Patra M, Thakur M, Majumdar S, Giri S
Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India. Center for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
J Phys Condens Matter. 2009 Jun 10;21(23):236004. doi: 10.1088/0953-8984/21/23/236004. Epub 2009 May 7.
We report new results for the exchange bias effect in Nd(1-x)Sr(x)CoO(3) for x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state in a spontaneously phase separated system. The zero-field-cooled magnetization exhibits FI (T(FI)) and ferromagnetic (FM; T(C)) transitions at ∼23 and ∼70 K, respectively, for x = 0.20. Negative horizontal and positive vertical shifts of the magnetic hysteresis loops are observed when the system is cooled through T(FI) in a positive static magnetic field. A training effect is observed for x = 0.20, which could be interpreted satisfactorily by the spin configurational relaxation model. The unidirectional shifts of the hysteresis loops as a function of temperature exhibit an absence of exchange bias above T(FI) for x = 0.20. Analysis of the cooling field dependence of the exchange bias field and magnetization indicates that the FM clusters consist of a single magnetic domain with an average size of around ∼20 and ∼40 Å for x = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold for x = 0.20; these grow and coalesce to form the bigger size for x = 0.40 resulting in a weak exchange bias effect.
我们报告了在(x = 0.20)和(0.40)的(Nd(1 - x)Sr(x)CoO(3))中交换偏置效应的新结果，其中交换偏置现象与自发相分离系统中的亚铁磁（FI）态有关。对于(x = 0.20)，零场冷却磁化强度分别在约(23)和约(70K)处呈现FI（(T(FI))）和铁磁（FM；(T(C))）转变。当系统在正静态磁场中冷却通过(T(FI))时，观察到磁滞回线的负水平和正垂直偏移。对于(x = 0.20)观察到了训练效应，这可以通过自旋构型弛豫模型得到令人满意的解释。对于(x = 0.20)，磁滞回线的单向偏移作为温度的函数在(T(FI))以上不存在交换偏置。对交换偏置场和磁化强度的冷却场依赖性分析表明，对于(x = 0.20)和(0.40)，FM团簇分别由平均尺寸约为(20)和(40\mathring{A})的单个磁畴组成。对于(x = 0.20)，FM团簇的尺寸接近渗流阈值；对于(x = 0.40)，这些团簇生长并合并形成更大的尺寸，导致弱交换偏置效应。
