Water has many unusual properties: it has relatively high melting and boiling points for a small molecule, and the liquid state can also be denser than the solid state. These properties are thought to arise from the 3D network of hydrogen bonds in the molecule.

Recently, it was discovered that the near infrared spectrum and refractive index of water can be affected by a strong magnetic field. Some researchers have suggested that the magnetic field somehow strengthens hydrogen bonds, but the exact mechanism behind these results remains a mystery.

Inaba and co-workers measured the melting temperatures of ordinary water and heavy water - in which the hydrogen atoms are replaced by deuterium - with a highly sensitive differential scanning calorimeter (DSC). The changes in the melting points observed with the DSC were proportional to the square of the magnetic field, and also about three orders of magnitude larger than those calculated using the so-called magneto-Clapeyron equation.

"Since water is diamagnetic, it should not be affected by a magnetic field," Inaba told PhysicsWeb. "We believe that the thermal motion of the partially charged atoms in the water gives rise to a Lorentz force when a magnetic field is applied. By suppressing the thermal motion, the Lorentz force makes the hydrogen bonds stronger, which could account for the increase in the melting points."

The Chiba team now plans to investigate the effect of magnetic fields on phase transitions in other diamagnetic materials including gallium, indium, mercury and benzene.