[show abstract][hide abstract] ABSTRACT: We have studied the structure, the surface morphology,the magnetic domains and the magnetization of
ferromagnetic BaFeO3-�δ (BFO) thin films deposited on single-crystal MgO(001) substrate. The BFO film is
ferromagnetic-insulating at room temperature and shows a growth of self organized symmetric square-
shaped structures of various length-scales on the surface. The film, after oxygen annealing, shows several
pronounced modifications: (i) in addition to square structures, the pyramid-shaped structures also
manifest on the surface,(ii) the lattice parameter decreases indicating a change in the structure,(iii) the
magnetization isotherms show magnetic anisotropy with a five-fold increase in magnetic coercivity and
two-fold increase in magnetic moment , and (iv) a larger growth of the magnetic domains. These results
demonstrate a strong influence of oxygen annealing on structural and magnetic properties of BFO films.
Our results suggest that the structural and the magnetic properties are strongly correlated in BFO films,
albeit with unaltered insulating state.
Journal of Magnetism and Magnetic Materials 01/2014; 356:98. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have deposited NdNi1−xMnxO3 (0 ≤ x ≤ 0.10) thin films on SrTiO3 (001), NdGaO3 (001), and YAlO3 (100) substrates and studied the effects of Mn-doping and strain on the charge transport. The majority of charge carriers are holes. Both the in-plane strain and the Mn-doping affect the electrical transport of the films. The metallic state completely vanishes at Mn-doping of x = 0.10. All the films, including x = 0, deposited on SrTiO3 are insulating throughout the temperature range. We find that the resistivity data of all the insulating films fit to two different models, i.e., variable range hopping and Arrhenius equation, in two different temperature regions. The mechanism of charge-transport in the insulating films changes from one type to another and the temperature range of fittings depend on the level of Mn-doping. The results and analyses clearly show that there are contrasting effects of Mn-doping in the metallic and the insulating regions: on one hand, the resistivity increases with increasing Mn-doping in the metallic region; and on the other hand, the hopping/activation of charge carriers get promoted in the insulating region.
Journal of Applied Physics 01/2014; 115(9):093701-093701-6. · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure.
[show abstract][hide abstract] ABSTRACT: We present an unified approach of epitaxial strain and chemical substitution to induce ferromagnetic order in otherwise non-magnetic CaRuO3. The tensile and compressive strained CaRu1−xCrxO3 (0 < x ≤ 0.2) (CRCO) films deposited on SrTiO3 (100) and LaAlO3 (100) substrates, respectively, exhibit a magnetic moment larger than their bulk compositions. The compressive strained x = 0.15 film displays unusually large magnetic moment ∼1.4 μB/f.u. which is about one order of magnitude larger than that of its bulk counterpart. We show that this giant magnetic moment manifests in the realization of (i) a giant exchange bias of ∼700 Oe in CaRu0.85Cr0.15O3/Pr0.5Ca0.5MnO3 bilayer and (ii) a large hysteretic magnetoresistance; both potential attributes for the spintronic applications.
[show abstract][hide abstract] ABSTRACT: Vertical magnetization shift (MShift) coexisting with the conventional exchange bias fields was observed in the epitaxial bilayers of the ferromagnetic SrRuO3 and the G-type antiferromagnetic La0.3Sr0.7FeO3 grown on SrTiO3(111) substrate. We demonstrate this MShift can be tuned from 5% to 36% by controlling the SrRuO3(4–50 nm) and La0.3Sr0.7FeO3(15–140 nm) layer thicknesses. The magnitude of MShift exhibits inverse relation with the thickness of the SrRuO3 layers; in contrast, it increases with increasing the La0.3Sr0.7FeO3 layer thickness up to 105 nm. Thus observed MShift was unambiguously corroborated by the thermoremanent data. This study emphasizes the presence of pinned moments not only at the interface but also across it as-well.
[show abstract][hide abstract] ABSTRACT: The non-magnetic and non-Fermi-liquid CaRuO3 is the iso-structural analog of the ferromagnetic (FM) and Fermi-liquid SrRuO3. We show that an FM order in the orthorhombic CaRuO3 can be established by the means of tensile epitaxial strain. The structural and magnetic property correlations in the CaRuO3 films formed on SrTiO3 (100) substrate establish a scaling relation between the FM moment and the tensile strain. The strain dependent crossover from non-magnetic to FM CaRuO3 was observed to be associated with switching of non-Fermi liquid to Fermi-liquid behavior. The intrinsic nature of this strain-induced FM order manifests in the Hall resistivity too; the anomalous Hall component realizes in FM tensile-strained CaRuO3 films on SrTiO3 (100) whereas the non-magnetic compressive-strained films on LaAlO3 (100) exhibit only the ordinary Hall effect. These observations of an elusive FM order are consistent with the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in tensile CaRuO3. We further establish that the tensile strain is more efficient than the chemical route to induce FM order in CaRuO3.
