arXiv subjects

Ankur Rastogi

Publications and source records attributed to Ankur Rastogi.

4 recordsLinked to original sources

arXiv2019

Vectorial observation of the spin Seebeck effect in epitaxial NiFe$_2$O$_4$ thin films with various magnetic anisotropy contributions

We have developed a vectorial type of measurement for the spin Seebeck effect (SSE) in epitaxial NiFe$_2$O$_4$ thin films which have been grown by pulsed laser deposition on MgGa$_2$O$_4$ (MGO) with (001) and (011) orientation as well as CoGa$_2$O$_4$ (011) (CGO), thus varying the lattice mismatch and crystal orientation. We confirm that a large lattice mismatch leads to strain anisotropy in addition to the magnetocrystalline anisotropy in the thin films using vibrating sample magnetometry and ferromagnetic resonance measurements. Moreover, we show that the existence of a magnetic strain anisotropy in NiFe$_2$O$_4$ thin films significantly impacts the shape and magnitude of the magnetic-field-dependent SSE voltage loops. We further demonstrate that bidirectional field-dependent SSE voltage curves can be utilized to reveal the complete magnetization reversal process, which establishes a vectorial magnetometry technique based on a spin caloric effect.

cond-mat.mes-hall↗

arXiv2018

Room-temperature ferromagnetic insulating state in highly cation-ordered epitaxial oxide double perovskite

Ferromagnetic insulators (FMIs) are one of the most important components in developing dissipationless electronic and spintronic devices. However, since ferromagnetism generally accompanies metallicity, FMIs are innately rare to find in nature. Here, novel room-temperature FMI films are epitaxially synthesized by deliberate control of the ratio of two B-site cations in the double perovskite Sr2FeReO6. In contrast to the known ferromagnetic metallic phase in stoichiometric Sr2FeReO6, a FMI state with a high Curie temperature (Tc~400 K) and a large saturation magnetization (MS~1.8 μB/f.u.) is found in highly cation-ordered Fe-rich phases. The stabilization of the FMI state is attributed to the formation of extra Fe3+-Fe3+ and Fe3+-Re6+ bonding states, which originate from the excess Fe. The emerging FMI state by controlling cations in the epitaxial oxide perovskites opens the door to developing novel oxide quantum materials & heterostructures.

cond-mat.mtrl-sci↗

arXiv2018

Single Crystal High Entropy Perovskite Oxide Epitaxial Films

The first examples of single crystal epitaxial thin films of a high entropy perovskite oxide are synthesized. Pulsed laser deposition is used to grow the configurationally disordered ABO3 perovskite, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, epitaxially on SrTiO3 and MgO substrates. X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates. Atomically-resolved electron energy loss spectroscopy mapping shows a uniform and random distribution of all B-site cations. The ability to stabilize perovskites with this level of configurational disorder offers new possibilities for designing materials from a much broader combinatorial cation pallet while providing a fresh avenue for fundamental studies in strongly correlated quantum materials where local disorder can play a critical role in determining macroscopic properties.

cond-mat.mtrl-sci↗

arXiv2010

Two-dimensional superconductivity at a Mott-Insulator/Band-Insulator interface: LaTiO3/SrTiO3

Transition metal oxides display a great variety of quantum electronic behaviours where correlations often play an important role. The achievement of high quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO3 and a band insulator SrTiO3. The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. Here we show that despite the expected electronic correlations, LaTiO3/SrTiO3 heterostructures undergo a superconducting transition at a critical temperature Tc=300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm. We discuss the electronic properties of this system and review the possible scenarios.

cond-mat.supr-con↗