在Fe3O4纳米晶体中对表面旋转效应对旋转放松的时间解析研究
Chih-Hao Hsia1, Tai-Yen Chen, Dong Hee Son
1Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA.
Journal of the American Chemical Society
|July 2, 2009
概括
表面旋转显著影响氧化铁纳米晶体中的磁化放松. 这项研究表明,表面旋转在放松方面比Fe(3) O(4) 纳米晶体内的内部旋转有效三倍.
科学领域:
- 材料科学 材料科学 材料科学
- 纳米技术 纳米技术
- 固态物理 固态物理
背景情况:
- 磁纳米粒子中的磁化放松动态对于它们的应用至关重要.
- 表面效应经常主导纳米材料的性能,因为表面面积与体积的比率很高.
- 了解氧化铁 (Fe(3) O(4)) 纳米晶体中的自旋放松机制是自旋电子设备的关键.
研究的目的:
- 为了研究表面旋转在光学激发Fe(3) O(4) 纳米晶体的磁化放松中的作用.
- 量化表面旋转相对于内部旋转在旋转放松中的相对效率.
- 为了将纳米晶体大小与磁化恢复动态相关联.
主要方法:
- 时间解析法拉第旋转测量被用来探测磁化动态.
- 用光学刺激来诱导去磁化.
- 用一个简单的模型来分析旋转格的放松率,并将其与旋转轨道合联系起来.
主要成果:
- 磁化恢复时间随着纳米晶体大小的增加,从5nm的250ps增加到15nmFe(3) O(4) 纳米晶体的350ps.
- 分析表明,表面旋转在旋转放松方面比内部旋转大约效率高三倍.
- 在表面放松分析中考虑了Fe(3) O(4) 纳米晶体的油酸被动化.
结论:
- 表面旋转在Fe(3) O(4) 纳米晶体的旋转放松中发挥着主导作用.
- 表面旋转的增强放松效率是纳米磁铁动态的一个关键因素.
- 这些发现对磁性纳米材料在数据存储和生物医学成像等领域的设计和应用有影响.
![Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59399.jpg&w=3840&q=50)
相关概念视频
01:28Atomic Nuclei: Types of Nuclear Relaxation
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
01:23Atomic Nuclei: Nuclear Relaxation Processes
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:03Atomic Nuclei: Nuclear Spin State Overview
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
01:31Ferromagnetism
Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...