| 摘要: | 我們透過固態反應法合成一系列的YBa(Cu1-xFex)2O5，藉此研究銅、鐵的比例對樣品的結構與磁性所產生的影響。根據磁化率的量測結果，我們得知在銅鐵比例相同的條件下此樣品具有兩個反鐵磁相變溫度(TN1 和 TN2)；同時，中子繞射的結果顯示在這兩個相變點附近會發生磁結構的相變(正配相→非正配相)，在溫度較低的情況下正配相非常微弱。然而，隨著鐵的化學劑量越高第二相變溫度TN2也跟著升高，此相變只發生在0.490 ≤ x ≤ 0.515的範圍之內，無論是磁化率量測以及中子繞射都得到相同的結果。唯一不同的是當0.510 ≥ x時，鐵的參雜會誕生出新的磁結構相變取代了原有的正配-非正配相變，並與原有的正配相共存。
Structural and magnetic properties of variety Cu/Fe ratio of the double perovskite YBa(Cu1-xFex)2O5 were investigated by using neutron powder diffraction (NPD) and magnetization measurements. The crystal structures of all the samples are formed in a space group of P4/mmm with in the x range between 0.45 and 0.55. Susceptibility measurements of YBaCuFeO5 exhibited two antiferromagnetic transitions at TN1 ~ 450 K and TN2 ~ 175 K, accompanied with two anomalous spin ordering. The refinement results show an antiferromagnetic commensurate (CM) phase with propagation vector Qc1=(1/2,1/2,1/2), between TN1 and TN2, which as a collinear magnetic structure.
Below TN2, two satellite incommensurate (ICM) magnetic reflections were observed at around each commensurate ones with Qi=(1/2,1/2,1/2+-q), indicating the appearance of spiral magnetic structure. Furthermore, these observations revealed that TN2 is very sensitive to the concentration of Fe, and explained the paradox of transition temperatures in the past reports. For x ≥ 0.510, extra magnetic reflections emerge with a propagation wavevector Qc2=(1/2,1/2,0), suggesting the coexistence of two commensurate magnetic phases with propagation wavevectors of (1/2,1/2,1/2) and (1/2,1/2,0), respectively. |
