CrO2薄膜的磁阻與磁性測量

Abstract

本實驗以鈦酸鍶（SrTiO3）、鋁酸鑭（LaAlO3）和矽（Si）為基板先利用直流濺鍍法成長TiO2薄膜做為緩衝層，然後在緩衝層上以化學氣相沈積法成功地長出具方向性的CrO2薄膜，由於TiO2緩衝層的影響，CrO2薄膜明顯呈現顆粒狀，而有負磁阻行為，在溫度5 K磁場5 Tesla時其磁阻大約15％∼18％之間。我們分別在膜面的平行與垂直方向加一磁場量測電阻與溫度的關係。分別在高溫與低溫時穩定在同一溫度下測量磁場與電阻的關係。我們也做了磁化強度與磁場的關係，我們很清楚的看到了難磁化方向與易磁化方向。綜合這些磁阻以及磁化強度的量測，透過量測數據整理與分析，結果發現CrO2薄膜在低磁場的負磁阻與磁場平行或垂直膜面有高度相關，而由頑磁力與磁阻的關係，可證實磁阻的來源是由於CrO2偏極化載子受到磁疇磁化排列規則性的影響所引起的。

We used TiO2 as the buffer layer to fabrication of the CrO2 thin film. TiO2 thin films were deposited on SrTiO3, LaAlO3 and Si subtrates by DC sputtering, then we successful fabricate the CrO2 thin film on the buffer layer with well defined orientation. The structure of CrO2 thin film were grainlar. These CrO2 thin film show large magnetoresistance. For T=5K with H=5 Tesla, the magnetoresistance of these CrO2 thin film were between 15%~18%. We applied the magnetic field parallel and perpendicular to the CrO2 thin film and measure the magnetization with applied field along the easy or hard axis. By those measurements we fined the magnetoresistance of CrO2 thin film strongly depends on the magnetic field parallel or perpendicular to the CrO2 thin film at low magnetic fields, while shows no direction dependence at high magnetic fields. From the coercivity and magnetoresistance, we can suggest that the source of magnetoresistance were related to the carrier’s spin polarization in CrO2 thin film and magnetic domains.