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CPM SeminarSuperparamagnetism at oxide interfaces revealed by scanning SQUID-on-tip microscopyYonathan AnahoryThe Hebrew University of JerusalemNanoSQUIDs residing on the apex of a quartz tip (SOT), suitable for scanning probe microscopy with record size, spin sensitivity, and operating magnetic fields, are presented [1]. We have developed SOT made of Pb with an effective diameter of 46 nm and flux noise of Φn = 50 nΦ0/Hz1/2 at 4.2 K that is operational up to unprecedented high fields of 1 T [1]. The corresponding spin sensitivity of the device is Sn = 0.38 μB/Hz1/2, which is about two orders of magnitude more sensitive than any other SQUID to date. This new device paves the way to magnetic imaging of numerous nanoscaled systems exhibiting exciting physics. This technique is used to study nanoscale magnetism present in systems such as atomically sharp oxide heterostructures. These systems exhibit a range of novel physical phenomena that do not occur in the parent bulk compounds. The most prominent example is the appearance of highly conducting and superconducting states at the interface between the band insulators LaAlO3 and SrTiO3. Here we report a new emergent phenomenon at the LaMnO3/SrTiO3 interface in which an antiferromagnetic insulator abruptly transforms into a magnetic state that exhibits unexpected nanoscale superparamagnetic dynamics. Upon increasing the thickness of LaMnO3 above five unit cells, our scanning nanoSQUID-on-tip microscopy shows spontaneous formation of isolated magnetic islands of 10 to 50 nm diameter, which display random moment reversals by thermal activation or in response to an in-plane magnetic field[2]. Our charge reconstruction model of the polar LaMnO3/SrTiO3 heterostructure describes the sharp emergence of thermodynamic phase separation leading to nucleation of metallic ferromagnetic islands in an insulating antiferromagnetic matrix. The model further suggests that the nearby superparamagnetic-ferromagnetic transition can be gate tuned, holding potential for applications in magnetic storage and spintronics.
[1] D. Vasyukov, Y. Anahory, L. Embon,
D. Halbertal, J. Cuppens, L. Neeman, A. Finkler,
Y. Segev, Y. Myasoedov, M. L. Rappaport,
M. E. Huber, and E. Zeldov, Nature Nanotech. 8, 639
(2013)
Thursday, March 24th 2016, 15:30
Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) |