A new type of material can change from solid to liquid in response to an alternating magnetic field. The material has a wide range of potential uses, and its creators have demonstrated how it might be applied in electronic circuitry, drug delivery and for fastening objects in confined spaces. They even used it to make a Lego man capable of melting, breaking out of a prison cell and reforming in a dramatic scene reminiscent of the 1991 sci-fi classic Terminator 2.

The magnetoactive phase transitional matter (MPTM) is made of magnetic neodymium–iron–boron microparticles embedded within a gallium matrix. It heats up and undergoes a phase change from solid to liquid when exposed to an alternating magnetic field, and resolidifies when cooled.

The China and US-based team behind the work says that the temperature at which MPTMs melt can be tuned for different applications by using other liquid metals, for example gallium alloys, as the matrix material.

To demonstrate some of the different ways that MPTMs might be used, the researchers used magnetic fields to bring about solid-to-liquid transitions and manoeuvre the material into various positions.

Given the high strength of the material when in solid form, the researchers suggest it could be used as a universal screw for use in confined spaces. To illustrate this, they manipulated the material into position over a difficult-to-reach threaded screw hole, melted it to fill the cavity and then resolidified it to fasten two plastic plates together. The researchers also used the material to solder an LED circuit by remote control and to retrieve objects from inside a replica of a human stomach.

In their most visually striking demonstration, the researchers used magnetic fields to break an MPTM Lego man out of jail. They first melted the model then manoeuvred the liquid material out of a cage and into a mould where it was recast into its original shape when it cooled.