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Posted: Jun 11, 2017
Superconducting ferromagnetic nanodiamond films
(Nanowerk News) Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. However, Synthetic-doped diamond can be not only superconducting but also ferromagnetic.
In ACS Nano ("Superconducting Ferromagnetic Nanodiamond"), an international team of researchers has now reported on the investigation of the interplay between ferromagnetism and electrical transport in hydrogenated and heavily boron-doped nanodiamond (HBD) films, which have a Curie temperature of TCurie > 400 K.
The authors write that, in spite of the presence of the ferromagnetic ordering, the superconducting state still
develops in their HBD films at Tc ∼ 3 K. The magnetization and resistivity data of the HBD demonstrate at different temperatures important correlations, suggesting spin-dependent electrical transport and possible Cooper pairing due to spin fluctuations in the HBD films.
They also point out that the significant magnetic remanence well above room temperature, the anomalous Hall effect, and the giant positive low-field magnetoresistance observed in these HBD films bring attention to the potential applications of this material in different areas, e.g., magnetoelectronics, spintronics, and magnetic field sensing.
"Most importantly" as the authors conclude, "the ferromagnetic ordering with TCurie > 400 K and the superconducting ordering with Tc ∼ 3 K, proven to be electronically entangled with each other, make our HBD also an interesting platform for investigating the competing interplay between the two antagonistic strongly correlated states of condensed matter."
"Our data indicate the presence of a precursor phase, in which spin fluctuations intervene and contribute to the superconducting transition at lower temperatures," they continue. "The significant difference between the starting temperature of this precursor phase (∼100 K) and Tc, however, raises an important question, i.e., how does a ferromagnetic superconductor such as our HBD 'foresee' its low-temperature superconducting 'fate' and start 'preparing' for the superconducting transition via antiferromagnetic arrangements of the magnetic domains at a much higher temperature?"
More thorough local measurements, i.e., mapping of the spin polarizations and the density of states in the precursor phase, and theoretical modeling are needed to solve this mysterious problem.