In the present work, a systematic investigation of electrical transport mechanism has been used as a tool to investigate the charge-order suppression and its crossover in Pr_0.5Ca_0.5MnO₃(PCMO) manganite system with varying particle size and applied magnetic field. The samples with different particle sizes were synthesized by adopting sol-gel method and sintering at different temperatures. The prepared samples were thoroughly characterized by various physicochemical techniques. The activation energy and density of states at Fermi level obtained from the temperature-dependent electrical resistivity data clearly show the charge order crossover signatures and its suppression in the samples below 70 nm particle size and applied magnetic fields above 4 T. The significant change in various electrical transport parameters with the particle size around 70 nm could be attributed to the melting of long-range charge ordering behavior due to surface spin disorder and induced lattice-strain effects in PCMO manganite system.

The investigation of charge ordering (CO) suppression and consequence effects in manganites are of interest to the scientific community as they help them to understand the interactions among the spin, charge and orbital degrees of freedom of conduction electrons. In this work, the suppression of CO in small bandwidth half-doped manganite, Nd_0.5Ca_0.5MnO₃ (NCMO) has been demonstrated by reducing the particle size. Bulk and nano forms of NCMO materials were prepared by sol-gel technique and characterized by various physicochemical techniques. The magnetic and magnetotransport properties of bulk samples show the exciting features, viz., CO, training and irreversible metamagnetic effects, whereas these features are significantly suppressed in the nanoscale sample. The observed behavior in the present investigation was explained in terms of magnetic phase separation and spin memory effects. Our investigation establishes a combined effect of surface spin disorder and lattice strains for the suppression of CO behavior in NCMO manganite system.

The room-temperature magnetoelastic coupling has been demonstrated in (x)NiFe₂O₄+(1-x)BaTiO₃ (where x = 0-1 with a difference of 0.1) composite system by investigating its structural, magnetic and ferroelectric properties. The samples were prepared by a standard solid-state reaction method and characterized by x-ray diffraction, backscattered scanning electron microscopy and energy dispersive x-ray spectroscopy techniques. The temperature dependent magnetization data clearly show the significant jumps in magnetization curves at structural phase transitions of BaTiO₃, signifying the strain-mediated converse magnetoelectric (CME) coupling in NiFe₂O₄-BaTiO₃ multiferroic system. The substantial changes observed in the values of obtained parameters from structural, magnetic and ferroelectric properties clearly ensuring the strain-mediated magnetoelectric (ME) as well as CME effects in this system. The present investigation indicates that the NiFe₂O₄-BaTiO₃ composite system will be a potential candidate for the future low-power consumption device applications at room temperature.

Electric field controlled magnetism is an exciting area of condensed matter physics to explore the device applications at ultra-low power consumption compared to the conventional current controlled or magnetic field controlled devices. In this study, an attempt was made to demonstrate electric field controlled magnetoresistance (MR) in a tri-layer structure consisting of La_0.67Sr_0.33MnO₃ (LSMO) (40 nm)/SrTiO₃ (10 nm)/LSMO (10 nm) grown on a 500-μm-thick BaTiO3 (001) (BTO) single crystal substrate by pulsed laser deposition technique. Epitaxial growth of the trilayer structure was confirmed by x-ray diffraction measurements. Jumps observed in the temperature-dependent magnetization curve at around the structural phase transitions of BTO ensure the strain-mediated magnetoelectric coupling between LSMO and BTO layers. A significant change in MR of this structure in applied electric fields does not show any polarity dependence. The findings are related to the lattice strain-mediated magnetoelectric coupling in ferromagnetic LSMO/ferroelectric BTO heterostructures.

Magnetization reversal has been demonstrated in an Fe layer grown on BaTiO₃(110) single crystal substrate by utilizing the interface magnetic anisotropy induced by lattice strain and a small magnetic field bias. The polar plots of normalized remanent magnetization show isotropic nature at room temperature (293 K), while those at 230 and 175 K exhibit twofold symmetry with the easy axis oriented along [-111]pc of BaTiO3. Cooling and heating cycles in the range of 150–325 K in an applied magnetic field of -35 Oe along [-111]pc enable to achieve the deterministic 180 degree magnetization reversal, where distinct magnetic anisotropies of Fe associated with different structural phases of BaTiO₃ will be the driving force that induces the magnetization reversal. Electric field dependence of the magnetic coercivity shows hysteric behavior, which we attribute to the combined interfacial effect of magnetization rotation in Fe and ferroelectric polarization switching in BaTiO₃.

In this paper we demonstrate significant magnetoelectric coupling in ferrimagnetic, NiFe₂O₄, and ferroelectric, BaTiO₃, multiferroic composite bulk materials by measuring temperature dependent magnetization. X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy data show that the two phases coexist with a highly crystalline and sharp interface without any detectable impurities, which enables significant magnetoelectric (ME) coupling. The temperature dependent magnetization data of the composite clearly show the jumps in magnetization curves at the structural phase transitions of BaTiO₃, thereby indicating their origin in ME coupling. The change in coercivity of composite sample in different ferroelectric phases of BaTiO₃ has been observed compared to the NiFe₂O₄ sample. The different lattice strains corresponding to different ferroelectric phases of BaTiO₃ could be the driving force for modulating the magnetization and coercivity of the composite material. This is clear evidence of strain mediated ME coupling in ferrimagnetic and ferroelectric composite materials.

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