[show abstract][hide abstract] ABSTRACT: We have fabricated multilayer structure of half-metallic ferromagnet La0.7Sr0.3MnO3 and insulator-metal transition system NdNiO3 on SrTiO3 (100) substrate; thin layers of the former are intercalated in the major matrix of the later. The two structures exhibit pseudomorphic structural coupling with each other. We show that a large increase in the conductivity and an enhanced irreversibility across insulator-metal transition of NdNiO3 may be realized by varying the thickness of La0.7Sr0.3MnO3 and the ratio of thickness of the two layers. Corroborated by the magnetization data, it is shown that the combined effect of structure and magnetism by interfacial coupling is a much better technique than the chemical modification to control the electrical transport of NdNiO3.
[show abstract][hide abstract] ABSTRACT: The half-doped Pr0.5Sr0.5MnO3 (PSMO) manganite represents a unique stripe type of charge orbital order that induces transport and magnetic anisotropy. Low-energy charge dynamics in PSMO (110) epitaxial film were investigated along and across two dissimilar in-plane orthogonal axes, [1-10] and , by recording the complex refractive index in the energy range of 1–7 meV. We report a novel observation of a gradual crossover from Drude-like metallic conductivity to charge-density-wave (CDW)–like collective excitations as the polarized terahertz excitation field is swept across the orthogonal in-plane axes. This is a rare manifestation of a CDW mode in a highly conducting stripe-type charge-ordered (CO) system, which is fundamentally different from the CDW modes of checkerboard CO. Interestingly, the contrasting charge dynamics along orthogonal in-plane axes form an intrinsic electronic switch, apparently a consequence of the unique CO of PSMO.
Physical Review B 06/2013; 87(22). · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: Effects of the tensile and compressive epitaxial strain and the crystallographic orientations on the structural and magnetic properties of (Bi0.9La0.1)2FeCrO6 (BLFCO) films were studied. The BLFCO (001) films (30 nm and 70 nm) were deposited on various single crystal substrates having lattice mismatch with the film in the range of −4.16% to +7.2%. We find that a pronounced ferromagnetic order manifests in the coherently strained films compared to that in the partially strained films. The saturation magnetic moment exhibits dissimilar effects on the type of the lattice mismatch: the coherent tensile strain is less favorable than the coherent compressive strain for the magnetic order in these films. We further establish that the ferromagnetic order exhibits maximum magnetic moment for (111)-oriented and minimum for (110)-oriented coherently strained BLFCO epitaxial films.
[show abstract][hide abstract] ABSTRACT: The behavior of charge-density wave (CDW) condensates with the systematic introduction of ferromagnetic (FM) and spin-glass phases in the charge-ordered (CO) lattice of Nd(0.5)Sr(0.5)MnO(3) (NSMO) and Eu(0.5)Sr(0.5)MnO(3) (ESMO) epitaxial thin films was investigated by terahertz time-domain spectroscopy. The optical conductivity of (100)-oriented NSMO film, in which the CO lattice has an insignificant volume of the FM phase, exhibits a peak with attributes of CDW collective excitation at ∼3.2 meV. This peak becomes completely submerged in the Drude continuum as the volume of the epitaxial strain-induced FM phase increases in the CO state of (110)- and (111)-oriented NSMO films. In contrast, the ESMO (100) film, having a short-range CO phase amid a spin-glass-like state, displays a subtle CDW peak in conductivity. Modeling the optical terahertz conductivity with the phenomenological Lorentz-Drude relation and extracting the optical weight due to both contributions (Lorentz and Drude), it was found that the manifestation of CDW condensates is associated with the generic strength of charge ordering and that the condensate suffers a more pronounced suppression when FM order dilutes the CO lattice than when spin-glass disorder weakens the CO state.
[show abstract][hide abstract] ABSTRACT: We have studied the effects of Mn-doping in a series of
NdNi1-xMnxO3 (x = 0, 0.10) thin films deposited on
NdGaO3 (001) and YAlO3 (100) substrates,
respectively with tensile and compressive in-plane strains.
Interestingly, only 10% Mn-doping totally suppresses the metallicity in
both the thin films indicating an opening of charge-transfer gap. In
addition, we have also observed contrasting effects of compressive and
tensile strains on electrical transport of Mn-doped thin films. There is
an enhancement in magnetization as a result of Mn-doping.
