Magnetodielectric Coupling Research Articles

Temperature-dependent electrical and magneto-dielectric properties of 0.7Bi0.99Nd0.01Fe0.99(Co, Ti)0.01O3-0.3CaTiO3 composite

0.7Bi0.99Nd0.01Fe0.99(Co, Ti)0.01O3-0.3CaTiO3 (BNFCTO-CaTO) composite was prepared by using sol-gel method. The structural formation was investigated using the XRD pattern, which confirms the presence of distorted rhombohedral structure with space group R3c and the superlattice orthorhombic crystal structure with space group Pbmn. The dielectric behavior of BNFCTO-CaTO has been studied within the frequency range of 100 Hz to 1 MHz from 300 K to 773 K. The sample shows dielectric dispersion in low frequency region that can be explained by Maxwell-Wagner type interfacial polarization. The temperature-dependent dielectric plot shows an anomaly near to magnetic transition temperature (TN) of BiFeO3 and shows relaxor behavior. Furthermore, BNFCTO-CaTO shows a strong magneto-dielectric coupling effect at room temperature.

Emergent multiferroism with magnetodielectric coupling in EuTiO3 created by a negative pressure control of strong spin-phonon coupling

Negative pressure has emerged as a powerful tool to tailor the physical properties of functional materials. However, a negative pressure control of spin-phonon coupling for engineering magnetism and multiferroicity has not been explored to date. Here, using uniform three-dimensional strain-induced negative pressure in nanocomposite films of (EuTiO3)0.5:(MgO)0.5, we demonstrate an emergent multiferroicity with magnetodielectric coupling in EuTiO3, matching exactly with density functional theory calculations. Density functional theory calculations are further used to explore the underlying physics of antiferromagnetic-paraelectric to ferromagnetic-ferroelectric phase transitions, the spin-phonon coupling, and its correlation with negative pressures. The observation of magnetodielectric coupling in the EuTiO3 reveals that an enhanced spin-phonon coupling originates from a negative pressure induced by uniform three-dimensional strain. Our work provides a route to creating multiferroicity and magnetoelectric coupling in single-phase oxides using a negative pressure approach.

Spin reorientation and magnetodielectric anomalies in FexO1+x (x = 2,3) thin films-effect of microwave radiations

Materials with remarkable magnetodielectric properties are promising candidates for multifunctional devices. Microwave assisted sol-gel method is adopted to synthesize iron oxide thin films under microwave irradiations of 180 W-1000 W. Ferromagnetic response of sols is observed at 360–450 W, 630 W and 720 W powers, while superparamagnetic behavior is obtained at 810 W-1000 W. Films prepared using sols synthesized at 180 W, 270 W and 540 W exhibit amorphous nature. α-Fe2O3 phase is observed at microwave power (MW) of 360 W-450 W. γ-Fe2O3 phase is observed at MW of 630 W and 720 W and Fe3O4 phase is observed at 810–1000 W. Highest saturation magnetization of 45.23emu/cm3, 248.403emu/cm3 and 419.43emu/cm3are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. The transition of Verwey in Fe3O4 thin film is observed at ∼ 115.2 K, whereas γ-Fe2O3 phase does not show any such variation. Further, α-Fe2O3 phase show spontaneous magnetization at low temperatures from FC/ZFC curves. Highest dielectric constant of ∼ 54.26, 84.19 and 121.34 (log f = 5.0) are observed for α-Fe2O3, γ-Fe2O3 and Fe3O4, respectively. Magnetodielectric coupling (MDE) of ∼ −3.9%, −5.1% and −7.5% is obtained for α-Fe2O3, γ-Fe2O3 and Fe3O4 thin films. Fe3O4 phase is found to exhibit peculiar MDE coupling with respect to other phases, revealing exotic magnteodielectric coupling anomalies.

