Phase coexistence and dynamical behavior inNdNiO3ultrathin films

Abstract

Rare-earth nickelates exhibit several temperature-driven phase transitions that are tunable by the size of the rare-earth ions, pressure, epitaxial strain in ultrathin films etc. We investigate the metal-insulator and Néel transitions in a series of NdNiO3 thin films with varying degrees of lattice mismatch using ultra low frequency electrical noise measurements. The noise magnitude follows a 1/f behavior and is Gaussian in the high temperature paramagnetic metallic phase of the films, however deviations are seen in the low temperature paramagnetic and antiferromagnetic insulating phases. The noise magnitude increases by orders of magnitude at temperatures below the metal-insulator transition and is indicative of inhomogeneous electrical conduction arising from phase separation. The inhomogeneous nature of conduction is corroborated by the presence of a large non-Gaussian noise signature in the low temperature phases. Well below the Neel temperature, the noise behavior evolves between Gaussian and non-Gaussian over several hours pointing to dynamically competing ground states with subtle variations within the antiferromagnetic insulating phase.

Kinetic Spinodal Instabilities in the Mott Transition inV2O3: Evidence from Hysteresis Scaling and Dissipative Phase Ordering

“…But many real systems do spontaneously fall out of equilibrium in a window of thermal hysteresis around the abrupt phase transition (APT) [2]. The accompanying nonergodic behaviorarrested kinetics [3, 4], spatial inhomogeneity [5,6] and phase coexistence [7][8][9], and rate dependence [10-12]-is well documented.Within the mean field (MF) picture, this metastable phase is predicted to abruptly terminate at the spinodals, the two values of field or temperature where the barrier against nucleation vanishes [2,7,[13][14][15][16][17][18]. The analogy between the MF spinodals and the critical point in the power law divergence of susceptibility [2,13,[18][19][20] and their being fixed points under renormalization group transformation [17,21] has long been discussed [2,18,22].…”

“…But many real systems do spontaneously fall out of equilibrium in a window of thermal hysteresis around the abrupt phase transition (APT) [2]. The accompanying nonergodic behaviorarrested kinetics [3,4], spatial inhomogeneity [5,6] and phase coexistence [7][8][9], and rate dependence [10][11][12]-is well documented.…”

“…Such strongly hysteretic "zeroth-order" transitions [62] thus form a new class of transitions that may potentially be observed in many other systems including similar oxides undergoing metal-insulator transition [6,9], manganites [10], intermetallic shape-memory alloys and magnetocaloric materials [63]. A better understanding of the phase transformation kinetics in such systems should help chart the uncertain territory of metastable states in the language of critical phenomena.…”

Charge-transfer-induced interfacial ferromagnetism in La0.7Sr0.3MnO3/NdNiO3

“…The T MIT and T N were reported to be equal (∼180 K) for bulk NNO [54] crystals. For thin films, both the T MIT and T N are reduced, with T N T MIT [55]. In our case, T N = 50 K is far below the T MIT = 120 K. Therefore, the exchange bias effect which was only observed below a blocking temperature of 30 K, is related to the paramagnetic-antiferromagnetic transition of the NNO layer.…”

Nucleation and Growth Bottleneck in the Conductivity Recovery Dynamics of Nickelate Ultrathin Films

“…We investigate epitaxial films of NNO and ENO using optical pump–THz probe (OPTP) spectroscopy and provide a comparison between first- and second-order IMT conductivity dynamics. In the NNO films T IMT ≃ 140 K (compared to 200 K in bulk due to strain in the films), ,, while for the ENO films T N = 200 K (as in bulk) and T IMT ≃ 380 K (100 K lower than in bulk). , Previous time-resolved studies of the IMT in RNiO 3 films focused on vibrational excitation of substrate phonons − or used an optical probe. , Magnetic ,− and charge order dynamics in NNO films were also investigated, as well as in RNiO 4 compounds, , using time-resolved resonant soft X-ray diffraction. As an overview, our conductivity dynamics are initiated with above band gap photoexcitation which induces a thermal quench from the insulating to the metallic state.…”