Beyond Neel's theories:: thermal demagnetization of narrow-band partial thermoremanent magnetizations
Beyond Neel's theories:: thermal demagnetization of narrow-band partial thermoremanent magnetizations
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DOI：
10.1016/s0031-9201(01)00243-6
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发表时间：
2001-10-01
影响因子：
2.3
通讯作者：
Özdemir, Ö
中科院分区：
文献类型：
--
作者：
Dunlop, DJ;Özdemir, Ö
在一个狭窄的温度区间，T = 370 - 350 ℃，部分热还原磁化（pTRM）赋予一组粉碎和退火的天然磁铁矿样品，粒度范围从约1到125 - 150 μ m，畴状态从小的伪单畴（PSD）到多畴（MD）。通过这种方式，有效地激活了pTRM的单个阻断温度T-B。逐步热退磁没有擦除的pTRM急剧在T-B，为单域（SD）晶粒。退磁开始远低于350 ℃，并继续高于370 ℃，与一个中位数的解封温度，T-UB，接近360 ℃。最大的晶粒偏离SD行为。他们的pTRM在从室温到居里点的整个区间内退磁，与MD晶粒的预测一致。在解阻塞温度分布f（T-UB）或热退磁曲线的斜率dM/dT方面，SD晶粒具有尖锐的谱，T-UB = T-B;观察到MD晶粒具有以T-B为中心的宽的、大致对称的谱;并且PSD范围内的中等尺寸晶粒具有非高斯谱，结合了T-B附近的中心峰与T-B上方和下方的宽尾。在这方面，PSD晶粒显示SD和MD剩磁的叠加，而不是两者之间的混合。这些意见的实际意义是，Thellier的互易性（T-UB = T-B）的法律将越来越违反晶粒尺寸的PSD范围内的增加。f（T-UB）的低T-UB部分在Thellier型古强度测定的低温加热步骤中产生异常大的NRM退磁和Arai图的下垂形状。f（T-UB）的高T-UB部分导致热退磁中T-B处及以上的未磁化剩磁。在预处理设计，使剩磁更像SD在随后的热清洗，交变磁场（AF）预清洗锐化f（T-UB）更有效地比低温退磁的20妈妈样品。(C)2001爱思唯尔科技有限公司。保留所有权利。
Partial thermoremanent magnetization (pTRM) was imparted over a narrow temperature interval, T = 370-350 degreesC, to a suite of crushed and annealed natural magnetite samples, ranging in grain size from approximate to1 to 125-150 mum and in domain state from small pseudo-single-domain (PSD) to multidomain (MD). In this way, effectively a single blocking temperature, T-B, of pTRM was activated. Stepwise thermal demagnetization did not erase the pTRMs sharply at T-B, as for single-domain (SD) grains. Demagnetization began well below 350 degreesC and continued above 370 degreesC, with a median unblocking temperature, T-UB, close to 360 degreesC. The largest grains deviated most from SD behavior. Their pTRM demagnetized over the entire interval from room temperature to the Curie point, in accordance with predictions for MD grains. In terms of the unblocking temperature distribution f(T-UB) or slope dM/dT of the thermal demagnetization curve, SD grains have a sharp spectrum, T-UB = T-B; MD grains were observed to have a broad, roughly symmetrical spectrum centered on T-B; and intermediate size grains in the PSD range had non-Gaussian spectra, combining a central peak near T-B with broad tails above and below T-B. In this respect, PSD grains display a superposition of SD and MD remanences, not a blend between the two. Practical implications of these observations are that Thellier's law of reciprocity (T-UB = T-B) will be increasingly violated as grain size increases in the PSD range. The low-T-UB part of f(T-UB) produces anomalously large demagnetization of NRM in low-temperature heating steps of Thellier-type paleointensity determinations and a sagging shape of the Arai plot. The high-T-UB part of f(T-UB) results in undemagnetized remanence at and above T-B in thermal demagnetization. Among pre-treatments designed to make remanence more SD-like in subsequent thermal cleaning, alternating field (AF) pre-cleaning sharpened f(T-UB) more effectively than low-temperature demagnetization for the 20 mum sample. (C) 2001 Elsevier Science B.V. All rights reserved.