Changes in remanence, coercivity and domain state at low temperature in magnetite
Changes in remanence, coercivity and domain state at low temperature in magnetite
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DOI：
10.1016/s0012-821x(01)00562-3
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发表时间：
2002-01-15
影响因子：
5.3
通讯作者：
Moskowitz, BM
中科院分区：
文献类型：
--
作者：
Özdemir, Ö;Dunlop, DJ;Moskowitz, BM
平均尺寸为0.037，0.10和0.22 μ m的亚微米磁铁矿晶体在跨越Verwey转变（T-V近似为120 K）的磁滞特性和畴态发生重大变化。0.037 μ m晶体在室温T-0下的立方相中和低于T-v的单斜相中都是单畴（SD）。0.10和0.22 μ m晶体在室温T-0下具有SD和双畴（2D）状态的混合物，但主要是低于T-v的SD结构，与微磁计算一致。由于单斜磁铁矿的高晶体各向异性和磁致伸缩，矫顽力H-c在冷却通过T-v时增加，在亚微米磁铁矿中增加3-5倍，在1.3 mm单晶中增加40倍。因此，畴壁和SD力矩被有效地固定在T-v以下，使得在升温或降温时的所有剩磁变化都是可逆的。然而，在大约100 K和T-0之间，剩磁行为是可变的。饱和剩磁（SIRM）产生于单斜磁铁矿在5 K下降了70-100%，在升温通过T-v，与微小的恢复冷却回通过T-v（最终水平在5 K的23-37%的亚微米晶体和3%的1.3毫米晶体）。相比之下，在300 K下在立方相中产生的SIRM在从300 K冷却到120 K期间由于畴壁的连续再平衡而降低5-35%（亚微米）或> 95%（1.3 mm），但是通过T-v本身的冷却几乎没有进一步的变化。然而，亚微米磁铁矿失去了进一步的5-15%的剩磁时，再加热通过T-V。这些不可逆的变化，在整个T-V的循环，和量的变化，在确定亚微米磁铁矿粒度的潜在价值。这种不可逆性主要是由通过T-v冷却时的2D → SD转变引起的，这种转变保持或增强了剩磁，而通过T-v升温时的SD → 2D转变引起剩磁退磁。(C)2002 Elsevier Science B. V.保留所有权利。
Submicron magnetite crystals with mean sizes of 0.037, 0.10 and 0.22 mum undergo major changes in hysteresis properties and domain states in crossing the Verwey transition (T-v approximate to 120 K). The 0,037 mum crystals are single-domain (SD) both in the cubic phase at room temperature T-0 and in the monoclinic phase below T-v. The 0.10 and 0.22 mum crystals have a mixture of SD and two-domain (2D) states at room temperature T-0 but mainly SD structures below T-v, in agreement with micromagnetic calculations. Coercive force H-c increases on cooling through T-v, by a factor 3-5 in the submicron magnetites and 40 in a 1.3 mm, single crystal, because of the high crystalline anisotropy and magnetostriction of monoclinic magnetite. As a result, domain walls and SD moments are so effectively pinned below T-v that all remanence variations in warming or cooling are reversible. However, between approximate to 100 K and T-0, remanence behavior is variable. Saturation remanence (SIRM) produced in monoclinic magnetite at 5 K drops by 70-100% in warming across T-v, with minor recovery in cooling back through T-v (ultimate levels at 5 K of 23-37% for the submicron crystals and 3% for the 1.3 mm crystal). In contrast, SIRM produced in the cubic phase at 300 K decreases 5-35% (submicron) or > 95% (1.3 mm) during cooling from 300 to 120 K due to continuous re-equilibration of domain walls, but there is little further change in cooling through T-v itself. However, the submicron magnetites lose a further 5-15% of their remanence when reheated through T-v. These irreversible changes in cycling across T-v, and the amounts of the changes, have potential value in determining submicron magnetite grain sizes. The irreversibility is mainly caused by 2D-->SD transformations on cooling through T-v, which preserve or enhance remanence, while SD-->2D transformations on warming through T-v cause remanence to demagnetize. (C) 2002 Elsevier Science B.V. All rights reserved.