Spin-lattice-charge coupling in quasi-one-dimensional spin-chain NiTe2O5

A high-quality ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$ single crystal was grown via the flux method and characterized using synchrotron x-ray diffraction (XRD) and electron probe microscopy techniques. The dc magnetization $(M)$ confirms the antiferromagnetic long-range ordering temperature $({T}_{\mathrm{N}})$ at 28.5 K. An apparent domelike dielectric anomaly near ${T}_{\mathrm{N}}$, with scaling of magnetodielectric (MD) coupling with magnetization $(\mathrm{MD}%\ensuremath{\propto}{M}^{2})$, signifies higher-order magnetoelectric (ME) coupling. The critical finding is that magnetoelastic coupling plays a pivotal role in bridging the electrical and magnetic dipoles, which was further confirmed by temperature-dependent XRD. In addition, the theoretical charge density difference maps indicate that the emergence of electrical dipoles between the Ni and O atoms below ${T}_{\mathrm{N}}$ originates through $p\text{\ensuremath{-}}d$ hybridization. Thus, the $p\text{\ensuremath{-}}d$ hybridization-induced magnetoelastic coupling is considered a possible mechanism for the higher-order ME effect in this quasi-one-dimensional spin-chain ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$.

Effect of Ni Substitution on Structural, Dielectric, and Ferroelectric Properties and Variation in Magnetocapacitance of Single-Phase Ba0.7Pb0.3TiO3 Ceramic

The present study demonstrates the influence of Ni substitution on the structural, dielectric, and ferroelectric properties of single-phase Pb-doped BaTiO3, that is, Ba0.7Pb0.3TiO3 (BPT) ceramic, and variations in the magnetocapacitance. The hydroxide co-precipitation method was employed to fabricate single-phase Pb-doped BaTiO3 and Ni-substituted Ba0.7Pb0.3TiO3, as Ba0.7Pb0.3TiO3-(x)Ni for x = 0.05, 0.1, and 0.15. Rietveld refinement reflects the single-phase tetragonal crystal structure of pure Ba0.7Pb0.3TiO3 and at higher Ni concentrations, the detection of rhombohedral crystal symmetry of the NiO phase confirms the biphasic structure of the composite. The ferroelectric-paraelectric transition temperature decreased from 274 °C for pure Ba0.7Pb0.3TiO3 to 162 °C for the composite with a higher Ni concentration of x = 0.15. A drastic change in the typical ferroelectric (P-E) loop of Ba0.7Pb0.3TiO3 was observed with the substitution of Ni. The composite with a higher concentration had the highest value of the magnetodielectric coupling coefficient, MD (%) = −2.86. This study reflects an easy and useful approach to achieve two-order parameter coupling with doping of acceptor ions in the ferroelectric phase. This kind of material substantially plays a vital role in the advanced electromagnetic devices for futuristic applications.

Strain-induced modulation of magnetodielectric and magnetoelectric coupling in pzt/cfo thin films grown by rf-sputtering

The miniaturization of systems devices based on the magnetoelectric effect requires a better understanding of the factors that rule the coupling at the interface between different materials in magnetoelectric composites. In this context, this work presents the influence of stress generated at the interface PZT-CFO on multiferroic properties and the magnetodielectric coupling of the PbZr0,2Ti0,8O3/CoFe2O4 heterostructures fabricated by RF-Sputtering technique. It was found that tensile stress generated in the PZT/CFO interface modifies both XRD patterns and ferromagnetic hysteresis loop, inducing an additional contribution to the magnetic anisotropy compared with CFO and PZT layers. In addition, the dielectric properties of the PZT/CFO system are ruled by interfacial charges that accumulate in the PZT-CFO interface. On the other hand, changes in dielectric permittivity as a function of magnetic field (i.e., the magnetodielectric effects) result of the association between the ferroelectric domain movement modulated by stress on the PZT phase due to magnetostriction generated by the CFO phase and the magnetoelectric polarization contribution properly characterized by changes in the remnant polarization due to a magnetic field.

