Ni Fe ∕ Fe Mn ∕ Ni Fe trilayer structure forms an integral part of many conventional and tunneling magnetoresistance spin valve structures with FeMn antiferromagnetic layer. A systematic investigation of the exchange bias variations of the seed and top pinned NiFe layers in the NiFe∕FeMn∕NiFe trilayer structure is reported as a function of thickness of all the three constituting layers, in multilayers prepared by rf magnetron sputtering. X-ray diffraction patterns show the (111) texture for the NiFe and FeMn layers, necessary for the development of antiferromagnetic γ-fcc phase. In thickness variation studies of all the three magnetic layers, seed NiFe layer shows greater bias (150Oe) than the top pinned NiFe layer (80Oe only). The exchange bias shows the expected 1∕t behavior for increasing NiFe layer thickness after initial maxima at low thickness. In the FeMn antiferromagnet layer thickness variation on the other hand, the large bias values attained around 5nm thickness is nearly retained up to a thickness of 25nm and the bias for the top NiFe layer is again substantially lower. The greater bias observed for the seed NiFe layer in all the three thickness variation studies is attributed to its growth over a saturated (111) oriented NiFe seed layer, which induces formation of interfacial FeMn layers with a net parallel spin ordering, in presence of the constant applied field. On the other hand, at the top FeMn∕NiFe surface, the rigid FeMn surface with compensated bulk spin ordering formed already, is not easily biased and reoriented along the top NiFe layer, to develop as much parallel net spins in the antiferromagnetic material, and hence lower bias.

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Ultrafine rare-earth iron garnets, (R3Fe50t2 where R = Sm, Tb, Dy, Ho, Er, Yb, (YGd), and (YNd)) have been prepared by thermal decomposition of a citrate precursor, R3Fe5(cit)zs -(36 + n)H20. The precursors decompose at lower temperatures, below 450"C, and are characterized using DTA, DSC, TG, and IR spectroscopy. Ultrafine amorphous garnets having particle size 10 to 35 nm and surface area 30 to 75 m2/g have been obtained and characterized by XRD, TEM, Mossbauer spectra, particle size analysis, and magnetic and surface area measurements. Superparamagnetism indicates the ultrafine characteristics of the garnet materials. The nature of crystallite aggregates and agglomerates is of special interest because it represents finite clusters. An intercrystallite bond exists between crystallites having 1.0-to 1.5-nm size. The rupture of intercrystallite bonds during crystallization leads to monolith formation.[

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