Brannon B. Klopfer

Publications (2)14.79 Total impact

• Article: Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures

  Beena Kalisky, Julie A. Bert, Brannon B. Klopfer, Christopher Bell, Hiroki K. Sato, Masayuki Hosoda, Yasuyuki Hikita, Harold Y. Hwang, Kathryn A. Moler
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  ABSTRACT: In heterostructures of LaAlO3 (LAO) and SrTiO3 (STO), two nonmagnetic insulators, various forms of magnetism have been observed [1-7], which may [8, 9] or may not [10] arise from interface charge carriers that migrate from the LAO to the interface in an electronic reconstruction [11]. We image the magnetic landscape [5] in a series of n-type samples of varying LAO thickness. We find ferromagnetic patches that appear only above a critical thickness, similar to that for conductivity [12]. Consequently we conclude that an interface reconstruction is necessary for the formation of magnetism. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample, indicating that the carriers at the interface do not need to be itinerant to generate magnetism. The fact that the ferromagnetism appears in isolated patches whose density varies greatly between samples strongly suggests that disorder or local strain induce magnetism in a population of the interface carriers.
  Nature Communications 01/2012; 3(922). · 7.40 Impact Factor
• Article: Critical thickness for ferromagnetism in LaAlO₃/SrTiO₃ heterostructures.

  Beena Kalisky, Julie A Bert, Brannon B Klopfer, Christopher Bell, Hiroki K Sato, Masayuki Hosoda, Yasuyuki Hikita, Harold Y Hwang, Kathryn A Moler
  [show abstract] [hide abstract]
  ABSTRACT: In LaAlO(3)/SrTiO(3) heterointerfaces, charge carriers migrate from the LaAlO(3) to the interface in an electronic reconstruction. Magnetism has been observed in LaAlO(3)/SrTiO(3), but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. Using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlO(3) thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.
  Nature Communications 01/2012; 3:922. · 7.40 Impact Factor