[show abstract][hide abstract] ABSTRACT: We show that a ferromagnetic (FM) order in the orthorhombic CaRuO3, which is
a non-magnetic and iso-structural analog of FM system SrRuO3, can be
established and stabilized by the means of tensile epitaxial strain.
Investigations on the structural and magnetic property correlations in the
CaRuO3 films with different degrees of strain reveal that the FM moment
increases with increasing the tensile strain. This is an experimental
verification to the theoretical predictions of scaling of the tensile epitaxial
strain and the magnetic order in this system. Our studies further establish
that the tensile strain is more efficient than the chemical route to induce the
FM order in CaRuO3 as the magnetic moment in these strained films is larger
than that in chemically modified CaRu0.9Cr0.1O3 films.
[show abstract][hide abstract] ABSTRACT: We have deposited NdNi1−xMnxO3 (0 ≤ x ≤ 0.10) thin films on two different substrates, YAlO3 (1 0 0) and NdGaO3 (0 0 1), respectively, to explore the effects of Mn-doping with compressive and tensile strain. These films show metal–insulator transitions, except for two films with x = 0.10. The Hall coefficient measurements show that the majority of charge carriers are holes in these films. Increasing Mn-doping linearly decreases the temperature coefficient of resistance in the conducting temperature-region. The resistivity increases systematically with increasing Mn-doping in the films with tensile strain, whereas it non-monotonically decreases with doping in thin films with compressive strain. This study reveals competition and combination of different effects of the Mn-doping and of the strain, where the competition and the combination depend on the temperature-region and the type of strain. In addition to the effects of electronic configuration of Mn ions on the free carrier concentration, we find that the effects of Mn-doping on the resistivity are also mediated by the structure, and moulded under the influence of strain. The effects of Mn-doping and strain are distinguished and explained here.
Journal of Physics D Applied Physics 01/2013; 46(41):415305. · 2.53 Impact Factor
[show abstract][hide abstract] ABSTRACT: We show that a charge-density wave mode submerged in large conductivity of the stripe-type charge-ordered (CO) crystal of Pr0.5Sr0.5MnO3 (PSMO) can be extracted by exciting selective crystallographic planes using polarized terahertz field. Low energy (1–7 meV) dynamics have been explored in the (100), (110), and (111) epitaxial films of PSMO manganite. Of (110) and (111) films representing bulk-like CO, the former exhibits a peak in the conductivity-energy spectrum with attributes of charge-density wave mode along a specific in-plane axis. On the contrary, the CO (111) and the phase-separated (100) films lack this low energy mode but exhibit a Drude-like spectral behavior in the metallic regime. These studies reveal a variety in isothermal charge dynamics originating from the anisotropic nature of the stripe charge-order.
[show abstract][hide abstract] ABSTRACT: Heavily doped rare-earth manganite Eu0.42Sr0.58MnO3 exhibits long range
charge-ordering with modulation wave vector of q = 1/3. We have used
terahertz (THz) time domain spectroscopy to probe low energy dynamics in
Eu0.42Sr0.58MnO3 (100) epitaxial films in the energy range of 1-6 meV
and in the temperature range of 40-320 K. Observation of a finite
frequency peak structure in optical conductivity at around 3.5 meV
suggests the existence of collective excitations due to charge-density
[show abstract][hide abstract] ABSTRACT: We have explored the low-energy excitations in epitaxial thin films of Eu1-xSrxMnO3 [x = 0.50: spin-glass with short range charge-order and x = 0.58: long range charge-order] using terahertz time-domain spectroscopy. A finite frequency peak structure in optical conductivity is observed at ∼3.5 meV for both the films. While peak structure of x = 0.58 film possesses distinct properties of low-energy collective excitations of charge-density waves, the same is subtle and shallower with weaker peak conductivity for x = 0.50 film. These data, corroborated by magnetization, provide unambiguous evidence of the effect of range of charge-ordering, pinning, and disorder (induced by spin-glass state) on the manifestation of charge-density waves.
[show abstract][hide abstract] ABSTRACT: We have explored the low-energy dynamics in the half-doped Eu0.5Sr0.5MnO3 using terahertz time domain (TDS) spectroscopy. Observation of a finite frequency peak structure in optical conductivity at around ∼4meV suggests low-energy excitation, presumably the charge-density waves.
[show abstract][hide abstract] ABSTRACT: Terahertz time domain spectroscopy was employed to explore the low-energy dynamics in the half-doped Nd0.5Sr0.5MnO3 (100) films. We have observed evolution of a peak structure in conductivity at around ∼4 meV which suggests the existence of charge-density waves.