Material Sciences
Vol.05 No.03(2015), Article ID:15189,6 pages
10.12677/MS.2015.53008

An Investigation on Magnetic Anisotropy Induced in Fe-Based Ribbons during Current Stress Annealing

Jing Zhao1, Yunzhang Fang1,2*, Xingwei He1, Fei Xiao1, Ming Chen1, Fanxue Meng1, Xiaohong Yang3, Rimin Pan1

1College of Mathematics, Physics and Information Engineering, Zhejiang Normal University, Jinhua Zhejiang

2Zhejiang Province Key Laboratory of Solid State Photoelectric Device, Jinhua Zhejiang

3Jinhua Polytechnic, Jinhua Zhejiang

*通讯作者。

Email: zhaojing_5733@126.com, *fyz@zjnu.com

Received: Apr. 11th, 2015; accepted: May 4th, 2015; published: May 8th, 2015

Copyright © 2015 by authors and Hans Publishers Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

ABSTRACT

The mechanism of stress induced magnetic anisotropy is an important basic science problem which has been investigated extensively; currently, disputes still exist in the understanding about the mechanism of stress induced magnetic anisotropy. This paper studies the dynamic process that Fe73.5Cu1Nb3Si13.5B9 alloy ribbon (Fe-based alloy ribbon) prepared with single roll faster quenching is under the effect of stress that current annealing (current stress annealing ) induced magnetic anisotropy. We design a device which can monitor in-situ the length variation of Fe- based alloy ribbon during current stress annealing process and give a tracking measurement. The magnetic anisotropy field is obtained by the longitudinal curve of giant magneto-impedance. Analyze stress induced magnetic anisotropy field and the relationship between the thin belt elongation and annealing current, we know, under the action of applied stress 50 MPa, the annealing current density J = 45 A/mm2 is the critical point of ribbon creep. When the annealing current is less than the creep point, the anisotropy is not obvious; when greater than the point, the current stress annealing induced magnetic anisotropy field changes quickly, and the field increases linearly with the increase of the annealing current density.

Keywords:Current Annealing, Stress, Creep, Magnetic Anisotropy

FeCuNbSiB合金薄带电流应力退火感生磁各向异性的研究

赵 静1,方允樟1,2*,何兴伟1,肖 飞1,陈 明1,孟繁雪1,杨晓红3,潘日敏1

1浙江师范大学数理与信息工程学院,浙江 金华

2浙江省固态光电器件重点实验室,浙江 金华

3金华职业技术学院,浙江 金华

Email: zhaojing_5733@126.com, *fyz@zjnu.com

收稿日期:2015年4月11日;录用日期:2015年5月4日;发布日期:2015年5月8日

摘 要

应力感生磁各向异性机理是一项备受关注的重要基础科学问题,本文采用电流应力退火原位观测装置,监测FeCuNbSiB合金薄带在应力作用下电流退火过程中薄带的伸长量,由纵向驱动巨磁阻抗效应曲线得到薄带应力退火感生的磁各向异性场。分析比较应力电流退火感生磁各向异性场与退火电流及薄带伸长量之间的关系获知,在50 MPa外加应力作用下,退火电流密度J = 45 A/mm2为薄带蠕变的临界点,在退火电流小于蠕变点时,电流应力退火没有感生明显的磁各向异性场,在退火电流大于蠕变点时,电流应力退火感生的磁各向异性场迅速变大,且随退火电流密度的增加呈线性增大。

关键词 :电流退火,应力,蠕变,磁各向异性

1. 引言

自从Yoshizawa [1] 报道纳米晶软磁材料以来,Fe基纳米晶薄带因其优异的软磁性能,得到了广泛应用。为了满足不同应用需求,需要对薄带的磁结构和磁性能进行调控,磁场退火[2] [3] 和应力退火[4] [5] 是常用的磁结构和磁性能调控手段。已有研究结果表明,应力退火感生的磁各向异性要远大于磁场退火 [2] - [7] ,被认为是一种最具应用前景的磁结构调控技术,备受关注。但是人们对于应力退火感生磁各向异性的机理的认识还存在颇多争议 [6] [8] - [10] 。Herzer等 [6] [11] 的实验结果表明,经张应力退火的Fe基纳米晶薄带具有明显的伸长量。因此,他认为非晶基底的滞弹性形变并对a-Fe(Si)晶粒造成内部的拉应力,而a-Fe(Si)晶粒具有负的磁致伸缩系数,与内部拉应力耦合发生磁弹耦合作用。这种磁弹耦合作用是应力退火感生磁各向异性的原因。近年来,Ohuma等 [8] [12] - [14] 采用透射XRD技术研究经应力退火样品发现,应力退火感生晶格各向异性,他认为晶格各向异性是感生磁各向异性的直接证据。已有的研究,主要是关注同一温度退火不同应力作用下所感生磁的各向异性的变化情况,即主要关注应力作用因素。另外,由于受技术手段限制,人们通常采用静态测量退火前后样品特性的方法探究应力退火感生磁各向异性的规律和机理,很少采用原位测量的方法。再者,电流退火工艺相比温度退火工艺可以更精准地控制退火过程感生的磁结构,同时具有节约退火过程能耗的效果,但是有关电流应力退火的研究鲜有报道。本文采用原位观测电流加应力退火过程的方法研究同一应力作用下不同电流退火感生磁各向异性规律,研究结果对于非晶软磁合金薄带的磁结构调控技术研发具有参考价值。

