•Low temperature neutron diffraction data reveal non-collinear magnetic structure in Co4Ta2O9.•Neutron diffraction data fit best to a non-centro-symmetric crystal structure below Neel ...temperature.•Correlation between magnetic structure and improper ferroelectricity is analyzed for Co4Ta2O9.•Co-existing large magnetoelectric coupling is determined in the spin-flop phase of Co4Ta2O9.
We study magnetocapacitance (MC) effect and magnetoelectric (ME) coupling in spin-flop driven antiferromagnet Co4Ta2O9. Powder neutron diffraction data reveal that the magnetic structure corresponds to a non-collinear arrangement along with a non-centrosymmetric crystal structure below Néel Temperature. Electric polarization is achieved below Néel temperature only when the sample is cooled in the presence of external magnetic field. The magnetocapacitance data at high magnetic fields are analyzed by phenomenological Ginzburg-landau theory of ferro-electromagnets and it is found that change in dielectric constant is proportional to the square of magnetization. The saturation polarization and magnetoelectric coupling are estimated to be 52 µC/m2 and γ = 1.4 × 10−3 (emu/g)−2 respectively at 6 Tesla. Strong magnetoelectric coupling and ferroelectric phase in the anti-ferromagnetic Co4Ta2O9 are correlated to magnetic structure as derived from neutron diffraction data.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Room temperature magnetodielectric (MD) effect of Co substituted KBiFe2O5 is reported.•Magnetic data confirms the maximum enhancement in Mr (~103 times) and Ms (~200 times) values for ...KBiFe1.9Co0.1CO5 sample.•KBiFe1.9Co0.1CO5 sample shows nearly ten times increment in the MD effect.•The origin behind the observed MD effect is adddressd in detail.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
•KBiFe2O5 (KBFO) is prepared via a solid-state reaction route and crystallizes in the monoclinic phase (P2/c).•The observed magnetodielectric (MD) coupling suggests that Inverse Dzyaloshinskii-Moriya ...interaction could be the origin.•The maximum MD and magnetoimpedance (MI) couplings measured at room temperature are −0.6% and 0.7%, respectively.•The capacitive MI effect suggests that the observed MD in KBFO is intrinsic.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The magnetic state of low temperature martensite phase in Co-substituted Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) has been investigated, in view of numerous conflicting reports of ...occurrences of spin glass (SG), superparamagnetism (SPM) or long range anti-ferromagnetic (AF) ordering. Combination of DC magnetization, AC susceptibility and small angle neutron scattering (SANS) studies provide clear evidence for AF order in the martensitic phase of Ni
Co
Mn
Sn
alloy and rule out SPM and SG orders. Identical studies on another alloy of close composition, Ni
Co
Mn
Sn
, point to the presence of SG order in the martensitic phase and the absence of SPM behavior, contrary to earlier reports. SANS results do show the presence of nanometre-sized clusters but they are found to grow in size from 3 nm at 30 K to 11 nm at 300 K, and do not correlate with magnetism in these alloys.
•Detailed magnetic property study from low temperature to room temperature.•Temperature dependent neutron diffraction study.•Magnetic structure determination.•Relationship of magnetic property study ...and magnetic structure.•Theoretical study.
Magnetic chalcogenide compounds have a great potential in the field of spintronics and biomedical applications. Unlike magnetic transition metal oxides, the study on magnetic chalcogenides is sparse. Here we investigate the magnetic, thermodynamic and electronic properties of a ternary chalcogenide, Mn2SnS4. Contrary to most of the 214-chalcogenide compounds which crystallize in well-known olivine structure with space group Pnma, the title compound, Mn2SnS4, crystallizes in the orthorhombic space group, Cmmm. Magnetic measurements reveal two distinct magnetic transitions: (i) an antiferromagnetic ordering below 152 K, (ii) a weak ferromagnetic ordering, possibly due to spin canting and frustration below 53 K. Neutron diffraction study at 100 K suggest that the magnetic moments (spins) within {1 1 1} planes are ordered ferromagnetically and the adjacent {1 1 1} planes are coupled antiferromagnetically, however, the magnetic spins are not collinear rather canted. LMTO-ASA calculation on an antiferromagnetic model indicates that the compound is poorly metallic in nature and the manganese spins are completely spin polarized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The polycrystalline spinel ZnMn2O4 was prepared using general solid-state reaction method. The room temperature X-ray diffraction pattern was analyzed by Rietveld refinement using FULLPROF software, ...which provides tetragonal symmetry with space group I41/amd. The bonds between transition metals and oxide ions in Infrared spectroscopy confirm ZnMn2O4 phase. Further, the Ńeel temperature is found to be ~297 K from our temperature dependent DC magnetic susceptibility graph, which is different from reported results. The M − H curve at 2 K confirms the formation of anti-ferromagnetic order. We further plan to carry out the temperature dependent neutron diffraction studies which will assist us in further understanding the true magnetism in this spinel oxide.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Strong dependence of Ferromagnetic phase fraction on divalent doping.•Similar crystalline structure but different magnetic and transport properties.•Composition dependent octahedral distortions.
