Mott-insulator-to-metal transitions under an applied electric field are currently the subject of ... more Mott-insulator-to-metal transitions under an applied electric field are currently the subject of numerous fundamental and applied studies. Exploring the electronic parameters contributing to the external control of conductivity of correlated systems like V 2 O 3 is an indispensable requirement for next-generation Mottronic devices. Here, we demonstrate a resistive-switching (RS) phenomenon, i.e., a flip from the high-resistance state (HRS) to the low-resistance state in a V 2 O 3 thin film grown on Si (001) substrate by applying a dc voltage as external perturbation. The RS effect is explained in connection with the electronic structure by overcoming the electronic correlations and, in the HRS, the V 2 O 3 /Si film is realized to lie in the intermediate regime between the Mott-Hubbard and charge-transfer insulating states. Interestingly, our study reveals an electrically induced nonthermal RS effect in the V 2 O 3 /Si film in terms of different energetics like on-site Coulomb repulsion (U) and charge-transfer energy (), which regulate the exotic properties of this metal oxide and its functionality.
Gapped spin orders induce electric polarization in multiferroics with strong magnetoelectric (ME)... more Gapped spin orders induce electric polarization in multiferroics with strong magnetoelectric (ME) coupling. The sensitivity of terahertz (THz) radiation to the spin gaps and the dielectric medium can uniquely access this technologically relevant ME effect. Here, we implement magneto-THz time-domain spectroscopy to demonstrate the manifestation of spin-wave excitations responsible for the ME coupling in multiferroic compound Co 4 Nb 2 O 9. We observed two sharp and a weak spin-gap resonance mode at 0.77, 1.58, and 0.91 THz at 5 K below the antiferromagnetic ordering in the absence of magnetic field. In an applied magnetic field, the strength of the 0.77 THz mode decreases while two field-induced modes, namely, the Goldstone mode and magnon excitation, appear at 0.27 and 1.50 THz, respectively. This THz optical evidence of a rich manifestation of field-controlled magnetic resonances, a mutual transfer of optical spectral weight between the zero-field and field-induced excitations, and associated change of complex refractive index in magnetic fields unravel a unique ME coupling in Co 4 Nb 2 O 9 .
The effect of Sr doping in BaTiO 3 (BTO) with nominal compositions Ba 0.80 Sr 0.20 TiO 3 (BSTO) h... more The effect of Sr doping in BaTiO 3 (BTO) with nominal compositions Ba 0.80 Sr 0.20 TiO 3 (BSTO) have been explored in its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (P) of BSTO is much higher than in BTO. The value of P is 5C/cm 2 at room temperature and the maximum P 8C/cm 2 is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature T 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron X-ray diffraction and Raman results shows correlations between P, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed which is related to the appearance of superlattice peak around room temperature due to TiO 6 octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials.
The effect of Cr doping with nominal compositions Mn 2-x Cr x O 3 (0 x 0.10) has been underta... more The effect of Cr doping with nominal compositions Mn 2-x Cr x O 3 (0 x 0.10) has been undertaken to investigate its effect on structural, magnetic, dielectric and magnetoelectric properties. The Cr doping transformed the room temperature crystal structure from orthorhombic to cubic symmetry. Similar to -Mn 2 O 3 , two magnetic transitions have been observed in the Cr doped samples. The effect of Cr doping is significant on the low temperature transition i.e. the lower magnetic transition shifted towards higher temperature (25 K for pristine to 40 K for x=0.10) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in complex dielectric measurements for all compositions around high temperature magnetic ordering. Interestingly, the magnetodielectric behaviour enhanced enormously 21% with Cr substitution as compared to pristine Mn 2 O 3 .
Simultaneous coexistence of room-temperature ferromagnetism and ferroelectricity in Fe doped BaTi... more Simultaneous coexistence of room-temperature ferromagnetism and ferroelectricity in Fe doped BaTiO3 (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-temperature ferroelectric, results in the stabilization of its hexagonal polymorph which is ferroelectric only below ∼ 80K. Here, we investigate its origin and show that Fe doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-temperature ferroelectricity) in Fe doped BTO, we investigate the role of different parameters which primarily control the paraelectric hexagonal phase stability over the ferroelectric tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen-vacancies, to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidt's tolerance factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compound with enhanced room-temperature multiferroic properties.
