中文摘要：

采用传统的高温固相反应法,制备了钙钛矿锰氧化物（La0.975 Gd0.025）4/3 Sr5/3 Mn2 O 7多晶样品,利用X 射线衍射（XRD）仪、物性测量系统（PPMS）和超导量子磁强计（SQUID）研究了样品的结构、磁性和电性,结果表明：该多晶样品为 Sr3 Ti2 O 7型四方结构,空间群为 I4/mmm；样品的三维铁磁有序转变温度 T 3DC 和二维铁磁有序转变温度 T 2DC 分别为110 K 和240 K,在居里温度（T 3DC ）附近出现明显的磁熵变,当外磁场为2.5 T 时,其磁熵变值为3.1 J/kg＆#183;K；电性测量结果显示,T 3DC 也是样品经历金属性到绝缘性转变的温度,当 T 3DC ＆lt;T ＆lt;300 K时,样品遵循三维变程跳跃的导电方式,说明样品中载流子的输运过程是由磁不均匀性决定的.

英文摘要：

（La0.9 7 5 Gd0.02 5 ）4/3 Sr5/3 Mn2 O 7 polycrystalline sample was prepared by traditional solid state reaction method and structure,magnetic and electrical properties were investigated by measuring the M-T curve,M-H curve and R -T curve.Experimental results suggest the sample structure is Sr3 Ti2 O 7-type and its space group was I4/mmm.It transform from the two-dimensional short-range ferromagnetic order at T 2 D C to the three-dimensional long-range ferromagnetic state T 3 D C .In addition,the magnetic entropy change under 2.5 T magnetic field is up to 3.1 J/（kg＆#183;K）,which occurred near the Curie temperature.It can be seen from the fitted R-T curves that the electron conducting mechanism in the temperature range of 1 10 K＆lt;T ＆lt;300 K is in accordance with three dimensional variable range hopping conduction.