*Article* **Entropy of Conduction Electrons from Transport Experiments**

#### **Nicolás Pérez 1,\*, Constantin Wolf 1,2, Alexander Kunzmann 1,2, Jens Freudenberger 1,3, Maria Krautz 4, Bruno Weise 4, Kornelius Nielsch 1,2,5 and Gabi Schierning 1**


Received: 17 January 2020; Accepted: 19 February 2020; Published: 21 February 2020

**Abstract:** The entropy of conduction electrons was evaluated utilizing the thermodynamic definition of the Seebeck coefficient as a tool. This analysis was applied to two different kinds of scientific questions that can—if at all—be only partially addressed by other methods. These are the field-dependence of meta-magnetic phase transitions and the electronic structure in strongly disordered materials, such as alloys. We showed that the electronic entropy change in meta-magnetic transitions is not constant with the applied magnetic field, as is usually assumed. Furthermore, we traced the evolution of the electronic entropy with respect to the chemical composition of an alloy series. Insights about the strength and kind of interactions appearing in the exemplary materials can be identified in the experiments.

**Keywords:** electronic entropy; Seebeck coefficient; transport; LaFeSi; FeRh; CuNi
