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首页> 外文期刊>Physical review >Anisotropic spin fluctuations and anomalies of nuclear quadrupole interactions in the itinerant antiferromagnet NpCoGa_5: ~(59)Co NMR and ~(69,71)Ga NMR/NQR studies
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Anisotropic spin fluctuations and anomalies of nuclear quadrupole interactions in the itinerant antiferromagnet NpCoGa_5: ~(59)Co NMR and ~(69,71)Ga NMR/NQR studies

机译：流动反铁磁体NpCoGa_5中的各向异性自旋涨落和核四极相互作用的异常：〜（59）Co NMR和〜（69,71）Ga NMR / NQR研究

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Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments have been performed on a single crystal of tetragonal NpCoGa_5, an itinerant antiferromagnet with a Neel temperature T_N =47 K. The antiferromagnetic phase is inverted to a field-induced ferromagnetic (FIF) phase with an applied field (H_0) above H_m (T→0) ～40 kOe oriented along the c axis. NMR spectra have been measured above and below T_N with H_0‖c and a axes and have been assigned to ~(69,71)Ga nuclei on two crystallographically inequiva-lent 1c and 4i sites and to ~(59)Co nuclei on the 1b site. Using second-order perturbation calculations, Knight shift (K), electric field gradient (EFG), frequency (ν_Q), and asymmetry parameter (η) of the EFG are deduced for each site. These parameters for the ~(69)Ga(1c) and ~(69,71)Ga(4i) sites are confirmed by NQR measurements in zero field. The Knight shifts obtained in the paramagnetic (PM) state obey a Curie-Weiss law, which scales with the bulk susceptibility (χ). Hyperfine tensors for each site are deduced from K-χ plots with temperature as an implicit parameter. Antiferromagnetic NMR spectra in zero field were also observed, finding an internal field of ～20 kOe at the Ga(4i) site at the lowest temperature. The ordered moment can be estimated from this to be 0.81 μ_B/Np. The nuclear quadrupolar parameters (ν_Q and η) are found to exhibit an anomaly just below T_N in the FIF phase. T_1 and T_2 have been measured for each site. For H_0‖c, T_1 ～ constant behavior suggests localized 5f character for T > 100 K and itinerant (1/T_1 ∝ T) behavior for T_N < T < ～ 100 K in NpCoGa_5. T_2 measure- ments in the case of H_0‖c clearly define a phase crossover between PM and FIF phases. A sharp anisotropy for spin fluctuations in NpCoGa_5 has also been demonstrated.
机译：已经对四角形NpCoGa_5单晶进行了核磁共振（NMR）和核四极共振（NQR）实验，该NeCoGa_5是Neel温度T_N = 47 K的流动性反铁磁体。 ）相，其作用域（H_0）沿c轴在H_m（T→0）〜40 kOe以上。 NMR谱在T_N的上方和下方用H_0′c和一个轴进行了测量，并已分配给两个晶体学上不等价的1c和4i位点上的〜（69,71）Ga核和1b上的〜（59）Co核。现场。使用二阶扰动计算，可以得出每个站点的奈特偏移（K），电场梯度（EFG），频率（ν_Q）和不对称参数（η）。 〜（69）Ga（1c）和〜（69,71）Ga（4i）位点的这些参数通过零场中的NQR测量来确认。在顺磁性（PM）状态下获得的奈特位移服从居里-魏斯定律，该定律随整体磁化率（χ）成比例。从K-χ图推导出每个位置的超精细张量，其中温度作为隐式参数。还观察到了零磁场下的反铁磁NMR光谱，在最低温度下，Ga（4i）处的内部磁场为〜20 kOe。由此可以估计出阶跃矩为0.81μB/ Np。发现在FIF阶段，核四极参数（ν_Q和η）在T_N之下显示出异常。已针对每个站点测量了T_1和T_2。对于H_0′c，在NpCoGa_5中，T_1〜恒定的行为表示T> 100 K的局部5f字符，而T_N

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