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The consequences of 50 MeV Li 3+ ion irradiation on the structural and magnetic behaviour of polycrystalline samples of spinel ferrite system Li 0.5+0.5 x Ti x Al 0.1 Fe 2.4−1.5 x O 4 are investigated by using X-ray diffraction (XRD), magnetization and 57 Fe Mossbauer spectroscopy. The Mossbauer spectra exhibit central enhancement after SHI-irradiation, which is attributed to the paramagnetic centres created due to the irradiation. The reduction observed in the saturation magnetic moment after SHI-irradiation is ascribed to the partial formation of paramagnetic centres and rearrangement of the cations in the lattice corroborated by XRD and Mossbauer Loretnzian intensity analysis. The presence of amorphous phase in the irradiated samples is ruled out.

The percentage substitution of large cation like Ca2+ for Mg2+ in MgFe2O4 without altering the cubic symmetry and its effect on structural, bulk magnetic and electrical properties have been investigated for Mg1−xCaxFe2O4 (x=0.0–0.35) spinel ferrite system by means of X-ray diffraction (XRD), magnetization, ac susceptibility and dc resistivity measurements. It is found that a maximum of 23% of Ca2+ can be substituted for Mg2+. The variation of magneton number with x can be explained on the basis of Neel’s collinear spin model. The Neel temperature determined through ac susceptibility and dc resistivity measurements agree with those calculated theoretically. The variation of electrical resistivity go hand in hand with the variation of the activation energy with the Ca-content.

The structural properties of Mg2+ and Al3+ co-substituted Li0.5Fe2.5O4 are studied by synthesizing the spinel solid solution series MgxAl2xLi0.5(1−x)Fe2.5(1−x)O4. Polycrystalline samples of this series with x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 have been prepared by double-sintering ceramic method. The structural details like: lattice constant and distribution of cations in the tetrahedral and octahedral interstitial voids have been deduced through X-ray diffraction (XRD) data analysis. The x dependence of bond length, oxygen positional parameter, site ionic radii, bulk density, porosity and shrinkages have also been determined.

The structural and bulk magnetic properties of mixed spinel ferrite system Mg x Al 2 x Li 0.5(1− x ) Fe 2.5(1− x ) O 4 ( x =0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been investigated by means of X-ray diffraction, magnetization and a.c. susceptibility measurements. The cation distribution determined through X-ray data are supported by the magnetization and susceptibility measurements. The study has revealed the strong octahedral site preference of Li + and Al 3+ as compared to Mg 2+ . It is also found that the magnetic ordering in the system is of collinear type and the variation of magnetization can be explained on the basis of Neel's collinear spin model. The Neel temperatures calculated theoretically are in good agreement to those deduced experimentally.

The structural and superconducting properties of Nd- and Ca-substituted (Nd1-xCax)(Ba2-yNdy)Cu3Oz samples prepared under identical conditions have been investigated by x-ray diffraction, resistivity, ac susceptibility and oxygen content measurements. The effect of increasing Nd concentration in NdBa2-yNdyCu3Oz lowers the carrier concentration and decreases Tc, which is attributed to magnetic pair breaking by local moments and hole filling by Nd. This suppression in Tc has been compensated by appropriate hole doping with Ca in (Nd1-xCax)(Ba2-yNdy)Cu3Oz, which shows that for a fixed Nd content at the Ba site Tc increases dramatically as the Ca content increases. For instance, in the oxide (Nd1-xCax)(Baz-yNdy)Cu3Oz, the Tc increases from 0.0 K (x = 0.0, non-superconductor) to 77.5 K (x = 0.4, compensated oxide) as the magnetic pair breaking and hole filling by Nd is nearly balanced by hole doping from Ca.

The structural and superconducting properties of (Gd 1− x − y Ca y Mo x )Ba 2 Cu 3 O z samples are investigated using X-ray diffraction, ac susceptibility, electrical resistivity and oxygen content measurements. The effect of increasing the Mo concentration in (Gd 1− x Mo x )Ba 2 Cu 3 O z changes the structure from orthorhombic to tetragonal accompanied by an increase in the normal state resistivity and decreases both the oxygen content and T c which is attributed to hole filling by Mo. The substitution of Ca for Gd in (Gd 0.85− y Ca y Mo 0.15 )Ba 2 Cu 3 O z provides proper matching between the ionic radius and valence of Gd 3+ (0.94 A) and the average ionic radius and valence of Mo 4+ (0.70 A) and Ca 2+ (0.99 A). As the Ca content increases, the T c increases from 58.5 K ( y = 0) to 86 K ( y = 0.15, compensated oxide), closer to the value of 91 K for pure GdBa 2 Cu 3 O 7−δ due to the balance between the hole filling by Mo and hole doping by Ca.

A study has been made of the linear attenuation and mass attenuation coefficients of 662 and 1170 keV gamma radiations, from 137Cs and 60Co, respectively, for varying concentrations of solutions of CoSO4-7H20. Comparison has been made with predictions, based upon the mixture rule applied to these particular solutions.

