Transition metal compounds with unquenched orbital magnetic moments.
Final Report Abstract
The orbital magnetic moment of Fe doped in Li 3N provides magnetic anisotropy strong enough to prevent spontaneous spin-flips on a time scale of hours and more. As a result, remnant magnetization emerges that is not driven by collective ordering phenomena or long-range interactions as in conventional ferromagnets. Spin-reversal at low temperatures is only possible via resonant quantum tunneling as unambiguously shown by our recent transverse-field measurements, which revealed strongly enhanced relaxation rates. Longitudinal fields, on the other hand, block the tunneling path and freeze the orientation of the magnetic moment. It came as a surprise when we realized that already 3 milliTesla are enough to fully suppress the quantum tunneling. Such a small field is easy to create and can be switched on or off almost instantaneously. Accordingly, it is possible to either freeze the magnetic moment or encourage it to flip in a specific direction. Detailed Moessbauer and X-ray absorption spectroscopy experiments revealed that the Fe atoms are indeed isolated and statistically distributed. This is a very important result since it rules out exotic cluster formations that could potentially allow for alternative explanations of the magnetic properties. It confirmed the model proposed earlier that is based on the smallest number of assumptions: the Fe moments present an atomic version of a magnetic bit. The simplicity of the system and even more so the comparatively high characteristic temperatures of 10 Kelvin make Fe-doped Li3N an ideal model system to study topological interference and quantum spin dynamics as well as possible applications in quantum computing and magnetic field sensing. A highlight among the results obtained on non-Fe substitutions is the observation of sharp resonance lines by high-field ESR and THz absorption in Co-doped Li3N; a giant zero-field splitting and an extraordinary large hyperfine structure were revealed and helped to gain a better understanding of the microscopic details behind the magnetic anisotropy of these systems. The presence of orbital moments in Fe-doped Li3N is not a coincidence and not a solitary case: based on the proposed structural motif of the “linear chain”, we have identified several other materials with similar properties: Fe-doped Li4SrN2, LiSr2[CoN2], (Sr6N) [FeN2][CN2]2, and K2NiO2. Furthermore, we have discovered a metallic electrical transport in Li2Sr[MnN]2, which is very rare in nitrides, and itinerant magnetic ordering close to room temperature. Ongoing investigations, in particular spectroscopic methods and inelastic neutron scattering, indicate a further improvement of our understanding of orbital moment formation in transition metals and quantum tunneling of the magnetization. The development of a novel crystal growth technique based on vapor transport of separated educts attracted considerable attention and was mentioned in several News articles (for example in Neue Züricher Zeitung, GIT Laboratory Journal, and Chemie.de). Our discovery of “Extreme Field Sensitivity of Magnetic Tunneling in Fe-doped Li3N” was published in Physical Review Letters and highlighted as an Editors’ Suggestion. Several news outlets, including popular science media, reported on our discovery. Our results obtained by synchrotron absorption measurements were covered in an article of the “Diamond Light Source - Science Highlights”.
Publications
- Single Crystal Growth and Anisotropic Magnetic Properties of Li2Sr[Li1-x FexN]2. Inorganics 4, 42 (2016)
P. Höhn, T. J. Ballé, M. Fix, Y. Prots & A. Jesche
(See online at https://doi.org/10.3390/inorganics4040042) - Avoided ferromagnetic quantum critical point: Antiferromagnetic ground state in substituted CeFePO. Phys. Status Solidi 254, 1600169 (2017)
A. Jesche, T. J. Ballé, K. Kliemt, C. Geibel, M. Brando & C. Krellner
(See online at https://doi.org/10.1002/pssb.201600169) - Spin-reversal energy barriers of 305 K for Fe2+ d6 ions with linear ligand coordination. Nanoscale 9, 10596 (2017)
L. Xu, Z. Zangeneh, R. Yadav, S. Avdoshenko, J. van den Brink, A. Jesche & L. Hozoi
(See online at https://doi.org/10.1039/c7nr03041j) - Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li3N. Phys. Rev. Lett. 120, 147202 (2018)
M. Fix, J. H. Atkinson, P. C. Canfield, E. del Barco & A. Jesche
(See online at https://doi.org/10.1103/physrevlett.120.147202) - Ferromagnetism vs. slow paramagnetic relaxation in Fe-doped Li3N. Phys. Rev. B 97, 064419 (2018)
M. Fix, A. Jesche, S. G. Jantz, S. A. Bräuninger, H.-H. Klauss, R. S. Manna, I. M. Pietsch, H. A. Höppe & P. C. Canfield
(See online at https://doi.org/10.1103/physrevb.97.064419) - Iron single crystal growth from a lithium-rich melt. J. Cryst. Growth 486, 50 (2018)
M. Fix, H. Schumann, S. G. Jantz, F. Breitner, A. Leineweber & A. Jesche
(See online at https://doi.org/10.1016/j.jcrysgro.2018.01.010) - Ferromagnetic ordering of linearly coordinated Co ions in LiSr2[CoN2]. Phys. Rev. B 99, 094422 (2019)
T. J. Ballé, Z. Zangeneh, L. Hozoi, A. Jesche & P. Höhn
(See online at https://doi.org/10.1103/physrevb.99.094422) - Electron Doping of the Iron-Arsenide Superconductor CeFeAsO Controlled by Hydrostatic Pressure. Phys. Rev. Lett. 125, 207001 (2020)
K. Mydeen, A. Jesche, K. Meier-Kirchner, U. Schwarz, C. Geibel, H. Rosner & M. Nicklas
(See online at https://doi.org/10.1103/physrevlett.125.207001) - Magnetic Field tuning of low energy spin dynamics in the single-atomic magnet Li2(Li1−xFex)N. Phys. Rev. B 102, 054426 (2020)
S. A. Braeuninger, A. Jesche, S. Kamusella, F. Seewald, M. Fix, R. Sarkar, A. A. Zvyagin & H.-H. Klauss
(See online at https://doi.org/10.1103/physrevb.102.054426) - Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy. Chem. Sci. 11, 11801 (2020)
M. S. Huzan, M. Fix, M. Aramini, P. Bencok, J. F. W. Mosselmans, S. Hayama, F. A. Breitner, L. B. Gee, C. J. Titus, M.-A. Arrio, A. Jesche & M. L. Baker
(See online at https://doi.org/10.1039/d0sc03787g) - Li2Sr[MnN]2: A magnetically ordered metallic nitride. Phys. Rev. Materials 5, 084407 (2021)
F. Hirschberger, T. J. Ballé, C. Haas, W. Scherer, A. A. Tsirlin, Yu. Prots, P. Höhn & A. Jesche
(See online at https://doi.org/10.1103/physrevmaterials.5.084407) - Terahertz Magneto-Optical Excitations of the sd-Hybrid States of Lithium Nitridocobaltate Li2(Li1–xCox)N. Inorg. Chem. 60, 4497 (2021)
C. Albert, T. J. Ballé, F. A. Breitner, Y. Krupskaya, A. Alfonsov, Z. Zangeneh, S. Avdoshenko, M. S. Eldeeb, L. Hozoi, A. Vilangottunjalil, E. Haubold, A. Charnukha, B. Büchner, A. Jesche & V. Kataev
(See online at https://doi.org/10.1021/acs.inorgchem.0c03358)
