Cu and O NMR studies of the magnetic properties of YBa2Cu3O6.63 (Tc=62 K).
Cu and O NMR studies of the magnetic properties of YBa2Cu3O6.63 (Tc=62 K).
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DOI：
10.1103/physrevb.43.247
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发表时间：
1991
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影响因子：
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通讯作者：
M. Takigawa;Arneil Reyes;P. Hammel;J. D. Thompson;R. Heffner;Z. Fisk;Kevin C. Ott
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文献类型：
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作者：
M. Takigawa;Arneil Reyes;P. Hammel;J. D. Thompson;R. Heffner;Z. Fisk;Kevin C. Ott
物理综述B卷43，YBa 2Cu 306 M的磁性的Cu和O NMR研究。Takigawa，* A. P. Reyes，P. C.哈梅尔，1991年1月（T，=62 K）J. D.汤普森河，巴西-地H. Heffner，Z.菲斯克，K. C. Ott和Los Alamos Rational Laboratory，Los A/amos，Rem Mexico 87544（1990年4月30日接收）在Cu和NMR实验中研究了YBa 2Cu 306 63（T =62 K）中Cu O 2平面的微观磁性。与完全氧化的Y-Ba-Cu-07（T =90 K）不同，在正常状态下，Cu和Knight-shift张量的各种组分显示出强烈但相同的温度依赖性。这支持了在Cu 02平面中仅存在一个自旋分量的图片。在正常态下，由Knight-shift结果导出的自旋极化率随温度的降低而显著降低。的核自旋弛豫速率（1/T&）的温度依赖性是非常不同的Cu和网站。1/（T& T）与自旋磁化率几乎成正比。1/（T& T）在150 K附近有一个宽峰。我们讨论了这些弛豫行为的基础上提出的动力学自旋磁化率的模型米利斯，Monien，和松树。I.磁性所起的作用，特别是性质是高温铜氧化物超导体的中心问题之一。磁性的重要性是由超导相接近反铁磁绝缘相的组成是改变。在诸如La 2CuO 4和YBazCu 3 O 6等反铁磁绝缘体中，二维（2D）CuO 2层中的每个Cu原子具有2+价态（3d配置）。这些化合物的基态和磁激发可用2D，s = -，' Heisenberg模型很好地描述。长程反铁磁有序很容易通过在CuO 2平面中掺杂少量额外的空穴而被破坏。对于足够的掺杂，系统变成金属和超导。各种高能光谱数据表明，这些掺杂的空穴主要占据2 p态，使Cu的价态为2+。Ya_2Cu_（307）的γ和γ的Knight-shift结果有力地支持了掺杂空穴进入0 ~ 2 p态的事实。在SrCu 04（参考文献8）和YBa 2Cu 307（参考文献9）上进行的中子散射实验表明短程反铁磁关联持续到超导相。然而，一个适当的描述磁相关仍然是一个有争议的问题。这里的一个重要问题是Cu 3d和2 p空穴是否具有不同的自旋自由度和不同的自旋动力学，或者这些态之间的杂化是否如此强烈以至于系统由具有独特动力学的单个自旋分量描述。张和赖斯提出了后一种情况的一个特殊模型。他们提出，掺杂的空穴的自旋与相邻的Cu自旋形成一个局部单重态，具有如此大的单重结合能，0 - 2 p空穴对自旋磁化率没有贡献。也有可能超导材料已经被如此重掺杂，以致于自旋涨落、电荷转移能隙没有被清楚地定义，并且费米能级附近的状态以类似于重电子材料的方式由Cu d和p杂化带适当地描述。在这种情况下，磁性也由单自旋分量描述。核磁共振和四极共振（NMR和NQR）已被广泛用作高温化合物磁性的微观探针。这些技术的独特力量在于它们能够区分不同原子和不同晶体学位点的行为。最广泛的共振研究已经在Yaa 2Cu 3 O 7 y系统中完成，特别是在使用Cu、10和Y核的完全氧化（y =0）材料上。该系统的一个显著特点是可以通过改变氧含量γ来控制掺杂空穴浓度和超导转变温度（Ti）。特别地，迄今为止已知两个均匀相，一个y =0（Ti =90 K），另一个y =0。三比零5（T_i =60 K）。已有报道指出，60-K相的磁性能与完全氧化的材料有很大的不同。60-K相的磁化率y（T）随温度的降低而降低，与y =0材料中的T无关的Pauli-like磁化率相反，如图1所示。这种T依赖性部分地与CuO 2平面的自旋磁化率相关，如Y和Cu Knight-shift数据所揭示的。Y和Cu的核弛豫速率也显示出与详细的磁性本征- y =0材料完全不同的行为。这些关系取决于样品制备方法以及氧含量的精确值和均匀性，重要的是对单个样品进行各种NMR测量。这一动机使我们对表征良好的YBa 2Cu 3 O 6 63（y =0. 37)样品，其结果如下所示。美国物理学会
PHYSICAL REVIEW B VOLUME 43, NUMBER Cu and O NMR studies of the magnetic properties of YBa2Cu306 M. Takigawa, * A. P. Reyes, P. C. Hammel, JANUARY 1991 (T, =62 K) J. D. Thompson, R. H. Heffner, Z. Fisk, K. C. Ott and Los Alamos Rational Laboratory, Los A/amos, Rem Mexico 87544 (Received 30 April 1990) The microscopic magnetic properties of the Cu02 planes in YBa2Cu306 63 (T, =62 K) have been investigated in Cu and NMR experiments. Unlike the fully oxygenated Y-Ba-Cu-07 (T, =90 K), the various components of the Cu and Knight-shift tensors show strong but identical temperature dependences in the normal state. This supports the picture that there is only one spin component in the Cu02 planes. The spin susceptibility deduced from Knight-shift results shows significant reduc- tion with decreasing temperature in the normal state. The temperature dependences of the nuclear-spin-relaxation rates (1/T& ) are very different for the Cu and the sites. 1/( T& T) at the O sites is nearly proportional to the spin susceptibility. 