Spin Waves and Switching: The Dynamics of Exchange - Biased Co Core - CoO Shell Nanoparticles
Mikhail Feygenson, Xiaowei Teng, Sue E. Inderhees, Yuen Yiu, Wenxin Du, Weiqiang Han, Jinsheng Wen, Zhijung Xu, Andrey A. Podlesnyak, Jennifer L. Niedziela, Mar… 展开作者
Mikhail Feygenson, Xiaowei Teng, Sue E. Inderhees, Yuen Yiu, Wenxin Du, Weiqiang Han, Jinsheng Wen, Zhijung Xu, Andrey A. Podlesnyak, Jennifer L. Niedziela, Mark Hagen, Yiming Qiu, Craig M. Brown, Lihua Zhang, Meigan C. Aronson
The utility of nanoscaled ferromagnetic particles requires both stabilized moments and maximized switching speeds. During reversal, the spatial modulation of the nanoparticle magnetization evolves in time, and the energy differences between each new configuration are accomodated by the absorption or emission spin waves with different wavelengths and energy profiles. The switching speed is limited by how quickly this spin wave energy is dissipated. We present here the first observation of dispersing spin waves in a nanoscaled system, using neutron scattering to detect spin waves in the CoO shells of exchange biased Co core- CoO shell nanoparticles. Their dispersion is little affected by finite size effects, but the spectral weight shifts to energies and wave vectors which increase with decreasing system size. Core-shell coupling leads to a substantial enhancement of the CoO spin wave population above its conventional thermal level, suggesting a new mechanism for dissipating core switching energy.
Tunable exchange bias effect in magnetic Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Ti$_{0.1}$O$_3$ nanoparticles at temperatures up to 250 K
在磁性Bi $_{0.9}$ Gd $_{0.1}$ Fe $_{0.9}$ Ti $_{0.1}$ O $_3$纳米粒子中观察到了交换偏置（EB）效应。研究了磁场冷却对交换偏置效应的影响。交换偏置场（$H_{EB}$）的大小随冷却磁场的增加而增加，表明交换偏置效应的强度可通过场冷却来调节。还发现$H_{EB}$值依赖于温度。这种磁性可调的交换偏置在温度高达250 K的Bi $_{0.9}$ Gd $_{0.1}$ Fe $_{0.9}$ Ti $_{0.1}$ O $_3$纳米粒子可能是值得潜在的应用。
Inert shell coating for enhanced laser refrigeration of nanoparticles: application in levitated optomechanics
Sydney Quantum Academy（悉尼量子学院）；School of Mathematical and Physical Sciences, Macquarie University（麦考瑞大学数理科学学院）；ARC Centre of Excellence for Engineered Quantum Systems, Macquarie University（麦考瑞大学工程量子系统卓越研究中心）；School of Engineering, Macquarie University（麦考瑞大学工程学院）；ARC Centre for Nanoscale BioPhotonics, Macquarie University（麦考瑞大学纳米生物光子学中心）
Absence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles
我们提出了一个详细的原子图片的Co纳米粒子的氧化机制及其对磁性的影响，通过实验以下的演变的结构，化学成分，和磁性的个人，气相生长的Co纳米粒子在受控氧化。早期氧化发生在两步过程中，其特征在于：（i）初始形成随机分布在纳米颗粒表面的小CoO微晶，直到它们的聚结导致氧化物壳的结构完整和金属核的钝化;（ii）CoO壳逐渐转化为Co 3 O 4，伴随着由于纳米级Kirkendall效应而形成的空隙。Co纳米颗粒在阶段（i）期间保持对氧的高度反应性，证明不存在压力间隙，由此假定在低压下的低反应性。我们的研究结果提供了一个重要的基准，为更好地了解氧化钴纳米粒子的磁性，其催化反应中的性能具有潜在的影响。
