Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress‐controlled titanomagnetite (Fe2.4Ti0.6O4) particles—II. Rotational hysteresis losses
Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress‐controlled titanomagnetite (Fe2.4Ti0.6O4) particles—II. Rotational hysteresis losses
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DOI：
10.1046/j.1365-246x.1999.00853.x
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发表时间：
1999-08
影响因子：
2.8
通讯作者：
R. Keller;E. Schmidbauer
中科院分区：
文献类型：
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作者：
R. Keller;E. Schmidbauer
测量了研磨和蚀刻的合成2.4、12.5和165 mm钛磁铁矿（TM 60）颗粒的滞后参数作为温度的函数。结果表明，似乎是由微应力所决定的特性，所产生的高密度的位错和其他晶格缺陷，这是在尖晶石晶格中引入的研磨过程。结果表明：（1）2.4mm颗粒为单畴（SD），饱和剩磁比rs /s（20°C）为0.5，矫顽力Hc（20°C）为75 kAm 1，后者只能用应力诱导各向异性来解释，因为颗粒的形状和磁晶各向异性都太低。在高达~200°C的温度范围内，几乎与温度无关的矫顽力比H cr /H c #1.5高于具有单轴各向异性的Stoner-Wohlfarth SD颗粒的预期值;这种行为归因于晶格缺陷导致的不规则方向的微应力。相比之下，汉高图几乎显示了Stoner-Wohlfarth粒子的预期行为。由于研磨过程中的断裂过程，发生了部分低温氧化，导致居里温度T c#230 - 260°C提高，从饱和磁化强度数据推断。(2)12.5 mm颗粒（Tc =205°C）显示出典型的伪单畴（PSD）行为，其中s rs /s（20°C）为0.18，Hc（20°C）为11 kA m-1，这两个值都比多畴（MD）颗粒高得多，并且Hcr/Hc（20°C）为1.9。磁化过程似乎主要取决于可逆和不可逆的域旋转，也就是说，畴壁位移发挥次要作用，因为强钉扎力的畴壁在晶格缺陷。随着温度的升高，s rs /s s的下降相对较弱，因此PSD特性一直持续到居里点。Hc福尔斯随温度稳定下降到最小值Hc（160°C）# 4k A m-1;由于形成了某种SD区域，部分与微晶颗粒结构有关，因此Hc向200°C的进一步增加可能与整个颗粒的不均匀磁性行为有关;此外，热波动可能起作用。(3)165 mm颗粒（Tc =200°C）表现出MD行为，其中rs /s s（20°C）#0.025，Hc（20°C）#1k A m-1和Hcr/Hc（20°C）#8。当Hc在160°C以下随温度变化时显示出平滑的变化，Hcr/Hc福尔斯随温度下降到最小值Hcr/Hc（160°C）#2，并再次增加到Hcr/Hc（200°C）#4.5。
SUMMARY Hysteresis parameters as a function of temperature were measured for milled and etched synthetic 2.4, 12.5 and 165 mm titanomagnetite (TM60) particles. The results show characteristics that appear to be dictated by microstresses, generated by a high density of dislocations and other lattice defects, that were introduced in the spinel lattice by the milling procedure. The following features were found. (1) 2.4 mm particles are single domain (SD) with a saturation remanent magnetization ratio s rs /s s (20°C)#0.5 and coercive force H c (20°C)#75 kA m’1; the latter value can only be interpreted in terms of stress-induced anisotropy because shape and magnetocrystalline anisotropies are too low by far. The nearly temperature-independent coercivity ratio H cr /H c #1.5 up to ~200°C is higher than expected for Stoner‐Wohlfarth SD particles with uniaxial anisotropy; this behaviour is attributed to irregularly directed microstresses as a consequence of lattice defects. By contrast, a Henkel plot shows almost the behaviour expected for Stoner‐Wohlfarth particles. Due to fracturing processes during milling, partial low-temperature oxidation has taken place, resulting in an enhanced Curie temperature T c #230‐260°C, as extrapolated from data of saturation magnetization. (2) 12.5 mm particles (T c =205°C) show typical pseudo-single-domain (PSD) behaviour, with s rs /s s (20°C)#0.18, H c (20°C)#11 kA m’1, both values being much higher than for multidomain (MD) particles, and H cr /H c (20°C)#1.9. Magnetization processes appear to be dictated largely by reversible and irreversible domain rotations; that is, domain wall displacements play a minor role because of strong pinning forces for domain walls at lattice defects. As the temperature rises, a comparatively weak decrease in s rs /s s takes place, whence it follows that the PSD character persists up to the Curie point. H c falls with temperature steadily to a minimum of H c (160°C)# 4k A m’1; a further increase towards 200°C may be associated with an inhomogeneous magnetic behaviour throughout a particle because of the formation of some sort of SD regions, related in part to the microcrystalline particle structure; furthermore, thermal fluctuations may play a role. (3) 165 mm particles (T c =200°C) exhibit MD behaviour with s rs /s s (20°C)#0.025, H c (20°C)# 1k A m’1 and H cr /H c (20°C)#8. While H c shows a smooth variation with temperature up to 160°C, H cr /H c falls with temperature to a minimum H cr /H c (160°C)#2 and an increase occurs again to H cr /H c (200°C)#4.5.