arXiv subjects
Publications and source records attributed to Satya Prakash Pati.
The observation of room temperature ferromagnetism along with a low temperature paramagnetic counterpart in undoped Cu-Cu2O-rGO nanocomposite was demonstrated. A phenomenological approach was taken to explain the observations based on 3D Ising model for arbitrary spins generated due to Cu vacancy in the Cu2O system preferably at the interface.
The electric manipulation of antiferromagnets has become an area of great interest recently for zero-stray-field spintronic devices, and for their rich spin dynamics. Generally, the application of antiferromagnetic media for information memories and storage requires a heterostructure with a ferromagnetic layer for readout through the exchange-bias field. In magnetoelectric and multiferroic antiferromagnets, the exchange coupling exerts an additional impediment (energy barrier) to magnetization reversal by the applied magnetoelectric energy. We proposed and verified a method to overcome this barrier. We controlled the energy required for switching the magnetic domains in magnetoelectric \cro films by compensating the exchange-coupling energy from the ferromagnetic layer with the Zeeman energy of a small volumetric spontaneous magnetization found for the sputtered \cro films. Based on a simplified phenomenological model of the field-cooling process, the magnetic and electric fields required for switching could be tuned. As an example, the switching of antiferromagnetic domains around a zero-threshold electric field was demonstrated at a magnetic field of 2.6 kOe.
The scaling of antiferromagnetic ordering temperature of corundum-type chromia films have been investigated. Néel temperature $T_N$ was determined from the effect of perpendicular exchange-bias on the magnetization of a weakly-coupled adjacent ferromagnet. For a thick-film case, the validity of detection is confirmed by a susceptibility measurement. Detection of $T_N$ was possible down to 1-nm-thin chromia films. The scaling of ordering temperature with thickness was studied using different buffering materials, and compared with Monte-Carlo simulations. The spin-correlation length and the corresponding critical exponent were estimated, and they were consistent between experimental and simulation results. The spin-correlation length is an order of magnitude less than cubic antiferromagnets. We propose that the difference is from the change of number of exchange-coupling links in the two crystal systems.
Chromium(III) oxide is a classical collinear antiferromagnet with a linear magnetoelectric effect. We are presenting the measurements of the magnetoelectric susceptibility $α$ of a sputter-deposited 500-nm film and a bulk single-crystal of Cr$_\mathrm{2}$O$_\mathrm{3}$. We investigated the magnetic phase-transition and the critical exponent $β$ of the sublattice magnetization near Néel temperature. For the films, an exponent of 0.49(1) was found below 293 K, and changed to 1.06(4) near the Néel temperature of 298 K. For the single-crystal, the exponent was constant at 0.324(4). We investigated the reversal probability of antiferromagnetic domains during magnetoelectric field cooling. For the sputtered films, reversal probability was zero above 298 K and stabilized only below 293 K. We attribute this behavior to formation of grains during film growth, which gives different intergrain and intragrain exchange-coupling energies. For the single-crystal, reversal probability was stabilized immediately at the Néel temperature of 307.6 K.
In this study, we investigated the effect of spacer and buffer layers on the blocking temperature TB of the perpendicular exchange bias of thin Cr2O3 films, and revealed a high TB of 260 K for 20-nm-thick Cr2O3 thin films. By inserting a Ru spacer layer between the Cr2O3 and Co films and changing the spacer thickness, we controlled the magnitude of the exchange bias and TB. By comparing the TB values of the 20-nm-thick Cr2O3 films on Pt and alpha-Fe2O3 buffers, we investigated the lattice strain effect on the TB. We show that higher TB value can be obtained using an alpha-Fe2O3 buffer, which is likely because of the lattice-strain-induced increase of Cr2O3 magnetic anisotropy.