燒結時間對鑭鍶錳氧複數磁導率的影響

Influence of Sintering Time on Complex Permeability for Polycrystalline La0.7Sr0.3MnO3 Manganite

因具有在低磁場下的巨磁阻抗(GMI)效應，鈣鈦礦結構的錳氧化物鑭鍶錳氧(LSMO)近年來成為製作射頻微波元件與磁量計可選用的材料之一。由於LSMO 的GMI 效應與複數磁導率在磁場下的變化行為有關，吾人製作不同燒結時間的樣品，探討在外加磁場下LSMO 複數磁導率的行為。研究結果顯示，增加燒結時間雖然可提升樣品的磁導率，卻會因磁滯損耗與渦電流損耗而造成品質因子下降。當外加直流磁場時，樣品磁導率急遽減少。8 小時，16 小時與24 小時燒結的樣品，在450 G 的外加磁場下，複數磁導率實部變化率在50 kHz，40 kHz 與30 kHz 顯現-84%，-86%與-85%的極大數值，複數磁導率虛部變化率在260 kHz，260 kHz 與160 kHz 顯現-94%，-94%與-93%的極大數值。外加磁場也會造成共振頻率fr 增加，當磁場大於50 G 時，fr會隨磁場線性增加，這個特性可應用於製作LSMO 磁量計。

Recently, peroviskite manganite La0.7Sr0.3MnO3 (LSMO) has spurred lots of research excitement due to the exhibition of low-field giant magnetoimpedance (GMI) effect. Since the GMI effect for mangnites originates mainly from the magnetic-field-induced change of complex permeability, we have fabricated LSMO toroidal inductors with different sintering time to investigate the field-induced behavior of complex permeability. All the measured spectra show relaxation character due to domain wall displacement. As the sintering time increases, the permeability increases; however, the resonance frequency fr and quality factor (Q factor) decreases. Under applied magnetic field Bdc, the permeability decreases. A giant field-induced change ratio of the real part for complex permeability Dμ′/μ′ of -84%, -86% and -85% at 50 kHz, 40 kHz and 30 kHz are obtained under a very small field Bdc = 450 G for the 8 hr, 16 hr and 24 hr sintering samples. Besides, a huge field-induced change ratio of the imaginary part for complex permeability Dμ′′/μ′′ of -94%, -94% and -93% at 260 kHz, 260 kHz and 160 kHz are found under Bdc = 450 G for the 8 hr, 16 hr and 24 hr sintering samples. The value of fr increases with Bdc and a linearly dependence between fr and Bdc is observed above 50 G. Our measured results are useful in understanding the GMI behavior of LSMO manganites and fabrication of LSMO magnetometers.