soumen mandal | Beijing Institute of Technology (original) (raw)
Papers by soumen mandal
Journal of Physics-condensed Matter, 2005
Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic fi... more Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn(1-x)Co(x)O [Formula: see text] epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for [Formula: see text], all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x>0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (>10(20) cm(-3)). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T>2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s-d exchange dominated transport in these dilute magnetic semiconductors.
Physical Review B, 2008
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y 1−x Pr x Ba 2 Cu 3 O 7 sandwiched between two ferromagnetic La 2/3 Sr 1/3 MnO 3 layers is examined. At low external field (H ext ), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H c ) of the magnetic layers. At H ext ≫ H c , a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ (Pr-YBCO, 0⩽x⩽0.4 ) are reported over a broad range of temperature and magnetic-field strength. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature (Tc) . This effect is attributed to vortexlike excitations in the phase incoherent condensate existing above Tc . A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc≈110K for disorder-free YBa2Cu3O7-δ .
Applied Physics Letters, 2006
The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM prox... more The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM proximity ef-fect junctions provides valuable information on the degree of spin polarization in the ferromagnet, exchange-field-induced inhomogeneous superconductivity at the ...
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-\delta}$(Pr-YBCO, 0$\leq x\leq$0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(T$_c$). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above T$_c$. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a T$_c\approx$110K for disorder-free YBa$_2$Cu$_3$O$_{7-\delta}$.
![Research paper thumbnail of A comparative study of angle dependent magnetoresistance in [001] and [110] $La_{2/3}Sr_{1/3}MnO_3](https://attachments.academia-assets.com/32534907/thumbnails/1.jpg)
](The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ ... more The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Magnetism and Magnetic Materials, 2008
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−δ (Pr-YBCO, 0≤ x ≤0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(Tc). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above Tc. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc ≈110K for disorder-free YBa2Cu3O 7−δ .
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$ sandwiched between two ferromagnetic La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ layers is examined. At low external field ($H_{ext}$), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H$_c$) of the magnetic layers. At H$_{ext} \gg$ H$_c$, a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
![Research paper thumbnail of A Comparative Study of Angle Dependent Magnetoresistance in [001] and [110] La 2/3 Sr 1/3 MnO 3](https://attachments.academia-assets.com/49308219/thumbnails/1.jpg)
](Journal of Superconductivity and Novel Magnetism, 2011
The angle dependent magnetoresistance study on [001] and [110] La2/3Sr1/3MnO3 thin films shows th... more The angle dependent magnetoresistance study on [001] and [110] La2/3Sr1/3MnO3 thin films shows that the anisotropy energy of [110] films is higher than that of a [001] oriented La2/3Sr1/3MnO3 film of similar thickness. The data have been analyzed in the light of a multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Physics-condensed Matter, 2005
Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic fi... more Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn(1-x)Co(x)O [Formula: see text] epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for [Formula: see text], all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x>0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (>10(20) cm(-3)). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T>2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s-d exchange dominated transport in these dilute magnetic semiconductors.
Physical Review B, 2008
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y 1−x Pr x Ba 2 Cu 3 O 7 sandwiched between two ferromagnetic La 2/3 Sr 1/3 MnO 3 layers is examined. At low external field (H ext ), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H c ) of the magnetic layers. At H ext ≫ H c , a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ (Pr-YBCO, 0⩽x⩽0.4 ) are reported over a broad range of temperature and magnetic-field strength. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature (Tc) . This effect is attributed to vortexlike excitations in the phase incoherent condensate existing above Tc . A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc≈110K for disorder-free YBa2Cu3O7-δ .
Applied Physics Letters, 2006
The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM prox... more The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM proximity ef-fect junctions provides valuable information on the degree of spin polarization in the ferromagnet, exchange-field-induced inhomogeneous superconductivity at the ...
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-\delta}$(Pr-YBCO, 0$\leq x\leq$0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(T$_c$). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above T$_c$. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a T$_c\approx$110K for disorder-free YBa$_2$Cu$_3$O$_{7-\delta}$.
![Research paper thumbnail of A comparative study of angle dependent magnetoresistance in [001] and [110] $La_{2/3}Sr_{1/3}MnO_3](https://attachments.academia-assets.com/32534903/thumbnails/1.jpg)
](The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ ... more The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Magnetism and Magnetic Materials, 2008
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−δ (Pr-YBCO, 0≤ x ≤0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(Tc). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above Tc. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc ≈110K for disorder-free YBa2Cu3O 7−δ .
Journal of Physics-condensed Matter, 2005
Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic fi... more Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn(1-x)Co(x)O [Formula: see text] epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for [Formula: see text], all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x>0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (>10(20) cm(-3)). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T>2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s-d exchange dominated transport in these dilute magnetic semiconductors.
Physical Review B, 2008
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y 1−x Pr x Ba 2 Cu 3 O 7 sandwiched between two ferromagnetic La 2/3 Sr 1/3 MnO 3 layers is examined. At low external field (H ext ), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H c ) of the magnetic layers. At H ext ≫ H c , a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ (Pr-YBCO, 0⩽x⩽0.4 ) are reported over a broad range of temperature and magnetic-field strength. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature (Tc) . This effect is attributed to vortexlike excitations in the phase incoherent condensate existing above Tc . A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc≈110K for disorder-free YBa2Cu3O7-δ .
Applied Physics Letters, 2006
The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM prox... more The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM proximity ef-fect junctions provides valuable information on the degree of spin polarization in the ferromagnet, exchange-field-induced inhomogeneous superconductivity at the ...
