多晶態鑭鍶錳氧磁譜在磁場下的特徵

Permeability Characterization of Polycrystalline La0.7Sr0.3MnO3 under Applied Magnetic Fields

本實驗製作 La0.7Sr0.3MnO3塊材，量測其磁導率與電阻率對溫度的關係，並探討在外加磁場下複數磁導率的變化行為。磁導率隨溫度升高顯現鐵磁到順磁的相轉變，電阻率隨溫度增高呈現對應的金屬到半導體相轉變。所量測到的磁譜皆具明顯色散行為，且顯現磁壁位移鬆弛特性。隨外加磁場增加，磁導率減少，磁壁位移鬆弛頻率𝒇𝒅𝒘𝒓 增加。磁導率對頻率的色散關係，可用多域內磁壁位移與單域內磁域旋轉兩項相加而得。由於樣品電阻率很小，渦電流阻滯為磁壁位移主要阻滯來源，𝒇𝒅𝒘𝒓 與相關公式計算出之數值相符。量測到的𝒇𝒅𝒘𝒓 數值，在 0 到 500 Oe 的外加磁場變化下，可從 380 kHz 變化到 980 kHz。

 

The polycrystalline La0.7Sr0.3MnO3 samples have been prepared to investigate the phase transition temperature and the permeability spectra under various applied magnetic fields. The temperature dependence of permeability shows the ferromagnetic to paramagnetic phase transition and the temperature dependence of resistivity shows the corresponding metal to semiconductor phase transition. All the measured spectra display pronounced dispersion with relaxation character due to the domain wall displacement. As the applied magnetic field increases, the permeability decreases and the domain-wall relaxation frequency 𝑓ௗ௪ ௥ increases. The measured spectra can be described by the sum of two relaxations, which are corresponding to the domain-wall displacements and the domain rotations, respectively. Since the resistivity of the samples is very small, the damping mainly originates from the eddy currents associated with the domain-wall displacement, and the measured 𝑓ௗ௪ ௥ are consistent with the value calculated from the correlated formula. As the applied magnetic field increases from 0 to 500 Oe, 𝑓ௗ௪ ௥ could increases from 380 kHz to 980 kHz.