  The Peltier coefficient describes the amount of heat that is carried by an
electrical current when it passes through a material. Connecting two materials
with different Peltier coefficients causes a net heat flow towards or away from
the interface, resulting in cooling or heating at the interface - the Peltier
effect. Spintronics describes the transport of charge and angular momentum by
making use of separate spin-up and spin-down channels. Recently, the merger of
thermoelectricity with spintronics has given rise to a novel and rich research
field named spin caloritronics. Here, we report the first direct experimental
observation of refrigeration/heating driven by a spin current, a new spin
thermoelectric effect which we call the spin Peltier effect. The heat flow is
generated by the spin dependency of the Peltier coefficient inside the
ferromagnetic material. We explored the effect in a specifically designed spin
valve pillar structure by measuring the temperature using an electrically
isolated thermocouple. The difference in heat flow between the two magnetic
configurations leads to a change in temperature. With the help of 3-D finite
element modeling, we extracted permalloy spin Peltier coefficients in the range
of -0.9 to -1.3 mV. These results enable magnetic control of heat flow and
provide new functionality for future spintronic devices.
