Magnetic-field suppression of thermoelectricity in a metallic frustrated magnet

The thermoelectric effect (TE) in metals occurs as a voltage difference – accumulated charge – when a thermal gradient is applied. This property can be used to convert heat into electrical energy in power generation and in temperature sensing. Among several scattering mechanisms, TE depends on how the charge carriers interact with any underlying magnetic structure. In a publication in Physical Review Letters, scientists at the HFML and Radboud University, together with colleagues from POSTECH in Korea, have demonstrated that TE in a metallic frustrated magnet can be completely suppressed by applying high magnetic fields of 30 T.

The investigated material PdCrO2 consists of alternating layers of conducting and magnetic ions whose interaction can lead to novel phenomena. At high temperatures, the charge carriers scatter principally off quantized waves called magnons which are created by thermally exciting the spins on the magnetic ions. This mechanism is strongly suppressed by a magnetic field, leading to the reduction in the thermoelectric voltage. With lowering temperature, this ‘frustrated’ magnetic structure becomes stiffer. Finally, it orders in a compromising manner with an angle of 120° between its moments to satisfy the underlying triangular lattice. The new magnetic order leads to the TE being more resilient to an applied field.

Figure 1

Figure 2

The observed phenomena are evidence of an interesting symbiosis between the spin and charge excitations in this system and suggests that magnetic-field tuning of the TE coefficient in certain frustrated magnets could lead to improvements in the thermal management of electronic and magnetic devices.

Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet 
S. Arsenijević, J.M. Ok, P. Robinson, S. Ghannadzadeh, M. I. Katsnelson, J.S. Kim, and N. E. Hussey, Physical Review Letters 116, 087202 (2016)