Large magnetodielectric coupling in the vicinity of metamagnetic transition in 6H–perovskite Ba3GdRu2O9

The 6H-perovskites Ba3RRu2O9 (R = rare earth element) demonstrate the magnetodielectric (MD) coupling as a manifestation of 4d–4f magnetic interactions. Here, a detailed study of the structural, magnetic, heat capacity, and MD properties of the 6H-perovskite Ba3GdRu2O9 is reported. The signature of long-range antiferromagnetic (AFM) ordering ∼14.8 K (T N) is evident from the magnetization and heat capacity studies. The T N shifts towards the lower temperature side, apart from splitting in two with the application of the magnetic field. Field-dependent magnetization at 2 K shows three metamagnetic transitions with the opening of small hysteresis in different regions. A new transition at T 1 emerges after the onset of the first metamagnetic transition. Complex magnetic behavior is observed in different magnetic field regions whereas these field regions themselves vary with the temperature. Dielectric response recorded at zero and 80 kOe field exhibits the development of MD coupling well above T N. The MD coupling (∼4.5% at 10 K) is enhanced by 25% as compared to the Dy counterpart. Effect of complex magnetic behavior is also conveyed in the MD results where the maximum value of MD coupling is observed in the vicinity of 10 K (onset of T 1) and near the second metamagnetic transition. Our investigation suggests that both Gd and Ru moments align simultaneously at T N. Short-range magnetic ordering is possibly responsible for MD coupling above T N.

Microwave scattering behaviour of carbon black/ molybdenum di sulphide /cobalt composite for electromagnetic interference shielding application

Erasing signature of an object from an enemy's radar is, tactically, disruptive move achieved by the effective electromagnetic interference (EMI) shield. We report on the microwave scattering (2–18 GHz) behaviour of the nano-composite for architecting efficient shield composed of carbon black (CB), molybdenum di sulphide (MoS2) and cobalt (Co). Nano-composite, prepared by a facile, solid state synthesis route, are characterized using infrared, x-ray diffractometry, UV–visible, energy dispersive x-ray spectroscopic techniques including scanning electron microscopy. In infrared and Rayleigh analysis, formation of -C-Mo-C, OSO, Mo–O, and Co–O phases generated asymmetric polarization at low % CB content that gets transformed into a symmetric mode due to formation of Co–O and Co–S–C radicals at high CB % to cause maximum power losses. Possible polarization mechanism is discussed. In constitutive analysis, two-fold increase in the dielectric function, the dual behaviour (Debye and Jonscher) of the ac conductivity, and the synergistic magneto-dielectric coupling factor influenced the scattering performance of the composite. Broadly, at 18% composition, the shielding effectiveness is recorded to be > 97@14 GHz with 7.7 GHz of the bandwidth and the thickness ∼2.5 mm. The Dallenbach return loss is almost 75% revealing a high-performance shield design @18% CB/MoS2/Co nano-composite.

Temperature-dependent magnetodielectric, magnetoimpedance, and magnetic field controlled dielectric relaxation response in KBiFe2O5

In this work, polycrystalline KBiFe2O5 (KBFO), belonging to the brownmillerite class of monoclinic structure with space group P2/c, is synthesized using a solid-state reaction route. Magnetodielectric (MD) and magnetoimpedance (MI) characteristics of KBFO are studied over a wide temperature (10–300 K), magnetic field (0–1.3 T), and frequency (100 Hz to 1 MHz) range. Zero-field-cool (ZFC) and field-cool (FC) magnetization data show a bifurcation around 11 K, indicating blocking temperature (TB). At room temperature, MD and MI data as a function of the magnetic field shows maximum MD and MI coupling to be ∼−0.6% and ∼0.7%, respectively, at 50 kHz. With the decrease in temperature from 300 K to 50 K, magnetodielectric strength decreases (−0.6% to −0.06%), whereas magnetization increases from canted-antiferromagnetic (MS ≈ 0.16 emu g−1) to a weak ferromagnetic state (MS ≈ 0.44 emu g−1). It indicates the existence of Inverse Dzyaloshinskii-Moriya interaction causing MD coupling in KBFO. MD behavior is also reflected in magnetic field-dependent dielectric relaxation phenomena demonstrated through magnetic field-dependent activation energies. The difference in activation energies of magnetic field-dependent conduction mechanism (Eg ≈ 0.370 ± 0.018 eV) and MD loss relaxation (Eg ≈ 0.183 ± 0.006 eV) indicate both have a different origin. The presence of the capacitive MI effect demonstrates that the observed magnetodielectric coupling is intrinsic. The existence of both temperatures-dependent MD and MI coupling in KBFO makes it suitable for dynamic random access memory as well as novel magnetic sensors.