The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction ... more The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction method. The room temperature (RT) powder X-ray and neutron diffraction has been performed to understand its crystal structure. The X-ray and neutron diffraction data refined using Rietveld analysis which shows the single-phase of the prepared sample with orthorhombic structure (Pcab). The detailed ac electrical measurements were carried out using dielectric constant and impedance spectroscopy at different temperatures at wide frequency range (4 Hz-1 MHz). The temperature dependent dielectric results show sharp increase in dielectric constant near 240 K which can be seen as the frequency dependent peak in tanδ. The non-Debye type dielectric relaxation is observed at broad temperature near room temperature. The contributions of grain and grain boundaries are also explored using impedance spectroscopy.The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction method. The room temperature (RT) powder X-ray and neutron diffraction has been performed to understand its crystal structure. The X-ray and neutron diffraction data refined using Rietveld analysis which shows the single-phase of the prepared sample with orthorhombic structure (Pcab). The detailed ac electrical measurements were carried out using dielectric constant and impedance spectroscopy at different temperatures at wide frequency range (4 Hz-1 MHz). The temperature dependent dielectric results show sharp increase in dielectric constant near 240 K which can be seen as the frequency dependent peak in tanδ. The non-Debye type dielectric relaxation is observed at broad temperature near room temperature. The contributions of grain and grain boundaries are also explored using impedance spectroscopy.
We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 d... more We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 due to ferroelectric to paraelectric phase transition revealed by temperature dependent synchrotron based x-ray absorption and valence band spectroscopy. Valence band spectra show a strong temperature dependence of Ti-3d and O-2p hybridized states around the phase transition. It is observed that Ti-O hybridization is stronger in the paraelectric phase, which is also supported by multiplet calculations at the Ti L-edge. We also find a reduced crystal field value in the paraelectric phase than in the ferroelectric phase, which is caused by volume expansion and a reduction in tetragonal distortion.We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 due to ferroelectric to paraelectric phase transition revealed by temperature dependent synchrotron based x-ray absorption and valence band spectroscopy. Valence band spectra show a strong temperature dependence of Ti-3d and O-2p hybridized states around the phase transition. It is observed that Ti-O hybridization is stronger in the paraelectric phase, which is also supported by multiplet calculations at the Ti L-edge. We also find a reduced crystal field value in the paraelectric phase than in the ferroelectric phase, which is caused by volume expansion and a reduction in tetragonal distortion.
Multiferroics where at least two primary ferroic orders are present and coupled in a single syste... more Multiferroics where at least two primary ferroic orders are present and coupled in a single system constitute an important class of materials. They attracted special consideration as they present both intriguing fundamental physics problems and technological importance for potential multifunctional devices. Here, we present the evidence of multiferroicity and magnetoelectric (ME) coupling in -Mn2O3; a unique binary perovskite. Corresponding to the antiferromagnetic (AFM) ordering around 80K, a clear frequency independent transition is observed in the dielectric permittivity. We showed that electric polarization emerges near AFM regime that can be modulated with magnetic field. The detailed structural analysis using synchrotron radiation X-ray diffraction demonstrates the increase in structural distortion with decreasing temperature, as well as changes in the unit cell parameters and bond lengths across the ferroelectric and magnetic ordering temperatures. This observation of multiferroicity and magnetoelastic coupling in -Mn2O3 provides insights for the exploration of ME coupling in related materials.
The compound Co 4 Nb 2 O 9 (CNO) exhibits interesting magnetoelectric coupling across its antifer... more The compound Co 4 Nb 2 O 9 (CNO) exhibits interesting magnetoelectric coupling across its antiferromagnetic transition temperature (T N). Here, we report the structural, magnetic and complex dielectric properties of polycrystalline CNO within a wide temperature range (120-360 K), well above its T N. The temperature dependent dc magnetization reveals that T N ~27.2 K. The isothermal magnetization results infer the magnetic field induced transition around 11 kOe at 5 K. The temperature dependent real part of complex dielectric behavior shows sharp increase around 160 K with frequency dispersion and a clear frequency dependent peak is observed in tanδ across the same temperature region. This feature corroborates the dielectric relaxation in CNO well above the long range magnetic ordering. Interestingly; the Curie-Weiss behavior of magnetization results deviate from linearity around the same temperature regime (~160 K) which suggests the presence of short range magnetic correlation well above T N. The details impedance spectroscopy results are also analyzed to comprehend the grain and grain boundary contributions.
Optical control and switching of domain configuration are intriguing to overcome the sluggish tim... more Optical control and switching of domain configuration are intriguing to overcome the sluggish time response, hysteresis, and Joule heating losses present in conventional methods where resistive contacts are involved. The effective optical control of the domain configuration has remained challenging and far from fully understood. It has been reported that light polarization can be used to control the domain configuration in BaTiO 3 , however, without much focus on origin of its mechanism. By combining the experimental techniques that are sensitive to the local and average crystal structure and to electric polarization and electronic structure, we detect and demonstrate the optically guided variations in the domain configurations of BaTiO 3 and show that the strain field generated through the bulk photovoltaic effect plays a key role in domain reconfiguration. Complete mechanism of reversible domain control via light polarization is discussed.
