The influence of crystallinity on magnetic ordering in natural ferrihydrites
The influence of crystallinity on magnetic ordering in natural ferrihydrites
复制标题
结晶度对天然水铁矿磁有序的影响
DOI：
10.1180/claymin.1988.023.2.04
复制
发表时间：
1988
期刊：
影响因子：
1.5
通讯作者：
T. G. Quin
中科院分区：
文献类型：
--
作者：
E. Murad;L. H. Bowen;G. Long;T. G. Quin
在295K和4.2K温度范围内采集了三种不同结晶度的天然铁氧体的穆斯堡尔谱，用四极分裂双峰分布对室温光谱进行了最佳拟合，随着结晶度的降低，分布的半宽度(0.71-0.86 mm/S)增大，最大值(0.62-0.78 mm/S)向高四极分裂方向移动。随着温度的降低，出现了相当模糊的磁有序光谱成分，并逐渐取代了超顺磁性双重态。根据二重态和磁性六重态下的相对面积得出的115K到28K的阻断温度表明，平均粒子尺寸在∼5到3 nm之间。六重态较宽，可与超微细场的分布相适应。随着温度的降低，这些分布变窄，最大值向高场移动；超顺磁性的影响在4·2K不再明显。
Abstract Mössbauer spectra of three natural ferrihydrites of different crystallinities were collected between 295 and 4·2 K. Optimal fits of the room-temperature spectra were obtained using distributions of quadrupole-split doublets; half-widths of the distributions (0·71–0·86 mm/s) increased, and maxima (at 0·62–0·78 mm/s) shifted to higher quadrupole splittings with decreasing crystallinity. Rather poorly-defined magnetically-ordered spectral components appeared and gradually replaced the superparamagnetic doublets as temperatures were reduced. Blocking temperatures between 115 and 28 K, derived from the relative areas under the doublets and magnetic sextets, indicated average particle sizes between ∼ 5 and 3 nm. The sextets were relatively broad and could be fitted with distributions of hyperfine fields. These distributions narrowed and their maxima shifted to higher fields as temperatures decreased; the influence of superparamagnetism was no longer apparent at 4·2 K.