Balan Ana, Derlet Peter M, Rodríguez Arantxa Fraile, Bansmann Joachim, Yanes Rocio, Nowak Ulrich, Kleibert Armin, Nolting Frithjof
Swiss Light Source, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
Condensed Matter Theory Group, NUM, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
Phys Rev Lett. 2014 Mar 14;112(10):107201. doi: 10.1103/PhysRevLett.112.107201. Epub 2014 Mar 10.
X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times.
结合X射线磁圆二色性的X射线光电子能谱显微镜用于研究尺寸范围从20纳米至8纳米的单个铁纳米颗粒的磁性。虽然块状铁的磁晶各向异性表明在此尺寸范围内呈现超顺磁性行为，但在所有尺寸的颗粒中也发现了铁磁阻塞颗粒。在单个颗粒中观察到了从阻塞状态到超顺磁状态的自发转变，这表明铁磁颗粒中增强的磁能垒是由于具有意外寿命的亚稳态结构激发态所致。
