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In this study ultra-high molecular weight polyethylene (UHMWPE) was subject to high energy mechanical milling at different milling times (5, 10 and 15 hours). Mössbauer spectroscopy analysis revealed that iron particles, coming from the milling container, were incorporated into the polymeric matrix. It is important to study the effects that such iron contaminating particles promote in polymeric cells because the contaminated polymer may present new properties. Mössbauer spectra demonstrated clearly the formation of two paramagnetic phases, indicating that the contaminating atoms were inserted in the polymer matrix, either in a replacing or in an interstitial form in two distinct regions of the polymer.

This paper presents the physical properties of a nonstandard orthorhombic form of MnV 2 O 6 , including a comparison with the isostructural orthorhombic niobate MnNb 2 O 6 , and with the usual MnV 2 O 6 monoclinic polymorph. Orthorhombic (P bcn) MnV 2 O 6 is obtained under extreme conditions of high pressure (6.7 GPa) and high temperature (800 • C). A negative Curie-Weiss temperature θ CW is observed, implying dominant antiferromagnetic interactions at high temperatures, in contrast to the positive θ CW of the monoclinic form. Specific-heat measurements are reported down to 1.8 K for all three compounds, and corroborate the magnetic-transition temperatures obtained from susceptibility data. Orthorhombic MnV 2 O 6 presents a transition to an ordered antiferromagnetic state at T N = 4.7 K. Its magnetic structure, determined by neutron diffraction, is unique among the columbite compounds, being characterized by a commensurate propagation vector k = (0,0, 1 2). It presents antiferromagnetic chains running along the c axis, but with a different spin pattern in comparison to the chains observed in MnNb 2 O 6. By a comparative discussion of our observations in this three compounds, we are able to highlight the interplay between competing interactions and dimensionality that yield their magnetic properties.

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