Mott-insulator-to-metal transitions under an applied electric field are currently the subject of ... more Mott-insulator-to-metal transitions under an applied electric field are currently the subject of numerous fundamental and applied studies. Exploring the electronic parameters contributing to the external control of conductivity of correlated systems like V 2 O 3 is an indispensable requirement for next-generation Mottronic devices. Here, we demonstrate a resistive-switching (RS) phenomenon, i.e., a flip from the high-resistance state (HRS) to the low-resistance state in a V 2 O 3 thin film grown on Si (001) substrate by applying a dc voltage as external perturbation. The RS effect is explained in connection with the electronic structure by overcoming the electronic correlations and, in the HRS, the V 2 O 3 /Si film is realized to lie in the intermediate regime between the Mott-Hubbard and charge-transfer insulating states. Interestingly, our study reveals an electrically induced nonthermal RS effect in the V 2 O 3 /Si film in terms of different energetics like on-site Coulomb repulsion (U) and charge-transfer energy (), which regulate the exotic properties of this metal oxide and its functionality.
Gapped spin orders induce electric polarization in multiferroics with strong magnetoelectric (ME)... more Gapped spin orders induce electric polarization in multiferroics with strong magnetoelectric (ME) coupling. The sensitivity of terahertz (THz) radiation to the spin gaps and the dielectric medium can uniquely access this technologically relevant ME effect. Here, we implement magneto-THz time-domain spectroscopy to demonstrate the manifestation of spin-wave excitations responsible for the ME coupling in multiferroic compound Co 4 Nb 2 O 9. We observed two sharp and a weak spin-gap resonance mode at 0.77, 1.58, and 0.91 THz at 5 K below the antiferromagnetic ordering in the absence of magnetic field. In an applied magnetic field, the strength of the 0.77 THz mode decreases while two field-induced modes, namely, the Goldstone mode and magnon excitation, appear at 0.27 and 1.50 THz, respectively. This THz optical evidence of a rich manifestation of field-controlled magnetic resonances, a mutual transfer of optical spectral weight between the zero-field and field-induced excitations, and associated change of complex refractive index in magnetic fields unravel a unique ME coupling in Co 4 Nb 2 O 9 .
The effect of Sr doping in BaTiO 3 (BTO) with nominal compositions Ba 0.80 Sr 0.20 TiO 3 (BSTO) h... more The effect of Sr doping in BaTiO 3 (BTO) with nominal compositions Ba 0.80 Sr 0.20 TiO 3 (BSTO) have been explored in its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (P) of BSTO is much higher than in BTO. The value of P is 5C/cm 2 at room temperature and the maximum P 8C/cm 2 is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature T 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron X-ray diffraction and Raman results shows correlations between P, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed which is related to the appearance of superlattice peak around room temperature due to TiO 6 octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials.
The effect of Cr doping with nominal compositions Mn 2-x Cr x O 3 (0 x 0.10) has been underta... more The effect of Cr doping with nominal compositions Mn 2-x Cr x O 3 (0 x 0.10) has been undertaken to investigate its effect on structural, magnetic, dielectric and magnetoelectric properties. The Cr doping transformed the room temperature crystal structure from orthorhombic to cubic symmetry. Similar to -Mn 2 O 3 , two magnetic transitions have been observed in the Cr doped samples. The effect of Cr doping is significant on the low temperature transition i.e. the lower magnetic transition shifted towards higher temperature (25 K for pristine to 40 K for x=0.10) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in complex dielectric measurements for all compositions around high temperature magnetic ordering. Interestingly, the magnetodielectric behaviour enhanced enormously 21% with Cr substitution as compared to pristine Mn 2 O 3 .
Simultaneous coexistence of room-temperature ferromagnetism and ferroelectricity in Fe doped BaTi... more Simultaneous coexistence of room-temperature ferromagnetism and ferroelectricity in Fe doped BaTiO3 (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-temperature ferroelectric, results in the stabilization of its hexagonal polymorph which is ferroelectric only below ∼ 80K. Here, we investigate its origin and show that Fe doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-temperature ferroelectricity) in Fe doped BTO, we investigate the role of different parameters which primarily control the paraelectric hexagonal phase stability over the ferroelectric tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen-vacancies, to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidt's tolerance factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compound with enhanced room-temperature multiferroic properties.
