300 and 2.5 K. Zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements indicated the existence of a static internal magnetic field at temperatures below 22 K ${(=T}_{\mathrm{m}}).$ The observed muon-spin precession signal below ${T}_{\mathrm{m}}$ consisted of three components with different precession frequencies, corresponding to three inequivalent ${\ensuremath{\mu}}^{+}$ sites in the ${\mathrm{Na}}_{0.75}{\mathrm{CoO}}_{2}$ lattice. The total volume fraction of the three components was estimated as $\ensuremath{\sim}21%$ at 2.5 K; thus, this magnetic transition was not induced by impurities but is an intrinsic change in the magnetism of the sample, although the sample was magnetically inhomogeneous otherwise. On the other hand, a similar experiment on a ${\mathrm{Na}}_{0.65}{\mathrm{CoO}}_{2}$ sample exhibited no magnetic transition down to 2.5 K; which indicates that the average valence of the Co ions is responsible for inducing the magnetic transition at 22 K.