Sadia Manzoor

Interfacial spin order in exchange biased systems

The phenomenon of exchange bias in which a ferromagnet is grown in intimate contact with an antiferromagnet leads to a shifted hysteresis loop. All analytical theories developed to explain this effect predict values of the shift of the loop that are too large, often by an order of magnitude. In many numerical models an interface exchange coupling constant C∗ is introduced to account for these discrepancies. In this work we describe a series of experiments, which reveals the temperature and field dependence of this interfacial spin order that account for the weakened coupling between the layers. We also show that this order has a marked temperature dependence at temperatures down to ∼50 K. At temperatures below 50 K we observe a sudden marked increase in the observed exchange bias of up to a factor of 2, which we attribute to a spontaneous spin ordering of the interfacial spins analogous to that which occurs in spin-glass systems.

Study of Magnetothermal Properties of Strontium Doped Lanthanum Manganite Nanoparticles for Hyperthermia Applications

Magnetic nanoparticles of strontium doped lanthanum manganite (LSMO) have been synthesized with Sr concentration x = 0.20 and 0.27 using the citrate gel technique. Magnetic and magnetothermal properties have been investigated with the objective of determining their specific absorption rates (SARs) and comparing them with those obtained using the linear response theory. Adiabatic magnetothermia measurements were carried out in an RF magnetic field of 800 A/m and 214 kHz. Both magnetic and thermomagnetic behaviors of the LSMO nanoparticles are observed to be governed by the strontium content of the samples. The specific absorption rate has been determined using experimental data and good quantitative agreement has been observed between experimentally determined and theoretically derived values. Zero-field-cooled thermal demagnetization measurements were used to obtain the Curie temperature TC, which was found to be 320 K for x = 0.20 and 350 K for x = 0.27. The suitability of these materials for magnetic hyperthermia and self-controlled hyperthermia applications has been demonstrated.

Giant room temperature magnetoelectric response in strain controlled nanocomposites

We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (∼0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α = μ o d M / d E calculated from remnant magnetization at room temperature is 2.6 × 10−...