We ...present a comparative study of the effect of divalent doping on structural, magnetic and magneto-transport properties of (La0.4Pr0.6)1-xCaxMnO3 (x = 3/8, 1/3) mixed phase manganites. Structural analysis, using X-ray and neutron diffraction studies, reveals a similar orthorhombic crystal structure with Pnma space group for both the samples; however, x = 3/8 composition shows higher octahedral distortion. The temperature dependent resistivity shows signature of a first order metal-insulator transition with conduction through percolative paths for both the samples. A broad thermal hysteresis observed in temperature dependent magnetization as well as magneto-transport data indicates coexistence of different magnetic phases like metallic ferromagnet, and insulating charge ordered antiferromagnetic in both the manganites. The variation of magnetization profiles with temperature for these stoichiometrically similar compositions is found to be remarkably different, with the dominance of charge ordered-antiferromagnetic phase in the x = 3/8 composition and ferromagnetism in the x = 1/3 composition. The field dependent magnetization isotherms show significantly higher fraction (≈2 times) of ferromagnetic phase in x = 1/3 composition as compared to x = 3/8 composition. The metal-insulator transition temperature is also found to be higher for composition with x = 1/3 (155 K) than that for x = 3/8 (112 K). In an applied magnetic field of 8 T, the resistivity changes drastically as the charge order melts and gives way to stable ferromagnetic metallic behaviour with higher metal-to-insulator transition temperature. The temperature dependent magnetoresistance shows a significant variation for the samples, with maximum value of around 3 × 105% and 7 × 104% for x = 3/8 and x = 1/3 compositions, respectively. These observations suggest that inspite of a very small variation in divalent doping, the magnetic phase fractions in these two manganites are significantly different.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Structural and magnetic phase-transitions in La1-xSrxMnO3+δ (x = 0.67 & 0.71) have been studied employing x-ray diffraction, neutron diffraction and transmission electron microscopy (TEM) in ...conjunction with electrical-transport and magnetic studies. These studies reveal a cubic to incommensurate (IC) charge-ordered (CO) tetragonal phase-transition in both the samples with k-vector varying with temperature and thus indicates charge density wave-like nature. Followed by magnetic transition from paramagnetic phase to incommensurate antiferromagnetic phase. The nearly equal expansion of the a,b axes in the ab plane and the contraction of the c-axis (i.e. type-I Jahn-Teller distortion (JTD)) indicate that the CO is accompanied by a planer ferro-ordering of 3dx2−y2 orbitals in the ab plan, which is different from haring-bone type orderingof3d3x2−r2/3d3y2−r2 orbitals, commonly observed in narrow bandwidth CO manganites. For x = 0.71, a second phase-transition from type-I JTD-CO phase (c < a) to charge disorder type-II JTD tetragonal phase (c > a) was observed. Through EDAX analysis in TEM, a nano-scale marginal composition difference has been observed to lead to nanoscale phase-coexistence. These studies have revealed first microscopic evidence of CO and nano-scale multiphase coexistence in La1-xSrxMnO3-δ with x = 0.67 & 0.71.
•Complex magneto-structural phase diagram.•New charge orbital ordering state and charge density wave nature.•Nano scale phase coexistence.•Incommensurate antiferromagnetic spin ordering.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
•Nd2CoTiO6 is prepared and first time nonmagnetic ion (Ti4+) at B″ site is chosen.•Canted antiferromagnetic spin of Co2+, Nd3+ are confirmed from neutron diffraction.•Magnetization measurement ...results are clarified from neutron diffraction analysis.•Experimental observations are well explained from first principle DFT analysis.
The magnetic, dielectric and structural properties of a double perovskite oxide Nd2CoTiO6 (NCTO), synthesized by solid state reaction method, have been studied. The Rietveld refinement of the room temperature neutron diffraction (ND) pattern specifies that the crystal structure of NCTO is monoclinic with space group P21/n, which contains an ordered array of alternate CoO6 and TiO6 octahedra. Magnetization measurements, carried out from room temperature to 2 K indicate a transition at ∼17 K. The rise of magnetization sharply below ∼17 K is attributed to the magnetic ordering of Nd3+ ions. Ac susceptibility data recorded in the range 70 K–5 K ruled out the presence of spin glass behavior in NCTO. To confirm the nature of magnetic ordering, temperature-dependent ND measurements were carried out and the analysis of ND data recorded at 15 K and 3 K shows the presence of canted antiferromagnetic spin structure of NCTO at low temperatures. Thermal variation of dielectric permittivity shows an anomaly at ∼720 K. First principles density functional theory (DFT) has been invoked to determine the band structure of the sample. The electronic structure has also been extensively investigated to correlate different observed properties of the sample.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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