Magnetodielectric coupling in barium titanate–cobalt ferrite composites obtained via thermally-assisted high-energy ball milling

In this work, a magnetodielectric coupling observed in barium titanate–cobalt ferrite composites synthesized using high-energy ball milling assisted via a thermal treatment is discussed. Vibrating sample magnetometry and dielectric spectroscopy showed that multiferroic composites possess both ferromagnetic and dielectric behaviors inherited from the parent ferromagnetic cobalt ferrite and ferroelectric barium titanate phases. The magnetocapacitance (up to 35%) recorded for x = 0.3, (1-x)BaTiO3–xCoFe2O4, can be attributed to the spin-dependent filtering mechanism. The composite with the aforementioned composition exhibited a homogeneous matrix–particle composite microstructure, which was achieved via high-energy ball milling during the mixing stage.

Intertwined magnetization and exchange bias reversals across compensation temperature in YbCrO3 compound

We have investigated the origin of magnetization and exchange bias (EB) reversals in the $\mathrm{YbCr}{\mathrm{O}}_{3}$ compound at the magnetization compensation temperature, ${T}_{\mathrm{COMP}}$ of 16.5 K by dc magnetization, ac susceptibility, neutron diffraction (ND), neutron depolarization, specific heat, and dielectric measurements. A weak magnetization $({M}_{\mathrm{Cr}})$ is observed below the N\'eel temperature ${T}_{\mathrm{N}}$ (\ensuremath{\sim}120 K) in dc magnetization, which is consistent with a canted antiferromagnetic (AFM) state due to ordering of ${\mathrm{Cr}}^{3+}$ moments. Specific heat data exhibit a \ensuremath{\lambda}-shaped peak at ${T}_{\mathrm{N}}$. Further, a monotonic increase of ac susceptibility at low temperatures and the Schottky anomaly in the specific heat data account for the polarized nature of the ${\mathrm{Yb}}^{3+}$ moment $({M}_{\mathrm{Yb}})$ under the molecular field of the AFM ${\mathrm{Cr}}^{3+}$ sublattice. Our ND study has confirmed a finite polarized ${\mathrm{Yb}}^{3+}$ ordered moment, and the ${G}_{\mathrm{z}}$-type AFM ordering of ${\mathrm{Cr}}^{3+}$ moments below ${T}_{\mathrm{N}}$. The temperature variations of the lattice constants $a$ and $b$ show a crossover from positive to negative thermal expansion (NTE) across the ${T}_{\mathrm{COMP}}$ while cooling. Below ${T}_{\mathrm{COMP}}$, the separation between Cr-Cr atoms lying in the $ab$ plane increases with decrease in temperature, which corroborates with the observed NTE of the lattice constants. In the present compound, the sign change of the net magnetization arising out of the AFM coupled polarized ${\mathrm{Yb}}^{3+}$ $({M}_{\mathrm{Yb}})$ and the ferromagnetic ${\mathrm{Cr}}^{3+}$ $({M}_{\mathrm{Cr}})$ sublattice moments results in the sign reversal of magnetization. Interestingly, anomalous behavior of the coercive field with its minimum value at $T\ensuremath{\sim}{T}_{\mathrm{COMP}}$ is observed. EB also changes sign at $T\ensuremath{\sim}{T}_{\mathrm{COMP}}$. Moreover, the temperature variation of the real part of the dielectric constant reveals an anomaly at ${T}_{\mathrm{COMP}}$, indicating a weak magnetodielectric coupling in the $\mathrm{YbCr}{\mathrm{O}}_{3}$ compound. A training effect analysis ensures the conventional nature of the observed EB. Neutron depolarization study sheds light on the temperature-dependent domain magnetization with its zero value at the ${T}_{\mathrm{COMP}}$. The presence of the observed important phenomena viz. magnetization and EB reversals in a single-phase compound suggests their possible use in making magnetization switching, spin-value, thermomagnetic, and other spintronic devices.

