We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe 3 O 4 /Co 1−x Zn x Fe 2 O 4 nanoparticles (0 ≤ x ≤ 1). Adjusting the magnetic anisotropy through the content of Co 2+ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response. * winkler@cab.cnea.gov.ar 1 arXiv:2005.10771v1 [cond-mat.mes-hall] 21 May 2020

Superfluid Helium, a state of matter existing at low temperatures, shows many remarkable properties. One example is the so called Fountain Effect, where a heater can produce a jet of helium. This converts heat into mechanical motion; a machine with no moving parts, but working only below 2 K. Allen and Jones first demonstrated the effect in 1938, but their work was basically qualitative. We now present data of a quantitative version of the experiment. We have measured the heat supplied, the temperature and the height of the jet produced. We also develop equations, based on the two fluid model of Superfluid Helium, that give a satisfactory fit to the data. The experiment has been performed by advanced undergraduate students in our home institution, and illustrates in a vivid way some of the striking properties of the superfluid state.

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