Thermal conductivity of the spin ladder material La₅Ca₉Cu₂₄O₄₁, measured parallel and perpendicular to the ladders [3].

About five years ago and in agreement with theoretical predictions [1], a new highly efficient mode of thermal conduction was discovered, namely heat transport by magnetic excitations in quasi one-dimensional insulating materials [2,3]. The magnetic conduction is highly anisotropic, dwarfing the usual lattice contribution (by up to a factor of 50, c.f. Figure 1) and has mostly been studied in novel transition metal oxides with one-dimensional spin structures such as the spin chain materials Sr₂CuO₃ and SrCuO₂ and the "ladder" compound (La,Sr,Ca)₁₄Cu₂₄O₄₁. The crucial point of this project is that around room temperature the magnetic heat conductivity κ_mag (of the order of 100 Wm^-1K^-1) is as efficient as metallic heat conduction. However, compared to conventional materials with high thermal conductivity these novel compounds offer the following advantages:

• They are electrically insulating and can therefore be used to simultaneously electrically insulate electronic circuits and carry away heat.
• Heat is conducted primarily along one crystal axis, hence the material can carry away heat in one direction and insulate along the others.
• Heat is carried by localized spins which can be manipulated with magnetic fields or light. Therefore, for the first time an electrical insulator with tunable heat conductivity at room temperature could emerge.

Scientific and Technological Objectives and Innovation

The main objective of this project is to provide the scientific and technological knowledge which is necessary to exploit these materials for advanced and innovative thermal management. A successful project outcome will result in the fabrication of two testing devices. The first device will show that the large anisotropic thermal conductivity of these novel oxide materials will allow to efficiently channel away parasitic heat such as that generated in integrated semiconductor circuits. The second device will combine the properties of the first device with tunable heat conduction, thereby allowing for "smart cooling" or local temperature regulation.