Low-Noise YBa2Cu3O7 Nano-SQUIDs for Performing Magnetization-Reversal Measurements on Magnetic Nanoparticles
Low-Noise YBa2Cu3O7 Nano-SQUIDs for Performing Magnetization-Reversal Measurements on Magnetic Nanoparticles
复制标题
DOI：
10.1103/physrevapplied.3.044011
复制
发表时间：
2015-04-17
影响因子：
4.6
通讯作者：
Koelle, D.
中科院分区：
文献类型：
--
作者：
Schwarz, T.;Woelbing, R.;Koelle, D.
采用聚焦离子束构图技术制备了基于晶界约瑟夫森结的YBa_2Cu_3O_7（YBCO）直流纳米超导量子干涉器件（nano-SQUID）。电传输和噪声特性的表征在4.2 K的磁屏蔽环境中产生一个非常小的电感L的几个pH值的优化设备的几何形状。这又导致在热白噪声极限中磁通噪声值非常低，< 50 n Phi（0）/Hz（1/2），这产生几μ（B）/Hz（1/2）的自旋灵敏度（Phi（0）是磁通量量子，μ（B）是玻尔磁子）。我们观察到的频率依赖性过剩噪声高达7 MHz，这可以被消除的偏置反转读出只有部分。这种行为表明未知来源的波动的存在下，可能与缺陷引起的自旋在SrTiO 3基板。我们展示了使用YBCO纳米SQUID的小自旋系统的调查，通过放置一个39 nm直径的Fe纳米线封装在一个非优化的YBCO纳米SQUID顶部的碳纳米管和测量的Fe纳米线的磁化反转通过耦合到纳米SQUID的磁通量的变化的潜力。铁纳米线的磁化反转后测得的磁通信号是在非常好的协议与估计值，和确定的开关字段指示通过卷曲模式的纳米线的磁化反转。
We fabricate YBa2Cu3O7 (YBCO) direct-current nano-superconducting quantum-interference devices (nano-SQUIDs) based on grain-boundary Josephson junctions by focused-ion-beam patterning. Characterization of electric transport and noise properties at 4.2 K in a magnetically shielded environment yields a very small inductance L of a few pH for an optimized device geometry. This, in turn, results in very low values of flux noise < 50 n Phi(0)/Hz(1/2) in the thermal white-noise limit, which yields spin sensitivities of a few mu(B)/Hz(1/2) (Phi(0) is the magnetic flux quantum, and mu(B) is the Bohr magneton). We observe frequency-dependent excess noise up to 7 MHz, which can be eliminated only partially by bias reversal readout. This behavior indicates the presence of fluctuators of unknown origin, possibly related to defect-induced spins in the SrTiO3 substrate. We demonstrate the potential of using YBCO nano-SQUIDs for the investigation of small spin systems, by placing a 39-nm-diameter Fe nanowire encapsulated in a carbon nanotube on top of a nonoptimized YBCO nano-SQUID and by measuring the magnetization reversal of the Fe nanowire via the change of magnetic flux coupled to the nano-SQUID. The measured flux signals upon magnetization reversal of the Fe nanowire are in very good agreement with estimated values, and the determined switching fields indicate magnetization reversal of the nanowire via curling mode.