Nonpolar resistive memory switching with all four possible resistive switching modes in amorphous ternary rare earth LaHoO3 thin films

We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO3 (LHO) thin films for non-volatile resistive random access memory (RRAM) applications. Nonpolar resistive switching (RS) was achieved in PtLHOPt memory cells with all four possible RS modes ( positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high RON and ROFF ratios (in the range of 104 to 105) and non-overlapping switching voltages (set voltage, VON 3.6 to 4.2 V and reset voltage, VOFF 1.3 to 1.6 V) with a small variation of about 5 to 8 percent. X ray photoelectron spectroscopic studies together with temperature dependent switching characteristics revealed the formation of metallic holmium (Ho) and oxygen vacancies (VO) constituted conductive nanofilaments (CNFs) in the low resistance state (LRS). Detailed analysis of current versus voltage characteristics further corroborated the formation of CNFs based on metal like (Ohmic) conduction in LRS. Simmons Schottky emission was found to be the dominant charge transport mechanism in the high resistance state.

Phonons correlation with magnetic excitations in weak ferromagnet YCrO3

We report on the temperature dependent Raman spectroscopic studies of orthorombic distorted perovskite YCrO3 in the temperature range of 20-300K. Temperature dependence of DC-magnetization measurement under field cooled and zero field cooled modes confirmed the transition temperature (TN ~142K) and anomalous characteristic temperature (T* ~60K), above which magnetization tends to saturate. Magnetization isotherm recorded below TN at 125K shows clear loop opening without magnetization saturation up to 20kOe, indicating the coexistence of antiferromagnetic (AFM) interaction with weak ferromagnetic (WFM) phase. Mean field calculation for exchange constants further confirms the complex magnetic phase below TN. Temperature evolution of lineshape parameters of selected modes (associated with the octahedral rotation and A-shift in the unit cell) revealed anomalous phonon shift near Cr3+ magnetic ordering temperature (TN ~142K). Additional phonon anomaly was identified at T* ~60K in agreement with the magnetization results and reflects the change in spin dynamics, plausibly due to the change in Cr-spin configuration. Moreover, the positive and negative shift in Raman frequency below TN revel the existence of competing WFM and AFM exchanges. The phonon shift of B3g (3)-octahedral rotation mode fairly scaled with the square of sublattice magnetization from TN to T*, below which it start to depart from theconventional behaviour and need further attention. This correlation between magnetic and Raman data elucidate the spin-phonon coupling owing to the multiferroic phenomenon in YCrO3.