双层钙钛矿锰氧化物La1.2-xDyxSr1.8Mn2O7(x=0.00,0.05)的磁性和类Griffiths研究

Griffiths-like Phase and Magnetic Property of Layered Perovskite La1.2-xDyxSr1.8Mn2O7(x=0.00,0.05)

采用传统固相反应法制备多晶样品La1.2-xDyxSr1.8Mn2O7(x=0.00,0.05),通过测量样品的磁化强度与温度变化曲线(M-T)以及不同温度下磁化强度与外加磁场的变化曲线(M-H)对样品的磁性和类Griffiths相进行了研究.研究发现,两个样品分别在15-400 K的测量温度范围内,在类Griffiths相温度(TG≈368、360 K)以上处于纯顺磁态;在奈尔温度(TN≈210、183 K)-TG范围内,系统处于反铁磁-铁磁共存态,存在类Griffiths相,随温度的降低,样品的铁磁性逐渐增强;在TN以下,随温度的降低,铁磁性逐渐减弱,反铁磁性增强,样品呈现出了团簇玻璃行为.通过对比两个样品后发现,掺杂后样品x=0.05比未掺杂样品的磁性、三维长程居里温度(Tc3D)和类Griffiths相温度(TG)均降低,这是由于Dy3+离子半径比La3+离子半径小,掺杂之后导致晶格畸变所引起的.

Polycrystalline samples of double-layered manganite La1.2-xDyxSr1.8Mn2O7(x=0.00,0.05) with the perovskite structure were prepared by conventional solid-state reaction. By measuring the dependence of magnetization on temperature and also on magnetic field, the magnetic properties in the temperature range of 15-400 K were investigated. Above the Griffiths-like temperature TG(TG≈368 K and 360 K), the samples enter a pure paramagnetic state;In the temperature range TN-TG,the ferromagnetism gradually enhances with decreasing temperatures, where TN≈210 K and 183 K are the Neel temperature. Coexistence of ferromagnetic and paramagnetic characteristics is observed. At temperatures below TN, the antiferromagnetism enhances and the ferromagnetism reduces, and behavior like clustered spin glass appear. With the La3+ substituting by Dy3+, the magnetic properties, the long range 3 D ferromagnetism(FM) transition temperature and the Griffiths-like phase temperature decreasing. These effects are attributed to the lattice distortion due to the substitution of the smaller Dy3+.