Multiferroic, optical and magneto-dielectric properties with enhanced magneto-impedance characteristic of KBiFe2O5

KBiFe2O5 (KBFO) is an interesting multiferroic compound with the coexistence of ferroelectric and ferromagnetic phases with a narrow band gap. In this work, KBiFe2O5 (KBFO) is synthesized using a sol-gel technique, followed by calcination at 973 K. Rietveld refinement analysis of XRD data confirms the presence of monoclinic crystal structure with space group P2/c. The SEM micrograph of KBFO reflects the irregular shape of grains with slight agglomeration. The optical band gap measured by UV visible spectroscopy of KBFO is found to be 1.56 eV. The multiferroic behavior of KBFO has been confirmed by the electrical (dielectric) and magnetic (M-H loop) measurements. A weak ferromagnetic nature is observed due to canting of the magnetic moment of G-type anti-ferromagnetic ordering. The dielectric studies reveal the Maxwell-Wagner type dispersion and an anomaly near magnetic phase transition temperature. KBFO shows negative magneto-dielectric (MD) coupling as both ε and tan δ decreases with the increasing magnetic field. Impedance spectroscopy is performed to analyze the intrinsic and extrinsic effects in MD coupling. The Nyquist plot shows positive magneto-resistance and negative magneto-capacitance which represent strong MD coupling in KBFO. It also reveals that the bulk property (intrinsic effect) dominates over the extrinsic effect in the sample. These results affirm that KBFO is a new candidate for room-temperature multiferroicity with a suitable bandgap and strong MD coupling for photovoltaic applications.

Understanding the correlation between orbital degree of freedom, lattice-striction and magneto-dielectric coupling in ferrimagnetic Mn1.5Cr1.5O4

Dielectric anomaly observed in cubic Mn1.5Cr1.5O4 around ferrimagnetic ordering temperature (T N) suggests a possible magneto-dielectric coupling in the system. This report confirms the presence of a weak but significant magneto-dielectric coupling in the system. The ab initio calculations show a band gap of around 1.2 eV, with Fermi-level closer to the conduction band. The major features of conduction band nearest to the Fermi-level correspond to d xz and d 3z 2 −r 2 orbitals of Mn3+ ion. Temperature-dependent neutron diffraction results show a rapid decay in structural parameters (lattice-striction and transition metal–oxygen bond length) around T N. We confirmed that these changes in structural parameters at T N are not related to structural transition but the consequences of orbital-ordering of Mn3+. The rapid decay in transition metal–oxygen bond length under internal magnetism of the system shows that magnetism could certainly manipulate the electric dipole moment and hence the dielectric constant of the system. Magneto-striction acts as a link between magnetic and dielectric properties.

Magnetic phase diagram, magnetoelastic coupling, and Grüneisen scaling in CoTiO3

High-quality single crystals of ${\mathrm{CoTiO}}_{3}$ are grown and used to elucidate in detail structural and magnetostructural effects by means of high-resolution capacitance dilatometry studies in fields up to 15 T which are complemented by specific heat and magnetization measurements. In addition, we refine the single-crystal structure of the ilmenite ($R\overline{3}$) phase. At the antiferromagnetic ordering temperature ${T}_{\mathrm{N}}$ pronounced $\ensuremath{\lambda}$-shaped anomaly in the thermal expansion coefficients signals shrinking of both the $c$ and $b$ axes, indicating strong magnetoelastic coupling with uniaxial pressure along $c$ yielding six times larger effect on ${T}_{\mathrm{N}}$ than pressure applied in-plane. The hydrostatic pressure dependency derived by means of Gr\"uneisen analysis amounts to $\ensuremath{\partial}{T}_{\mathrm{N}}/\ensuremath{\partial}p\ensuremath{\approx}2.7(4)\phantom{\rule{4pt}{0ex}}\mathrm{K}/\mathrm{GPa}$. The high-field magnetization studies in static and pulsed magnetic fields up to 60 T along with high-field thermal expansion measurements facilitate in constructing the complete anisotropic magnetic phase diagram of ${\mathrm{CoTiO}}_{3}$. While the results confirm the presence of significant magnetodielectric coupling, our data show that magnetism drives the observed structural, dielectric, and magnetic changes both in the short-range ordered regime well above ${T}_{\mathrm{N}}$ as well as in the long-range magnetically ordered phase.