The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction ... more The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction method. The room temperature (RT) powder X-ray and neutron diffraction has been performed to understand its crystal structure. The X-ray and neutron diffraction data refined using Rietveld analysis which shows the single-phase of the prepared sample with orthorhombic structure (Pcab). The detailed ac electrical measurements were carried out using dielectric constant and impedance spectroscopy at different temperatures at wide frequency range (4 Hz-1 MHz). The temperature dependent dielectric results show sharp increase in dielectric constant near 240 K which can be seen as the frequency dependent peak in tanδ. The non-Debye type dielectric relaxation is observed at broad temperature near room temperature. The contributions of grain and grain boundaries are also explored using impedance spectroscopy.The polycrystalline sample of α-Mn2O3 has been synthesized through standard solid-state reaction method. The room temperature (RT) powder X-ray and neutron diffraction has been performed to understand its crystal structure. The X-ray and neutron diffraction data refined using Rietveld analysis which shows the single-phase of the prepared sample with orthorhombic structure (Pcab). The detailed ac electrical measurements were carried out using dielectric constant and impedance spectroscopy at different temperatures at wide frequency range (4 Hz-1 MHz). The temperature dependent dielectric results show sharp increase in dielectric constant near 240 K which can be seen as the frequency dependent peak in tanδ. The non-Debye type dielectric relaxation is observed at broad temperature near room temperature. The contributions of grain and grain boundaries are also explored using impedance spectroscopy.
We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 d... more We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 due to ferroelectric to paraelectric phase transition revealed by temperature dependent synchrotron based x-ray absorption and valence band spectroscopy. Valence band spectra show a strong temperature dependence of Ti-3d and O-2p hybridized states around the phase transition. It is observed that Ti-O hybridization is stronger in the paraelectric phase, which is also supported by multiplet calculations at the Ti L-edge. We also find a reduced crystal field value in the paraelectric phase than in the ferroelectric phase, which is caused by volume expansion and a reduction in tetragonal distortion.We report the modifications in the electronic properties of single phase polycrystalline BaTiO3 due to ferroelectric to paraelectric phase transition revealed by temperature dependent synchrotron based x-ray absorption and valence band spectroscopy. Valence band spectra show a strong temperature dependence of Ti-3d and O-2p hybridized states around the phase transition. It is observed that Ti-O hybridization is stronger in the paraelectric phase, which is also supported by multiplet calculations at the Ti L-edge. We also find a reduced crystal field value in the paraelectric phase than in the ferroelectric phase, which is caused by volume expansion and a reduction in tetragonal distortion.
Multiferroics where at least two primary ferroic orders are present and coupled in a single syste... more Multiferroics where at least two primary ferroic orders are present and coupled in a single system constitute an important class of materials. They attracted special consideration as they present both intriguing fundamental physics problems and technological importance for potential multifunctional devices. Here, we present the evidence of multiferroicity and magnetoelectric (ME) coupling in -Mn2O3; a unique binary perovskite. Corresponding to the antiferromagnetic (AFM) ordering around 80K, a clear frequency independent transition is observed in the dielectric permittivity. We showed that electric polarization emerges near AFM regime that can be modulated with magnetic field. The detailed structural analysis using synchrotron radiation X-ray diffraction demonstrates the increase in structural distortion with decreasing temperature, as well as changes in the unit cell parameters and bond lengths across the ferroelectric and magnetic ordering temperatures. This observation of multiferroicity and magnetoelastic coupling in -Mn2O3 provides insights for the exploration of ME coupling in related materials.
The compound Co 4 Nb 2 O 9 (CNO) exhibits interesting magnetoelectric coupling across its antifer... more The compound Co 4 Nb 2 O 9 (CNO) exhibits interesting magnetoelectric coupling across its antiferromagnetic transition temperature (T N). Here, we report the structural, magnetic and complex dielectric properties of polycrystalline CNO within a wide temperature range (120-360 K), well above its T N. The temperature dependent dc magnetization reveals that T N ~27.2 K. The isothermal magnetization results infer the magnetic field induced transition around 11 kOe at 5 K. The temperature dependent real part of complex dielectric behavior shows sharp increase around 160 K with frequency dispersion and a clear frequency dependent peak is observed in tanδ across the same temperature region. This feature corroborates the dielectric relaxation in CNO well above the long range magnetic ordering. Interestingly; the Curie-Weiss behavior of magnetization results deviate from linearity around the same temperature regime (~160 K) which suggests the presence of short range magnetic correlation well above T N. The details impedance spectroscopy results are also analyzed to comprehend the grain and grain boundary contributions.
Optical control and switching of domain configuration are intriguing to overcome the sluggish tim... more Optical control and switching of domain configuration are intriguing to overcome the sluggish time response, hysteresis, and Joule heating losses present in conventional methods where resistive contacts are involved. The effective optical control of the domain configuration has remained challenging and far from fully understood. It has been reported that light polarization can be used to control the domain configuration in BaTiO 3 , however, without much focus on origin of its mechanism. By combining the experimental techniques that are sensitive to the local and average crystal structure and to electric polarization and electronic structure, we detect and demonstrate the optically guided variations in the domain configurations of BaTiO 3 and show that the strain field generated through the bulk photovoltaic effect plays a key role in domain reconfiguration. Complete mechanism of reversible domain control via light polarization is discussed.
Uploads
Papers by satish yadav