Porwal Rajni, Gupta Anurag, Budhani R C
Academy of Scientific and Innovative Research, CSIR-National Physical Laboratory, New Delhi-110012, India. CSIR-National Physical Laboratory, New Delhi-110012, India.
J Phys Condens Matter. 2016 Dec 21;28(50):506003. doi: 10.1088/0953-8984/28/50/506003. Epub 2016 Oct 21.
The influence of YBaCuO (YBCO) superconductor layer (S-layer) with a varying thickness d = 20-50 nm on the magnetic coupling between two LaCaMnO (LCMO) ferromagnet layers (F-layer, thickness d = 50 nm) in F/S/F heterostructures (HSs) was investigated by measuring global magnetization (M) in a temperature (T) range = 2-300 K and a magnetic field (H) range = 0-10 kOe. All the HSs were superconducting with the critical temperature (T ) decreasing from = 78 to 36 K with decrease in d , whereas the ferromagnetic ordering temperature T = 250 K did not change much. Systematically measured M-H loops of all HSs at both T > T and T < T show three main results (a) the two step magnetic reversal above T converts into a four step reversal below T in HSs with d ⩾ 30 nm, (b) the magnitude and magnetic field corresponding to the additional two switching steps show characteristic evolution with T and d ; and (c) the HS with d = 20 nm shows radically different behaviour, where the two step magnetic reversal above T continues to persist below T and converts into a single step reversal at T [Formula: see text] T . The first two results indicate magnetostatic coupling between the magnetic domains and the vortices across the two F/S interfaces resulting in reversal dynamics different from that deep within the LCMO layers. Whereas, the result 'c' reveals indirect exchange coupling between LCMO layers through the superconducting YBCO layer, which is a clear experimental evidence of coexistence of ferromagnetism and superconductivity in nm scale F/S/F HSs expected theoretically by Sa de Melo (2003 Physica C 387 17-25).
通过在2 - 300 K的温度范围和0 - 10 kOe的磁场范围内测量全局磁化强度（M），研究了厚度d = 20 - 50 nm变化的钇钡铜氧（YBCO）超导层（S层）对铁磁/超导/铁磁（F/S/F）异质结构（HSs）中两个镧钙锰氧（LCMO）铁磁层（F层，厚度d = 50 nm）之间磁耦合的影响。所有的HSs都是超导的，其临界温度（Tc）随着d的减小从78 K降至36 K，而铁磁有序温度Tf = 250 K变化不大。在T > Tc和T < Tc时系统测量的所有HSs的M - H回线显示出三个主要结果：（a）在d⩾30 nm的HSs中，高于Tc时的两步磁反转在低于Tc时转变为四步反转；（b）与额外两个开关步骤对应的大小和磁场随T和d呈现出特征性演变；（c）d = 20 nm的HSs表现出截然不同的行为，高于Tc时的两步磁反转在低于Tc时持续存在，并在T [公式：见正文] Tc时转变为单步反转。前两个结果表明，跨越两个F/S界面的磁畴与涡旋之间存在静磁耦合，导致反转动力学不同于LCMO层内部深处的情况。而结果“c”揭示了LCMO层通过超导YBCO层的间接交换耦合，这是纳米尺度F/S/F HSs中铁磁性和超导性共存的明确实验证据，理论上由萨德·梅洛（2003年，《物理C》387卷，17 - 25页）所预期。
