The effect of Mn substitution on ferroelectric and antiferromagnetic properties of the Bi0.9La0.1Fe1−xMnxO3 system has been studied. It is seen that, with the increase in Mn content, there is a contraction in unit cell volume. Since the cell volume contraction is isotropic, lattice distortion (c/a) remains the same and so is the ferroelectric transition temperature TC. Further, it is observed that the presence of Mn does not affect the loss tangent (tan δ) of the samples. On the contrary, with increase in Mn content, a small but linear enhancement in the magnetization is observed.

A spin glass state is observed in the double perovskite oxide Sr 2 FeCoO 6 prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a ¼ 5.4609(2) Å and c ¼ 7.7113(7) Å . The temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr 2 FeCoO 6 , the B site is randomly occupied by Fe and Co in the mixed valence states of Fe 3 þ /Fe 4þ and Co 3þ /Co 4þ . The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass state in this double perovskite, which is observed as an irreversibility in temperature dependent dc magnetization at T f $ 75 K. Dynamical scaling analysis of v 0 (T) yields a critical temperature T ct ¼ 75.14(8) K and an exponent z ¼ 6.2(2) typical for spin glasses. The signature of presence of mixed magnetic interactions is obtained from the thermal hysteresis in magnetization of Sr 2 FeCoO 6 . Combining the neutron and magnetization results of Sr 2 FeCoO 6 , we deduce that Fe is in low spin state while Co is in both low spin and intermediate spin states. V

Magnetoelectrics, characterized by simultaneous ferroelectric and magnetic ordering, have potential applications in information storage, sensors, etc. However, there are very few materials exhibiting the coexistence of ferroelectric and ferromagnetic ordering at room temperature. Hence, in normal practice, desired magnetoelectric effect is achieved by growing heterostructures of ferroelectric and magnetic materials. Realization of heterostructures with desired properties is not only difficult but also involves complicated lengthy procedures. BiFeO3 is weakly ferroelectric and antiferromagnetic at and above room temperature. We have been successful in enhancing both the ferroelectric and the magnetic properties of BiFeO3 by partial substitution of Tb at Bi site. Thin films of Bi0.6Tb0.3La0.1FeO3, integrated on Si/SiO2/TiO2/Pt substrate by using pulsed laser deposition technique, show good ferroelectric and magnetic properties and also coupling between them. Single step growth of thin films with desired magnetoelectric properties is certainly a cost effective, reliable, and simple alternative to heterostructures.

In the present investigation, we report a systematic study of Ag admixing in MgB 2 prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/ microstructural characterization employing x-rays diffraction (XRD) and transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by physical property measurement system (PPMS). The TEM investigations reveal the formation of MgAg nanoparticles in Ag admixed samples. These nanoparticles may enhance critical current density due to their size (~ 5-20 nm) compatible with coherence length of MgB 2 (~ 5-6 nm) . In order to study the flux pinning effect of Ag admixing in MgB 2 , the evaluation of intragrain critical current density (J c ) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on intragrain J c is obtained for 10 at.% Ag admixed sample at 5K. This corresponds to ~9.23 x 10 7

Magnetization vs temperature behavior of RuSr2GdCu2O8−δ (Ru-1212) measured in an field of 5 Oe, shows a clear branching of zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, a cusp at 135 K, and a diamagnetic transition around 20 K (in the ZFC branch). The cusp at 135 K is due to the antiferromagnetic ordering of the Ru moments. The magnetization-field isotherms, below 50 K, show a nonlinear contribution from a ferromagnetic component. The resistance vs temperature behavior of the compound, in applied fields of 0, 3, and 7 T, confirms that the sample is superconducting at around 20 K. The superconducting transition exhibits field broadening of a type different than that known for conventional high Tc superconductors. The magnetoresistance (MR) is negative above the Ru magnetic ordering temperature of 135 K, while below this temperature, MR displays a positive peak in low fields and becomes negative in higher fields. A maximum of 2% is observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction pattern obtained for this Ru-1212 sample shows two types of superstructure; one with a weak spot at the center of the a–b rectangle and the other only along the b direction. It is possible that either Ru/Cu or Ru4+/Ru5+ ordering of 2b periodicity takes place along the b direction.

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Abstract. We study the nonlinear dynamics of normal field instability in a ferrofluid under the influence of a uniform magnetic field. In addition, a small normal sinusoidal magnetic field is superimposed on the system. An equation governing the evolution of small but finite amplitude is obtained. Applying the Melnikov method, it is shown that there exist transverse homoclinic orbits leading to chaotic motions.