Magnetotransport and magnetic properties of amorphous $$\mathrm{NdNi}_5$$ thin films

Abstract

NdNi 5 is an intermetallic compound with a bulk Curie temperature (T Curie) of 6-13 K. While existing studies have focused on NdNi 5 crystals, amorphous thin-films of NdNi 5 are potentially important since they would be magnetically soft without magnetocrystalline anisotropy, meaning that small external magnetic fields could reverse the direction of their magnetization. Here, we report NdNi 5 thin-films with a thickness in the 5-200 nm range, deposited by DC magnetron sputtering onto Si(100). Films are amorphous with a weak temperature-dependent resistivity with values ranging between 150 and 300 µ cm. By means of noise spectroscopy, by analyzing the time-dependence of fluctuationinduced voltages, it is found that at low temperatures the resistance fluctuations are due to the Kondo effect. Volume magnetometry indicates T Curie = 70 K with a magnetic coercive field of 30 mT at 5 K for a 125-nm-thick film. The results are promising for the development of Ferromagnet(F)/ Superconductor(S)/Ferromagnet(F) pseudo spin-valve devices based on amorphous NdNi 5 thin films. Spintronics is a major field of research in condensed matter physics 1. The capability to create and manipulate electronic spin currents enables to realize spin-based devices which, compared to their traditional charge-based counterpart, can be faster and demand lower power 1. The birth of spintronics traces back to the discovery of giant magnetoresistance (GMR) in Fe/Cr synthetic antiferromagnetic multilayers in which the electrical resistance increases when the magnetization in the magnetic layers changes from a parallel to an antiparallel alignment 2,3. A large number of material systems have been proposed for spintronics 4 including superconductors in conjunction with magnetic materials. This has paved the way for superconducting spintronics, which has potential to lead to the development of circuits that are more energy efficient, meaning that they should generate less heat and require low power for their functioning 5,6. In particular, a ferromagnet with a small value of the coercive field, H c , can be easily tuned in its magnetic properties, going from a state in which the magnetization, M, is zero when the applied external magnetic field H is equal to H c to a state in which, for H > H c , M = 0. In superconducting/ ferromagnetic (S/F) systems, this property can push the S/F system from the normal to superconducting state at low temperatures. Such a system can be used as a superconducting valve, since it can be switched between a superconducting (ON) and a normal (OFF) state by controlling the value of H. NdNi 5 is an intermetallic compound belonging to the RENi 5 (RE = Rare-earth) series. In bulk form, it is characterized by a large magnetocrystalline anisotropy, with the easy (hard) axis lying along the a axis within the hexagonal plane (the c axis) and an a axis (c axis) magnetization at 35 T of 3.3 μ B /f.u. (1.65 μ B /f.u.) 7,8 , and a T Curie in the range of 6-13 K 8-11. Here μ B is the Bohr magneton. In order to be used in conjunction wit...

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