- Cinthia Piamonteze: Using heterostructures to create new magnetic states
- 3. 11. 2021, 14:10
- online (zoom)
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Abstract:
Complex oxides with perovskite structures exhibit a variety of interesting properties, such as metal-insulator transitions, superconductivity, colossal magnetoresistance, among others. These properties appear due to the interconnection between atomic, electronic and magnetic structure. The possibility to combine these systems in heterostructures, where different materials are deposited in sequence, adds some more degrees of freedom that allow controlling or creating new properties. In heterostructures, symmetry breaking and proximity effects can lead to new properties originating from the interface.
In this talk, I will present two examples of how magnetic properties can be modified or enhanced in heterostructures. The main technique used for unveiling the magnetism in these ultra-thin films, is x-ray magnetic circular dichroism (XMCD). An introduction to XMCD will also be given.
The first system presented will be heterostructures composed of manganites and ruthenates. Manganites with 1/3 doping, such as La2/3B1/3MnO3 (where B is a 2+ ion such as Sr, Ca or Ba) exhibit colossal magnetoresistance, ferromagnetic ordering temperature (TC) above room temperature and semimetal conduction, which are interesting features for application on devices. However, it was soon found that below a certain thickness these films are no longer ferromagnetic, which was attributed to a "dead" magnetic layer. In the heterostructure we investigated it was verified that an ultra-thin manganite layer (1-2 layers) is ferromagnetic when in contact with SrRuO3. The reason for this stability of ferromagnetic properties can be attributed to the electronic structure of the multilayer as well as the magnetic coupling between Mn and Ru. This shows how heterostructure engineering can be used to enhance the ferromagnetic state lost in the ultra-thin single films. [1]
In the second example, we investigate multilayers of nickelates and manganites. Nickelates RNiO3 (R = rare earth) have a transition from metal to insulator with decreasing temperature. At low temperature these systems order in an unconventional antiferromagnetic structure. For NdNiO3 and PrNiO3 the electronic and magnetic transitions occur at the same temperature. In our work, we investigated thin layers of nickelates in contact with optimally doped manganites (La0.7Sr0.3MnO3) which are ferromagnetic metals below TC. Our results on angular resolved photoemission spectroscopy shows the absence of the metal-insulator transition in NdNiO3 when in contact with LSMO. XMCD investigation shows that NdNiO3 has a ferromagnetic interface which appears to be correlated with the observed change in electronic properties. This exemplifies how proximity effects can be used to create new electronic and magnetic states in ultra-thin films. [2]
[1] Piamonteze, C. et al. Ferromagnetic order of ultra-thin La0.7Ba0.3MnO3 sandwiched between SrRuO3 layers. Applied Physics Letters 118, 152408 (2021). doi:10.1063/5.0043057
[2] Caputo, M. et al. Proximity-Induced Novel Ferromagnetism Accompanied with Resolute Metallicity in NdNiO3 Heterostructure. Advanced Science 2101516 (2021). doi:10.1002/advs.202101516