2. 实验

电流退火是将持续的电流通过非晶样品,利用电流产生的焦耳热使样品晶化的过程。电流应力退火,即将退火电流通过非晶样品进行退火的同时对被退火样品施加外应力,对样品磁结构进行调控的技术。应力退火装置如图1所示,夹具一端固定,另一端可以在光滑的滑轨上移动。在滑块的外端连接细绳,通过一个定滑轮后悬挂砝码,这样样品就受到一个沿薄带轴向的张应力作用,张应力的大小可以通过增减砝码的质量进行改变。外加张应力的计算公式为:

(1)

其中m为所挂砝码质量,,s是薄带的横截面积。夹具用单面导电的材料做成,夹带子的一面导电,另一面绝缘。将导线连接在夹头上,这样夹上非晶带子就可以导通。

单棍快淬法制备Fe73.5Cu1Nb3Si13.5B9非晶薄带,宽0.5 mm,厚25 μm,截取长15 cm的薄带,调整夹具两端的距离,使两夹具之间的薄带长度为10 cm,即有效长度,之后提到的薄带长度均为有效长度。电流I由串接在退火回路中的电流表读取。通过退火样品的电流密度:

(2)

I是电表读数,单位A,s是薄带横截面积,单位mm2。应力与电流密度的计算均以退火前非晶薄带的尺寸为准。电流应力退火过程中,用显微摄像头全程拍摄薄带滑移端的刻度,刻度精度为0.1 mm。

本实验主要讨论电流应力退火感生的磁各向异性,根据杨燮龙等人 [15] 定义:横向磁各向异性场(HK)等于纵向驱动巨磁阻抗曲线下降沿斜率变化最大处的外加磁场。图2是纵向驱动巨磁阻抗测试原理示意图所示,定义纵向驱动GMI巨磁阻抗效应比如下:

(3)

式中分别是在任意外磁场和最大外磁场下测得的阻抗值。关于磁各向异性场HK

(4)

H+与H的取值如图3所示,取半高宽对应的磁场为下降沿斜率变化最大处。

3. 实验结果与讨论

图4是在薄带轴向外加50 MPa应力作用下,退火电流由0增加到60 A/mm2过程薄带伸长率δ与退火电流密度平方的关系曲线。薄带伸长率定义为:

Figure 1. The schematic diagram of current stress annealing device

Figure 2. The longitudinal drive GMI test schematic diagram

Figure 3. FeCuNbSiB GMI curve after annealing and anisotropy field calculation principle

图3. FeCuNbSiB退火后GMI曲线图及各向异性场计算原理

Figure 4. The relationship of ribbon elongation δ and the Annealing current density square J2

图4. 薄带伸长率δ与退火电流密度平方J2的关系

Figure 5. The relationship of magnetic anisotropy field and annealing current

图5. 磁各向异性场与退火电流关系曲线

分析以上实验数据可知,当加应力50 MPa退火时,J = 45 A/mm2为转折点,电流密度小于这个转折点时。薄带伸长率与电流密度的平方成正比,根据焦耳定律,电流密度的平方正比于导体的发热量。在同等散热条件和热容量不变的情况下,导体的发热量正比于温度。即可以将退火电流密度平方变化近似视为被退火样品的温度变化。则在退火电流密度小于J = 45 A/mm2时,薄带长度随退火电流增加而伸长的现象属于线性热膨胀。当退火电流密度大于J = 45 A/mm2时,不满足线性关系,此时薄带开始蠕变。且J = 45 A/mm2也是磁各向异性场的分界点,电流密度小于这个分界点时,磁各向异性场变化不大;电流密度大于这个分界点时,磁各向异性场变化明显,呈线性增加。这说明薄带开始蠕变时,磁各向异性场才开始明显被感生。

Figure 6. The relationship between ultimate elongation of the ribbon and the magnetic anisotropy field

图6. 薄带最终伸长率与磁各向异性场关系图

4. 结论

本文通过对Fe73.5Cu1Nb3Si13.5B9非晶薄带电流应力退火过程伸长量的原位监测以及经过不同电流密度退火感生的磁各向异性的测量,得到J = 45 A/mm2为此材料的蠕变点,当薄带开始蠕变时,感生的磁各向异性场快速增大,与退火电流呈线性关系。因此,本文的实验结论可运用到实际的退火工艺中,找出蠕变点,再根据所需要的磁各向异性场进行退火,将取得事半功倍的效果。

基金项目

国家重点基础研究发展计划(973计划) (批准号:KYZKJY12107);浙江省自然科学基金(批准号:Y14A040014)。

文章引用

赵 静,方允樟,何兴伟,肖 飞,陈 明,孟繁雪,杨晓红,潘日敏, (2015) FeCuNbSiB合金薄带电流应力退火感生磁各向异性的研究
An Investigation on Magnetic Anisotropy Induced in Fe-Based Ribbons during Current Stress Annealing. 材料科学,03,55-61. doi: 10.12677/MS.2015.53008

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