1/(T& T) at the Cu sites shows a broad peak around 150 K. We discuss these relaxation behaviors based on a model of the dynamical spin sus- ceptibility proposed by Millis, Monien, and Pines. I. INTRODUCTION The role played by magnetism, particularly the nature is one of the central issues of the high-T, copper oxide superconductors. The importance of magnetism is suggested by the proximity of the super- conducting phase to the antiferromagnetic insulating phase as the composition is changed. In the antiferro- magnetic insulators such as La2Cu04 and YBazCu306, each Cu atom in the two-dimensional (2D) Cu02 layers has 2+ valence (3d configuration). The ground state and the magnetic excitations of these compounds are well described by a 2D, s = —, ' Heisenberg model. ' The long-range antiferromagnetic order is easily destroyed by doping a small number of additional holes into the Cu02 planes. For sufficient doping the system becomes metallic and superconducting. Various high-energy spectroscopic data show that these doped holes mostly occupy the 2p states leaving the Cu valence to be 2+. ' ' and Y Knight-shift results on Yaa2Cu307 strongly support the fact that doped holes go into the 0 2p states. ' Neutron-scattering experiments performed on Sr Cu04 (Ref. 8) and YBazCu307 (Ref. 9) re- La& vealed that short-range antiferromagnetic correlations persist into the superconducting phase. However, an ap- propriate description of the magnetic correlations is still a subject of controversy. An important problem here is whether the Cu 3d and 2p holes have distinct spin de- grees of freedom and different spin dynamics' or wheth- er the hybridization between these states is so strong that the system is described by a single spin component with unique dynamics. A particular model of the latter case was presented by Zhang and Rice. They proposed that the spin of a doped hole forms a local singlet state with the neighboring Cu spin with such a large singlet binding energy that 0 2p holes make no contribution to the spin susceptibility. It may also be possible that the supercon- ducting materials are already so heavily doped that the of spin fluctuations, charge-transfer gap is not clearly defined and the states near the Fermi level are properly described by the Cu d and p hybridized band in a way similar to the heavy electron materials. ' In this case, the magnetic properties are described also by a single-spin component. Nuclear magnetic and quadrupole resonance (NMR and NQR) have been extensively used as microscopic probes of the magnetic properties of high-T, compounds. The unique power of these techniques lies in their capa- bility to distinguish behaviors at different atoms and different crystallographic sites. The most extensive reso- nance studies have been done in the Yaa2Cu307 y sys- tem, particularly on the fully oxygenated (y =0) material, using Cu, ' 0, and Y nuclei. A significant feature of this system is that one can control the concentration of doped holes and the superconducting transition tempera- ture (T, ) by changing the oxygen content y. ' In particu- lar, two homogeneous phases are known so far, one with y =0 (T, =90 K) and the other with y =0. 3 — 0. 5 (T, =60 K). It has already been reported that the magnetic proper- ties of the 60-K phase are very different from those of ful- ly oxygenated material. The magnetic susceptibility y( T) of the 60-K phase decreases with decreasing tempera- ture, ' in contrast to the T-independent Pauli-like suscep- tibility in the y =0 material, as shown in Fig. 1. This T dependence is partly associated with the spin susceptibili- ty of the Cu02 plane as revealed by the Y and Cu Knight-shift data. The Y and Cu nuclear relaxa- tion rates also show quite different behaviors from the Since the detailed magnetic proper- y =0 material. ties depend on the sample preparation method as well as the precise value and homogeneity of the oxygen content, it is important to make various NMR measurements on a single sample. This motivation led us to perform Cu and ' NMR experiments on a well-characterized YBa2Cu306 63 (y =0. 37) sample, the results of which are presented below. The American Physical Society