多层锰氧化物Ba_(6-x)Sr_xMn_5O_(16)(x=0,0.5,1.0,1.5)材料的制备和磁性研究

Preparation and Magnetic Properties of Multilayered Manganite Ba_(6- x)Sr_xMn_5O_(16)( x =0,0. 5,1. 0,1. 5)

通过传统的固相反应法制备了多层钙钛矿锰氧化物Ba_(6-x)Sr_xMn_5O_(16)(x=0,0.5,1.0,1.5)系列单相样品,比较详细地分析了样品的结构和磁性变化规律。通过室温X射线衍射(XRD)测试,样品为纯的单相n=5的Ruddlesden-Popper型钙钛矿结构,具有四方结构的Cmca(No.64)空间群。采用超导量子磁强计(SQUID)对该系列样品的磁性进行了研究。通过采用超导量子磁强计(SQUID)测量样品Ba6Mn5O16的磁化强度随温度变化曲线得出:由于低温强的三维反铁磁耦合,当温度低于75 K时,零场冷却(ZFC)和带场冷却(FC)曲线几乎重合。当温度达到奈尔温度TN(≈150 K)时,三维的反铁磁耦合完全被破坏,曲线的特征有一个明显的大鼓包。在温度低于50 K时,观察到居里尾(Curie tail)。随着Sr离子替代Ba离子量的增加,TN逐渐降低。样品在TN附近有很宽的转化峰,很可能存在三维反铁磁耦合到二维反铁磁耦合再到顺磁的连续变化过程。

Perovskite-type muhilayered manganates of Ba6-xSrxMn5 O16 （X = 0, 0. 5, 1.0, 1.5 ） were prepared by traditional solidstate reaction method. A more detailed analysis of the structure and magnetic variation of the samples was then carried out. X-ray diffraction （XRD） results indicated that the samples were a pure single-phase n = 5 Ruddlesden-Popper perovskite structure and had a tetragonal structure with space group Cmca （ No. 64）. Through analyzing the magnetization curve of Ba6 Mn5 O16 changing with temperature measured by a superconducting quantum interference device magnetometer （SQUID）, it was found that owing to low temperature and strong three-dimensional antiferromagnetic coupling, when the temperature was below 75 K, zero field cooling （ZFC） and field cooling （FC） curves almost coincided. Pyromagnetic curves of maternal sample Ba6Mn3O16 showed an obvious big bulge at about Neel temperature TN （ ≈150 K） , implying that crystals occurred strongly antiferromagnetic coupling. With the concentration of Sr2＋ substituting for Ba2＋ increasing, TN （ ≈ 150 K） gradually decreased. The samples exhibited a successive transition process, which was from three dimensional antiferromagnetic coupling to two dimensional antiferromagnetic coupling, and finally to pmamagnetism. When the temperature was lower than 50 K, Curie tail was observed.