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-\delta}$(Pr-YBCO, 0$\leq x\leq$0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(T$_c$). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above T$_c$. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a T$_c\approx$110K for disorder-free YBa$_2$Cu$_3$O$_{7-\delta}$.
The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ ... more The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Magnetism and Magnetic Materials, 2008
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−δ (Pr-YBCO, 0≤ x ≤0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(Tc). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above Tc. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc ≈110K for disorder-free YBa2Cu3O 7−δ .
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$ sandwiched between two ferromagnetic La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ layers is examined. At low external field ($H_{ext}$), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H$_c$) of the magnetic layers. At H$_{ext} \gg$ H$_c$, a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
Journal of Superconductivity and Novel Magnetism, 2011
The angle dependent magnetoresistance study on [001] and [110] La2/3Sr1/3MnO3 thin films shows th... more The angle dependent magnetoresistance study on [001] and [110] La2/3Sr1/3MnO3 thin films shows that the anisotropy energy of [110] films is higher than that of a [001] oriented La2/3Sr1/3MnO3 film of similar thickness. The data have been analyzed in the light of a multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Physics-condensed Matter, 2005
Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic fi... more Magnetotransport measurements are performed over a broad range of temperature (T) and magnetic field (H) on highly degenerate n-type Zn(1-x)Co(x)O [Formula: see text] epitaxial films. The cobalt-free samples are characterized by a metallic resistivity ρ(T) down to 2 K, a negative and predominantly isotropic magnetoresistance (MR) and optical transmission above 85% in the visible range of the electromagnetic spectrum. X-ray diffraction measurements show that while for [Formula: see text], all cobalt atoms occupy the tetrahedral sites of the wurtzite structure of ZnO, a phase separation into CoO is seen for x>0.2. In the solution phase, we do not observe any signatures of a spontaneous ordering of the cobalt spins despite a large concentration of mobile electrons (>10(20) cm(-3)). The absence of anomalous Hall resistance is consistent with this observation. The carrier concentration (n) over the entire range of x remains above the Mott limit for the insulator-to-metal transition in a doped semiconductor. However, while the Co-free samples are metallic (T>2 K), we see a resistivity (ρ) minimum followed by lnT divergence of ρ(T) at low temperatures with increasing x. The magnetoresistance of these samples is negative and predominantly isotropic. Moreover, the MR tends to follow a logH behaviour at high fields. These observations, including the Kondo-like minimum in the resistivity, suggest s-d exchange dominated transport in these dilute magnetic semiconductors.
Physical Review B, 2008
The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low car... more The relevance of pair-breaking by exchange and dipolar fields, and by injected spins in a low carrier density cuprate Y 1−x Pr x Ba 2 Cu 3 O 7 sandwiched between two ferromagnetic La 2/3 Sr 1/3 MnO 3 layers is examined. At low external field (H ext ), the system shows a giant magnetoresistance(MR), which diverges deep in the superconducting state. We establish a distinct dipolar contribution to MR near the switching field(H c ) of the magnetic layers. At H ext ≫ H c , a large positive MR, resulting primarily from the motion of Josephson vortices and pair breaking by the in-plane field, is seen.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1-xPrxBa2Cu3O7-δ (Pr-YBCO, 0⩽x⩽0.4 ) are reported over a broad range of temperature and magnetic-field strength. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature (Tc) . This effect is attributed to vortexlike excitations in the phase incoherent condensate existing above Tc . A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc≈110K for disorder-free YBa2Cu3O7-δ .
Applied Physics Letters, 2006
The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM prox... more The transport of quasiparticles and paired electrons across superconductor SC-ferromagnet FM proximity ef-fect junctions provides valuable information on the degree of spin polarization in the ferromagnet, exchange-field-induced inhomogeneous superconductivity at the ...
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-\delta}$(Pr-YBCO, 0$\leq x\leq$0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(T$_c$). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above T$_c$. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a T$_c\approx$110K for disorder-free YBa$_2$Cu$_3$O$_{7-\delta}$.
The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ ... more The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.
Journal of Magnetism and Magnetic Materials, 2008
The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3... more The isothermal magnetoresistance [R(θ)] of [001] and [110] epitaxial films of La 2/3 Sr 1/3 MnO 3 measured as a function of the angle θ between current ( I) and magnetic field ( H), both in the plane of the film, is measured at several temperatures between 10 and 300K. The magnetic easy axis of these polytypes is intimately related to the orientation of Mn -O -Mn bonds with respect to the crystallographic axis on the plane of the substrate and energy equivalence of some of these axes. The magnetization vector ( M ) of the [001] and [110] type films is pinned along the [110] and [001] directions respectively at low fields. A magnetization orientation phase transition (MRPT) which manifests itself as a discontinuity and hysteresis in R(ψ) where ψ is the angle between H and the easy axis for the H below a critical value H * has been established. The boundary of the pinned and depinned phase on the H-T plane has been established. The highly robust pinning of magnetization seen in [110] films is related to their uniquely defined easy axis. The isothermal resistance R ⊥ and R for I⊥ H and I H, respectively for both polytypes follows the inequality R ⊥ > R for all ranges of fields (0 ≤ H ≤ 3500Oe) and temperatures (10K -300K). A full fledged analysis of the rotational magnetoresistance is carried out in the framework of Döring theory for MR in single crystal samples. Strong deviations from the predicted angular dependence are seen in the irreversible regime of magnetization.
Physical Review B, 2007
Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−... more Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y1−xPrxBa2Cu3O 7−δ (Pr-YBCO, 0≤ x ≤0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(Tc). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above Tc. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a Tc ≈110K for disorder-free YBa2Cu3O 7−δ .