Resonant spin tunneling in randomly oriented nanospheres of Mn 12 acetate

Under the terms of the Creative Commons Attribution license (3.0 Unported or 4.0 International).-- et al.We report measurements and theoretical analysis of resonant spin tunneling in randomly oriented nanospheres of a molecular magnet. Amorphous nanospheres of Mn 12 acetate have been fabricated and characterized by chemical, infrared, TEM, x-ray, and magnetic methods. Magnetic measurements have revealed sharp tunneling peaks in the field derivative of the magnetization that occur at the typical resonant field values for the Mn 12 acetate crystal in the field parallel to the easy axis. Theoretical analysis is provided that explains these observations. We argue that resonant spin tunneling in a molecular magnet can be established in a powder sample, without the need for a single crystal and without aligning the easy magnetization axes of the molecules. This is confirmed by reanalyzing the old data on a powdered sample of nonoriented micron-size crystals of Mn 12 acetate. Our findings can greatly simplify the selection of candidates for quantum spin tunneling among newly synthesized molecular magnets.The work at the University of Barcelona has been supported by Spanish Government Project No. MAT2011-23698. S.L. acknowledges financial support from the FPU Program of Ministerio de Educacion, Cultura, y Deporte of the Spanish Government. I.I. and J.E. thank the MINECO for the Ramon y Cajal contract and the FPI fellowship, respectively. The work of E.M.C. at Lehman College is supported by the US National Science Foundation through Grant No. DMR-1161571. S.J.L.B. was supported by DOE-BES under Contract No. DE-AC02-98CH10886.Peer reviewe