http://www.nature.com/news/2001/010612/full/news010614-6.html
*Stiff challenge to spacetime* A strong magnetic field can flatten space time by imposing a 1 dimensional character on the three dimensional vacuum by aligning the vacuum along straight intense magnetic field lines. What this effectively accomplishes is reduces the intensity of space warping imposed on spacetime by the concentration of matter as defined by general relativity. It follows that a strong magnetic field will reduce the gravity field that a mass imposes on spacetime (aka anti-gravity).