Enhanced magnetic and magnetodielectric properties of Co-doped brownmillerite KBiFe2O5 at room temperature

We report significant enhancement in magnetic and magnetodielectric (MD) properties of cobalt (Co) doped polycrystalline KBiFe2O5 (KBFO). Rietveld refinement of X-ray diffraction data confirms monoclinic crystal structure with P2/c space group. SEM micrographs confirmed the polycrystalline nature of the samples with grain sizes varying from 1 µm to 5 µm. Raman spectra demonstrate the shifting of vibrational modes due to Co doping which is associated with FeO4 tetrahedral. The shift in vibrational modes due to Co doping is in line with the observed changes in FeO4 tetrahedral bond angles (O1-Fe-O1 & O1-Fe-O2) and bond lengths (Fe-O1 & Fe-O2) obtained from XRD data. Room temperature magnetization data reveal the maximum enhancement in Mr (~103 times) and Ms (~200 times) values for 5% Co-doped KBFO compared with KBFO. This enhancement in magnetization data is due to a spin-canted (Fe3+) antiferromagnetic spin structure and increased lattice strain with increased cobalt substitution. The temperature-dependent dielectric and magnetization data show an anomaly near 770 K (Tc) indicates the MD effect. Compared to KBFO, nearly ten times enhancement in MD and nearly 50 times reduction in magnetic loss (ML) is observed for KBFCO5 measured at 30 kHz frequency. Landau free energy approach confirms the biquadratic nature of MD coupling, and the strength is − 8 (emu/g)2 for 5% Co-doped KBFO and − 5(emu/g)2 for 10% Co-doped KBFO, respectively. The comparative study reveals that Co substitution in KBFO enhances maximum MD% and magnetization in 5% Co substitution. These results establish the coupling between electric and magnetic orders, which can find application in AC/DC magnetic field sensors and ME solar cells.

Magnetodielectric coupling and multi-blocking effect in the Ising-chain magnet Sr2Ca2CoMn2O9

We have demonstrated magnetodielectric (MD) coupling in an Ising-chain magnet Sr2Ca2CoMn2O9 via detailed investigation of ac susceptibility and dielectric constant as a function of temperature, magnetic field, and frequency. Sr2Ca2CoMn2O9 consists of spin-chains made of the regular stacking of one CoO6 trigonal prism with two MnO6 octahedra. The (Co2+–Mn4+–Mn4+) unit stabilizes a (↑↓↑) spin-state along the chains that are distributed on a triangular lattice. This compound undergoes a partially disordered antiferromagnetic transition at TN ∼ 28 K. The dielectric constant exhibits a clear peak at TN only in the presence of an external magnetic field (H ≥ 5 kOe), evidencing the presence of MD coupling, which is further confirmed by field-dependent dielectric measurements. We argue that spatial inversion symmetry can be broken as a result of exchange-striction along each spin chain, inducing uncompensated local dipoles. At low temperatures, a dipolar relaxation phenomenon is observed, bearing strong similarities to the blocking effect typical of spin dynamics in this compound. Such a spin-dipole relationship is referred to as a “multiblocking” effect, in relation to the concept of magnetodielectric “multiglass” previously introduced for related materials.

Low field magnetotransport behavior of barium hexaferrite/ferromagnetic manganite bilayer

Adding functionalities to existing ferroelectric/ferromagnetic materials showed promising results with exciting physical mechanisms. Pure and bilayer films of strong ferromagnetic oxides, viz, BaFe12O19 (BaM) and La0.67Sr0.33MnO3 (LSMO), were fabricated by pulsed laser deposition. Polycrystalline samples of dense structure, uniform thickness, and monodispersed grain distributions were used to form capacitor-like stack geometry for dielectric and magneto-dielectric (MD) measurements. High dielectric constants at moderately high frequencies with increased relaxation times were observed for the bilayer film and are attributed to the BaM/LSMO strained interface, while Maxwell–Wagner polarization plays an insignificant role. Modeling of dielectric loss tangents and AC conductivity revealed localized carrier hopping between Fe ions in the bilayer film. Pronounced hysteresis loops with a small coercive field and increased saturation magnetization values of BaM/LSMO bilayers, as compared with BaM/Pt, are demonstrated at 300 K; where the role of mixed valence Mn ions in +3 and +4 states at the bottom LSMO electrode is highlighted. MD measurements with varying magnetic fields showed magnetically tunable, large MD coupling values (∼287%) for BaM/LSMO/Pt. The phenomenally high MD values are discussed based on ionic polarization, colossal magnetoresistance of LSMO, and magnetostriction at the BaM/LSMO interface. Our findings propose significant applications of ferromagnetic oxide bilayers in the emerging field of magneto-dielectric coupling devices.

