Antiferromagnet Spintronics

Spintronics is an important area of modern condensed matter physics which has led to new means for reading, writing and storing information. Magnetic tunnel junctions (MTJs) used in modern hard-drive read heads and magnetic random access memories comprise two ferromagnetic electrodes whose relative magnetization orientations can be switched between parallel and antiparallel configurations, yielding to two different memory states via the magnetoresistance effect. In spintronics, ferromagnets play, at the moment, an undismissable role, but from the applications perspective, it is particularly appealing the introduction of antiferromagnetic memory elements insensitive to external magnetic fields [1, 2].

Our research is devoted to the fabrication of antiferromagnetic tunnel junctions (ATJs) and devices based on the anisotropic magneto-resistance (AMR) effect, acting as electrically readable memories where the information is stored in antiferromagnetic materials (AFM). In comparison with ferromagnets, antiferromagnetically ordered components produce zero stray field and are more robust against magnetic field perturbations, thus allowing for larger packaging density ad higher reliability and durability. Indeed in ATJs metastable states corresponding to different spin configurations of the AFM can be set by cooling the sample and crossing the Néel temperature in external magnetic fields of different orientations. These metastable states can be detected electrically due to the AFM tunneling anisotropic magnetoresistance (TAMR) [2].

Current research activity is devoted to

  1. realizing IrMn-based ATJs on Silicon platforms, looking for CMOS compatibility, with operation temperature larger or equal than room temperature
  2. exploring the AFM properties of Chromium thin films, looking for the possibility of a magneto-electric control via proximity with a ferroelectric material (e.g. BaTiO3).

In parallel, ab-initio calculations in collaboration with the SPIN-CNR unit of L’Aquila (S. Picozzi) will address alternative ways of information writing (magnetoelectric coupling), as well as novel materials (Mn2Au, Cr, manganites), in order to propose new pathways to be followed and experimentally investigated.

Antiferromagnet Spintronics

Prototypical AFM-based memory device: (a) heterostructure stack; (b) working principle. The device is heated above its Néel temperature (TN) and then cooled down with applied magnetic field, either in the out-of-plane (HZ) or in-plane (HX) direction. The resulting TAMR (Tunneling Anisotropic Magneto-Resistance, defined as the percentage variation of the resistance after field cooling with HZ or HX) is 8% at 25 K.

References

[1] [doi] P. Wadley, V. Novak, R. P. Campion, C. Rinaldi, X. Marti, H. Reichlova, J. Zelezny, J. Gazquez, M. A. Roldan, M. Varela, D. Khalyavin, S. Langridge, D. Kriegner, F. Maca, J. Masek, R. Bertacco, V. Holy, A. W. Rushforth, K. W. Edmonds, B. L. Gallagher, C. T. Foxon, J. Wunderlich, and T. Jungwirth, “Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs,” Nat. Commun., vol. 4, p. 1–6, 2013.
[Bibtex]
@Article{Wadley2013,
Title = {Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs},
Author = {Wadley, P. and Novak, V. and Campion, R.P. and Rinaldi, C. and Marti, X. and Reichlova, H. and Zelezny, J. and Gazquez, J. and Roldan, M.A. and Varela, M. and Khalyavin, D. and Langridge, S. and Kriegner, D. and Maca, F. and Masek, J. and Bertacco, R. and Holy, V. and Rushforth, A.W. and Edmonds, K.W. and Gallagher, B.L. and Foxon, C.T. and Wunderlich, J. and Jungwirth, T.},
Journal = {Nat. Commun.},
Year = {2013},
Month = aug,
Pages = {1--6},
Volume = {4},
__markedentry = {[User:1]},
Comment = {Supplementary information available for this article at http://www.nature.com/ncomms/2013/130820/ncomms3322/suppinfo/ncomms3322_S1.html},
Doi = {10.1038/ncomms3322},
File = {:.\\2013\\[NatComm_Wadley] Tetragonal phase of epitaxial room-temperature antiferromagnetic CuMnAs.pdf:PDF},
Owner = {christian},
Publisher = {Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.},
Timestamp = {2013.10.20},
Url = {http://dx.doi.org/10.1038/ncomms3322}
}
[2] [doi] D. Petti, E. Albisetti, H. Reichlová, J. Gazquez, M. Varela, M. Molina-Ruiz, A. F. Lopeandía, K. Olejník, V. Novák, I. Fina, B. Dkhil, J. Hayakawa, X. Marti, J. Wunderlich, T. Jungwirth, and R. Bertacco, “Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling,” Applied Physics Letters, vol. 102, iss. 19, 2013.
[Bibtex]
@Article{Petti2013,
Title = {{Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling}},
Author = {Petti, D. and Albisetti, E. and Reichlová, H. and Gazquez, J. and Varela, M. and Molina-Ruiz, M. and Lopeandía, A.F. and Olejník, K. and Novák, V. and Fina, I. and Dkhil, B. and Hayakawa, J. and Marti, X. and Wunderlich, J. and Jungwirth, T. and Bertacco, R.},
Journal = {Applied Physics Letters},
Year = {2013},
Number = {19},
Volume = {102},
Art_number = {192404},
Document_type = {Article},
Doi = {10.1063/1.4804429},
Source = {Scopus},
Url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84877978965&partnerID=40&md5=eba32cb7c2eb230148bb16af9680576e}
}

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