The structural and superconducting properties of CuCo and coupled ErCa CuCo substitution in ErBa2Cu3O7 − δ have been studied using X-ray diffraction, a.c. susceptibility, resistivity and oxygen content measurements. The oxides (Er1 − yCay)Ba2(Cu1 − xCox)3Oz have been synthesized for 0 ≤ x ≤ 0.15 and 0 ≤ y ≤ 0.45. The effect of increasing the Co-concentration in ErBa2(Cu1 − xCoxOz for 0 ≤ x ≤ 0.15 is to lower the carrier concentration and decrease Tc, which is attributed to the hole filling by Co. This suppression in Tc has been compensated for by appropriate hole doping with Ca, in (Er1 − yCay)Ba2(Cu1 − xCox)3Oz, which shows that for a fixed Co-content Tc increases dramatically as the Ca-content increases, leading, for instance, to the oxide (Er0.55Ca0.45)Ba2(Cu0.85Co0.15)3O6.81 (to a Tc of 71 K), whereas the non-substituted phase ErBa2(Cu0.85Co0.15)3O6.70 does not superconduct. As a result, the ‘compensated oxide’ (Er1 − yCay)Ba2(Cu − xCox)3Oz exhibits an almost x-independent Tc ranging from 86 to 84 K for 0.12 ≤ y = 3x ≤ 0.24.

The structural and superconducting properties of (Er1−yCay)Ba2 (Cu1−xCox)3Oz samples are investigated using X-ray diffraction, resistivity and oxygen content measurements. The effect of increasing Co concentration in ErBa2(Cu1−xCox)3Oz lowers the carrier concentration and decreases Tc, which is attributed to hole filling by Co. This suppression of Tc has been compensated by appropriate hole doping with Ca, for instance, in the oxide (Er1−yCay)Ba2(Cu0.94Co0.06)3Oz, the Tc increases from 34 K (y = 0.0) to 85 K (y = 0.18, compensated oxide) as the hole filling by Co is completely balanced by hole doping from Ca.

The structural and superconducting properties of (Er1−y−yCayHfx)Ba2Cu3Oz samples are investigated using X-ray diffraction, resistivity, AC susceptibility and oxygen-content measurements. The effect of increasing the Hf concentration in Er−xHfxBa2Cu3Oz lowers the oxygen content and decreases Tc which is attributed to hole filling by Hf. The substitution of Ca for Er in (Er0.85−yCayHf0.15)Ba2Cu3Oz provides a proper matching between the ionic radius and valence of Er3+ (0.88 A) and the average ionic radius and valence of Hf4+ (0.78 A) and Ca2+ (0.99 A). As the Ca content increases, the Tc increases from 70 K (y = 0.05) to 86 K (y = 0.25, compensated oxide), closer the value of 91 K for pure ErBa2Cu3O7−δ due to the balance between the hole filling by Hf and hole doping by Ca.

Pr substituted at constant Ca concentration for Y in (Y1−x−yPrxCay)Ba2Cu3O7−δ superconductors have been prepared under identical conditions and the temperature dependence of the electrical resistivity of these samples are measured. The resistively determined values of Tc decrease linearly with increasing x (0 ≤ x ≤ 0.2) for constant y = 0.10 and 0.15 which provides convincing evidence that the suppression of superconductivity by Pr is mainly due to magnetic pair breaking. The suppression of superconductivity can also be correlated to the observed changes in oxygen content determined by iodometric analysis and to the average Cu-valences. However, it is found that the observed suppression of Tc cannot be compensated by appropriate hole doping with Ca.

We have prepared and identified as a single-phase the new high- T c 2-2-3 type superconductor Y 2 Ba 1.5 Ca 0.5 Cu 3 O 8+δ by resistance and a.c.-susceptibility measurements. The resistive superconducting onset occurs at 82 K and “zero resistance” at 78 K. Diamagnetism and Meissner effect sets in at low fields and magnetic superconducting onset starts at 82 K. The systematic investigation of the real and imaginary components of a.c.-susceptibility reveals that the magnetic behavior is that of a granular type superconductor.

The magnetic properties of the spinel series Ge x Cu 1− x Fe 2 O 4 ( X = 0 to 0.8) have been investigated by means of Mossbauer spectroscopy. Mossbauer spectra for X = 0.0 to 0.6 suggest the existence of two hyperfine fields, one due to the Fe 3+ tetrahedral ions ( A -sites) and the other due to Fe 3+ octahedral ions ( B -sites), while for X = 0.8 it shows the superposition of hyperfine field split spectra from A - and B -site ions and a broad central line spectrum. For 0.2 ⩽ X ⩽ 0.4, fast electron exchange among octahedral iron ions occurs as in Fe 3 O 4 . The variations of nuclear magnetic fields at the A - and B -sites are explained on the basis of A  B and B  B supertransferred hyperfine interactions.

High temperature superconductivity was observed in the system YBa 2− x Ca x Cu 3 O 7− δ for 0 ⩽ x ⩽ 1 by means of resistance and a.c.- usceptibility measurements. It was found that 50% Ca is substituted for Ba in YBa 2 Cu 3 O 7− gd with transition temperatures at zero resistance vary between 90.0K ( x = 0) and 78.0K ( x = 1), which may be explained on the basis of deviation from linearity of resistance.

High- T c YBa 1.5 Ca 0.5 Cu 3 O 7−δ superconductor has been prepared by solid-state reaction method. Low field a.c.-magnetic properties have been measured and are explained in relation to the microstructure of the material. From the lossy component of the a.c.-susceptibility the transport critical current J c and its temperature dependence have been computed. It is concluded that the magnetic and transport behaviour is that of a granular type superconductor in which strongly superconducting grains are coupled via weak superconducting links.

Ac-susceptibility measurements at various temperatures and hysteresis studies at various fields indicate that the system Ge x Cu 1− x Fe 2 O 4 ( x ⩽ 0.6) contains mixed multidomain, single domain or superparamagnetic states. Sharp susceptibility maxmima, resembling those of spin glasses, are observed for x = 0.1 and 0.2, which may be attributed to the single domain-superparamagnetic (SDSP) transition and the overall behaviour shows a cluster spin glass type of ordering.