Spin polarization and magneto-dielectric coupling in Al-modified thin iron oxide films -microwave mediated sol-gel approach

Production of single-phase materials with multifunctional properties is still a challenge faced by material scientists. In addition, obtaining high spin polarization efficiency in the materials that exhibit multifunctional properties is a big issue. A novel approach is suggested in this work for obtaining multifunctionality and spin polarization in the same material. This approach has combined the effect of microwave radiations and aluminum (Al) doping in iron oxide thin films during synthesis. Combined effect of microwave radiations and Al doping results in controlling / tuning the structural transitions in iron oxide thin films. Pristine and 2–10 wt% Al doped iron oxide thin films are prepared and studied in detail. Raman analysis shows that 2 and 4 wt% Al concentration results in γ-Fe2O3 + Fe3O4 phase with 71.3% and 64.5% of γ-Fe2O3 content, respectively. XRD and Raman analyses confirm the transition from γ-Fe2O3 to Fe3O4 thin films at Al concentrations of 6–10 wt%. Structural transformation shows that microwave radiations catalyzes that Al3+ions to occupy the vacancies on B sites of iron oxide thus, lead to the formation of Fe3O4. Observation of Verwey transition ~ 126 K also supports the transition in phases of iron oxide with increase in saturation magnetization from 251.3emu/cm3 (pristine films) to 405.6emu/cm3 (8 wt% Al concentration). High dielectric constant of ~ 135.5 (log f = 5.0) is observed for 8 wt% Al concentration. Conductivity and detailed impedance & modulus analyses depict Mott’s hopping phenomenon along with presence of different relaxation times. Coupling between magnetic and dielectric properties is observed at room temperature. Magnetoresistance curves indicate spin polarization efficiency of ~24%.

Magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6

Iridium-based double perovskites having mixed 3d–5d–4f magnetic sub-lattices are expected to exhibit exotic magnetic phenomenon. In this paper, we report a study of structural, magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6 (SMCO), which crystallizes in monoclinic structure with space group P21/n and the crystal symmetry remains same throughout the measured temperature down to 15 K. High resolution synchrotron x-ray diffraction reveals an isostructural phase transition around 104 K. Magnetization measurements on polycrystalline samples indicate that SMCO orders ferrimagnetically at T FiM = 104 K; while, a second transition is observed below 10 K due to the rare-earth (Sm3+) ordering. The ferrimagnetic transition is well-understood by Néel's two-sublattice model, which is primarily ascribed to antiferromagnetic coupling between Co2+ and Ir4+ sub-lattices. Electronic transport measurement shows the insulting behaviour of SMCO, which follows Mott variable-range hopping conduction mechanism. However, dielectric measurements as a function of temperature rules out the presence of magneto dielectric coupling in this compound.

Ferroelectric and magnetic domain mapping of magneto-dielectric Ce doped BiFeO3 thin films

Co-existent ferroelectric and magnetic ordering at room temperature in multiferroics has generated significant interest for potential applications in low-power sensors, transducers, and memory devices. Despite tremendous efforts centered on site-substitution in BiFeO3 to attain enhanced functionality, local probing of multiferroic domain dynamics with dopant concentration remains overlooked. Here we report a detailed investigation on ferroelectric and magnetic domain mapping of Bi1−XCeXFeO3; 0 ≤ X ≤ 0.2 (BCFOX) thin films and discussed concentration-dependent behavior of piezo-response switching, piezo-actuation butterfly-loop and phase-hysteresis, and magneto-dielectric coupling. Large piezo-response amplitude change of 30 mV and near to complete phase reversal of ~150° together with homogeneous magnetic domain distribution and an enhanced magneto-dielectric coupling coefficient of 2.15% at 0.3 T unveils improved ferroelectric ordering in polycrystalline BCFO0.12 thin film. We believe, our findings will develop a comprehensive understanding of sensitive force microscopy technique for the custom-made advancement of BiFeO3 based multiferroic family.