We report the results of dc resistivity, ac susceptibility, and thermopower study of partial substitution at Y (A site by Ca) and at Cu (B site by Ni) polycrystalline superconductors. The iodometric analysis reveals t...We report the results of dc resistivity, ac susceptibility, and thermopower study of partial substitution at Y (A site by Ca) and at Cu (B site by Ni) polycrystalline superconductors. The iodometric analysis reveals that the oxygen deficiency,δ,for YBa2Cu3O7-δ(S-I),Y0.9Ca0.1 Ba2Cu3O7-δ(S-II),Y0.8Ca0.2Ba2Cu3O7-δ(S-III) and Y0.9Ca0.1 Ba2(Cu0.99Ni0.01)3O7-δ(S-IV) samples are 0.16, 0.30, 0.39 and 0.29 respectively. The x-ray powder diffraction pattern indicates that all samples are in orthorhombic phase. The dc resistivity, ac susceptiblity and the thermopower measurements shows that the divalent Calcium doping at the trivalent Y site and transition metal Ni doping at Cu site causes a suppression of the superconducting transition temperature (Tc) from 89 to 81 K. The ac susceptibility confirms the ferromagnetic to antiferromagnetic phases at a defined Tc. The room temperature S value increases for Ca substituted YBa2Cu3O7-δwhile to that it decreases for Y0.9Ca0.1Ba2(Cu0.99Ni0.01)3O6.71. The above feature is an indicative of enhanced number of mobile holes for the Ca doped YBa2Cu3O7-δ, while to that the charge carrier density is reduced in simultaneous A (Ca) and B (Ni) site doped sample.展开更多
Magnetic properties and magnetic structure of the Ba_(2)Mn(PO_(4))_(2) antiferromagnet featuring frustrated zigzag chains of S?52 Mn^(2+)ions are reported based on neutron diffraction,density-functional bandstructure ...Magnetic properties and magnetic structure of the Ba_(2)Mn(PO_(4))_(2) antiferromagnet featuring frustrated zigzag chains of S?52 Mn^(2+)ions are reported based on neutron diffraction,density-functional bandstructure calculations,as well as temperature-and field-dependent measurements of magnetization and specific heat.A magnetic transition at TN■5 K marks the onset of the antiferromagnetic order with the propagation vector k=(1/2 0 1/2)and the ordered moment of 4.33±0.08μB/Mn^(2+)at 1.5 K,pointing along the c direction.The direction of the magnetic moment is chosen by single-ion anisotropy,which is relatively weak compared to the isostructural Ni^(2+)compound.Geometrical frustration has a strong impact on the thermodynamic properties of Ba_(2)Mn(PO_(4))_(2),but manifestations of the frustration are different from those in Ba_(2)Ni(PO_(4))_(2),where frustration by isotropic exchange couplings is minor,yet strong and competing single-ion anisotropies are present.A spin-flop transition is observed around 2.5 T.The evaluation of the magnetic structure from the ground state via the spin-flop state to the field-polarized ferromagnetic state has been revealed by a comprehensive neutron diffraction study as a function of magnetic field below TN.Finally,a magnetic phase diagram in the H-T plane is obtained.展开更多
Solid-state ceramic technique route is used for synthesizing Cr-doped haematiteaα-Fe_(2-x)Cr_(x)O_(3)(x=0,0.125,0.50 and 1)samples.Single phase and corundum(Al2O_(3))type structure is revealed from the X-ray diffract...Solid-state ceramic technique route is used for synthesizing Cr-doped haematiteaα-Fe_(2-x)Cr_(x)O_(3)(x=0,0.125,0.50 and 1)samples.Single phase and corundum(Al2O_(3))type structure is revealed from the X-ray diffraction(XRD)patterns.The Raman spectra ofαa-Fe_(2-x)Cr_(x)O_(3)illustrate seven phonon modes.On substitution of Cr(x=0,0.125,0.50 and 1)at Fe site,all Raman active modes are shifted to higher wave numbers.The coercivity and remanence of Cr-doped haematites increase as x increases.The increased coercivity and remanence for Cr-doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy.The observed isomer shiftδdvalues from room-temperature Mössbauer data clearly show the presence of ferric(Fe^(3+))and Cr^(3+)ions illustrating strong ferromagnetic ordering up to x=0.125 inaα-Fe_(2-x)Cr_(x)O_(3)haematite and weak ferromagnetic ordering foraα-Fe2-xCrxO_(3)(x>0.125)haematites.展开更多
Ti doped hematitea-Fe_(2-x)Ti_(x)O_(3)(x=0.0,0.0206 and 0.0344)samples are synthesized using solid-state ceramic route technique.Single phase and corundum(Al_(2)O_(3))type structure is revealed from the X-ray diffract...Ti doped hematitea-Fe_(2-x)Ti_(x)O_(3)(x=0.0,0.0206 and 0.0344)samples are synthesized using solid-state ceramic route technique.Single phase and corundum(Al_(2)O_(3))type structure is revealed from the X-ray diffraction(XRD)pattern.On substitution of Ti at Fe site,all Raman active modes are shifted to higher wave numbers.An additional feature of Eu(LO)mode at about 660 cm^(-1)is observed.The E_(u) mode frequency is decreased and pronounced systematically as a function of Ti doping,and it reaches a value of 658 cm^(-1)for x=0.0344.The coercivity Hc(remanence M_(r))for x=0.0,0.0206 and 0.0344 are determined to be 995 Oe(0.44 emu/mg),1404 Oe(0.00019 emu/mg)and 2023 Oe(0.00016 emu/mg),respectively.The larger coercivity for Ti doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy.The observed isomer shift(d)from room temperature Mössbauer data clearly shows the presence of ferric(Fe^(3+))and Ti^(4+)ordering ofa-Fe_(2-x)Ti_(x)O_(3)for x=0.0344.展开更多
