Pressure Tuning of Magnetism and Drastic Increment of Thermal Conductivity under Applied Magnetic Field in HgCr_2S_4

HgCr2S4 is a typical compound manifesting competing ferromagnetic （FM） and antiferromagnetic （AFM） exchanges as well as strong spin-lattice coupling. Here we study these effects by intentionally choosing a combination of magnetization under external hydrostatic pressure and thermal conductivity at various magnetic fields. Upon applying pressure up to 10 kbar at 1 kOe, while the magnitude of magnetization reduces progressively, the AFM ordering temperature TN enhances concomitantly at a rate of about 1.5 K/kbar. Strikingly, at lO kOe the field polarized FM state is found to be driven readily back to an AFM one even at only 5kbar. In addition, the thermal conductivity exhibits drastic increments at various fields in the temperature range with strong spin fluctuations, reaching about 30% at 50 kOe. Consequently, the results give new experimental evidence of spin-lattice coupling. Apart from the colossal magnetoeapacitance and colossal magnetoresistance reported previously, the findings here may enable new promising functionalities for potential applications.

Analysis of periodic pulsating nanofluid flow and heat transfer through a parallel-plate channel in the presence of magnetic field

In this paper,we focus on the two-dimensional pulsating nanofluid flow through a parallel-plate channel in the presence of a magnetic field.The pulsating flow is produced by an applied pressure gradient that fluctuates with a small amplitude.A kind of proper transformation is used so that the governing equations describing the momentum and thermal energy are reduced to a set of non-dimensional equations.The analytical expressions of the pulsating velocity,temperature,and Nusselt number of nanofluids are obtained by the perturbation technique.In the present study,the effects of the Cu-H2O and Al_(2)O_(3)-H2O nanofluids on the flow and heat transfer in pulsating flow are compared and analyzed.The results show that the convective heat transfer effect of Cu-H2O nanofluids is better than that of Al_(2)O_(3)-H2O nanofluids.Also,the effects of the Hartmann number and pulsation amplitude on the velocity,temperature,and Nusselt number are examined and discussed in detail.The present work indicates that increasing the Hartmann number and pulsation amplitude can enhance the heat transfer of the pulsating flow.In addition,selecting an optimal pulsation frequency can maximize the convective heat transfer of the pulsating flow.Therefore,improved understanding of these fundamental mechanisms is conducive to the optimal design of thermal systems.

Corrosion behavior of Al-3.0 wt%Mg alloy in NaCl solution under magnetic field

The influences of applied magnetic field on the corrosion behavior of Al-3.0 wt%Mg alloy in 3.5 wt% NaCl solution were investigated by electrochemical measurements,scanning electron microscopy（SEM）and energy-dispersive spectroscopy（EDS）.Stochastic analysis was applied to investigate the influences of applied magnetic field.The results indicate that the application of horizontal magnetic field of 0.4 T would increase the pitting corrosion potential（E_（pit））,decrease the corrosion current density（i_（corr））,prolong the pit initiation time,slow down the pit generation rate and inhibit the growth of pitting of the tested alloys in 3.5 wt% NaCl solution.The applied magnetic field would also change the mechanism of pit initiation of Al-3.0 wt%Mg alloy from A_3 model（without magnetic field）to A_3＋A_4 model（with magnetic field）.The intermediate product Al_（（ad））~＋ is the paramagnetic ion that would be influenced by magnetic field sensitively.