Low‐temperature and alternating field demagnetization of saturation remanence and thermoremanence in magnetite grains (0.037 μm to 5 mm)
Low‐temperature and alternating field demagnetization of saturation remanence and thermoremanence in magnetite grains (0.037 μm to 5 mm)
复制标题
磁铁矿晶粒饱和剩磁和热剩磁的低温交变场退磁（0.037μm至5mm）
DOI：
--
复制
发表时间：
1992
期刊：
影响因子：
--
通讯作者：
H. Soffel
中科院分区：
文献类型：
--
作者：
F. Heider;D. Dunlop;H. Soffel
对不同来源、粒度为0.037 μm ~ 5 mm的磁铁矿进行了低温退磁（LTD）实验，测量了其饱和等温剩磁（IRMs）和0.1mT热剩磁（TRM）的记忆分数RI和RT，并与实验结果进行了比较。在10 μm以下，具有很强的本征晶粒尺寸依赖性，而在10 μm以上的多畴（MD）范围内，几乎与尺寸无关。Parry [1979，1980]报告的MD范围内RI和RT的尺寸依赖性可能是由于在破碎过程中引入应力以获得更细的尺寸级分。我们证明，磁铁矿的制备方法，晶体中的不规则性，以及通过淬火或退火来增加或减少内应力的状态都对磁记忆的量有直接的影响。磁性存储器（LTD后残留的TRM和IRM 5部分）比LTD前的原始TRM和IRMs更能抵抗交变磁场（AF）退磁。即使是大的磁铁矿晶体（20 μm）也显示出坚硬，单域-比较了这些MD磁铁矿中IRMs和TRM的AF退磁特性，结果表明，Lowrie和Fuller [1971]检验必须重新解释。
Low-temperature demagnetization (LTD), consisting of zero-field cycling from room temperature to 77 K and back to room temperature, was performed on magnetites from different sources having grain sizes between 0.037 μm and 5 mm. The memory fractions, RI and RT of saturation isothermal remanent magnetization (IRMs) and 0.1 mT thermoremanent magnetization (TRM), respectively, have a strong intrinsic grain-size dependence below ≈ 10 μm, but are almost size independent in the multidomain (MD) range above 10 μm. The size dependence of RI and RT in the MD range reported by Parry [1979, 1980] probably results from stress introduced during crushing to obtain finer size fractions. We demonstrate that the method of preparation of magnetites, irregularities in the crystals, and increase or decrease of the state of internal stress by quenching or annealing all have a direct effect on the amount of magnetic memory. Magnetic memories (the fractions of TRM and IRM5 surviving after LTD) are much more resistant against alternating-field (AF) demagnetization than the original TRM and IRMs before LTD. Even large magnetite crystals (≫20 μm) reveal a hard, single-domain-like component of magnetization when the softer magnetization is removed by LTD. A comparison of AF demagnetization properties of IRMs and TRM in these MD magnetites shows that the Lowrie and Fuller [1971] test must be reinterpreted.