文摘We report the results of dc resistivity, ac susceptibility, and thermopower study of partial substitution at Y (A site by Ca) and at Cu (B site by Ni) polycrystalline superconductors. The iodometric analysis reveals that the oxygen deficiency,δ,for YBa2Cu3O7-δ(S-I),Y0.9Ca0.1 Ba2Cu3O7-δ(S-II),Y0.8Ca0.2Ba2Cu3O7-δ(S-III) and Y0.9Ca0.1 Ba2(Cu0.99Ni0.01)3O7-δ(S-IV) samples are 0.16, 0.30, 0.39 and 0.29 respectively. The x-ray powder diffraction pattern indicates that all samples are in orthorhombic phase. The dc resistivity, ac susceptiblity and the thermopower measurements shows that the divalent Calcium doping at the trivalent Y site and transition metal Ni doping at Cu site causes a suppression of the superconducting transition temperature (Tc) from 89 to 81 K. The ac susceptibility confirms the ferromagnetic to antiferromagnetic phases at a defined Tc. The room temperature S value increases for Ca substituted YBa2Cu3O7-δwhile to that it decreases for Y0.9Ca0.1Ba2(Cu0.99Ni0.01)3O6.71. The above feature is an indicative of enhanced number of mobile holes for the Ca doped YBa2Cu3O7-δ, while to that the charge carrier density is reduced in simultaneous A (Ca) and B (Ni) site doped sample.
文摘Magnetic properties and magnetic structure of the Ba_(2)Mn(PO_(4))_(2) antiferromagnet featuring frustrated zigzag chains of S?52 Mn^(2+)ions are reported based on neutron diffraction,density-functional bandstructure calculations,as well as temperature-and field-dependent measurements of magnetization and specific heat.A magnetic transition at TN■5 K marks the onset of the antiferromagnetic order with the propagation vector k=(1/2 0 1/2)and the ordered moment of 4.33±0.08μB/Mn^(2+)at 1.5 K,pointing along the c direction.The direction of the magnetic moment is chosen by single-ion anisotropy,which is relatively weak compared to the isostructural Ni^(2+)compound.Geometrical frustration has a strong impact on the thermodynamic properties of Ba_(2)Mn(PO_(4))_(2),but manifestations of the frustration are different from those in Ba_(2)Ni(PO_(4))_(2),where frustration by isotropic exchange couplings is minor,yet strong and competing single-ion anisotropies are present.A spin-flop transition is observed around 2.5 T.The evaluation of the magnetic structure from the ground state via the spin-flop state to the field-polarized ferromagnetic state has been revealed by a comprehensive neutron diffraction study as a function of magnetic field below TN.Finally,a magnetic phase diagram in the H-T plane is obtained.
基金Authors are thankful to UGC New Delhi for financial assistance
文摘Solid-state ceramic technique route is used for synthesizing Cr-doped haematiteaα-Fe_(2-x)Cr_(x)O_(3)(x=0,0.125,0.50 and 1)samples.Single phase and corundum(Al2O_(3))type structure is revealed from the X-ray diffraction(XRD)patterns.The Raman spectra ofαa-Fe_(2-x)Cr_(x)O_(3)illustrate seven phonon modes.On substitution of Cr(x=0,0.125,0.50 and 1)at Fe site,all Raman active modes are shifted to higher wave numbers.The coercivity and remanence of Cr-doped haematites increase as x increases.The increased coercivity and remanence for Cr-doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy.The observed isomer shiftδdvalues from room-temperature Mössbauer data clearly show the presence of ferric(Fe^(3+))and Cr^(3+)ions illustrating strong ferromagnetic ordering up to x=0.125 inaα-Fe_(2-x)Cr_(x)O_(3)haematite and weak ferromagnetic ordering foraα-Fe2-xCrxO_(3)(x>0.125)haematites.
文摘Ti doped hematitea-Fe_(2-x)Ti_(x)O_(3)(x=0.0,0.0206 and 0.0344)samples are synthesized using solid-state ceramic route technique.Single phase and corundum(Al_(2)O_(3))type structure is revealed from the X-ray diffraction(XRD)pattern.On substitution of Ti at Fe site,all Raman active modes are shifted to higher wave numbers.An additional feature of Eu(LO)mode at about 660 cm^(-1)is observed.The E_(u) mode frequency is decreased and pronounced systematically as a function of Ti doping,and it reaches a value of 658 cm^(-1)for x=0.0344.The coercivity Hc(remanence M_(r))for x=0.0,0.0206 and 0.0344 are determined to be 995 Oe(0.44 emu/mg),1404 Oe(0.00019 emu/mg)and 2023 Oe(0.00016 emu/mg),respectively.The larger coercivity for Ti doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy.The observed isomer shift(d)from room temperature Mössbauer data clearly shows the presence of ferric(Fe^(3+))and Ti^(4+)ordering ofa-Fe_(2-x)Ti_(x)O_(3)for x=0.0344.
