Theoretically, a thermal rectifier is a solid state device which presents a greater heat flux in the forward than in the reverse thermal bias, Q+ > Q−. Ferromagnetic materials, which can exist in two magnetic states with distinct thermal conductivities, provide a unique opportunity to realize nonlinear thermal transport. Herein, by realizing a proof-of concept device consisting of manganites type La1-xSrxMnO3, we introduce a two-segment thermal diode that manipulates the heat via a sequential deactivation of magnons in each segment through their respective Curie temperatures Tc. Thermal measurements of the diode show that as the sequential magnetic transitions occur, the rectification factor increases. We interpret such an enhancement in the rectification factor due to drastic changes in the thermal conductance of the device as a consequence of the spin-disorder dominance above Tc. Furthermore, the results are validated via an analytical model within the framework of the Fourier law by using power law approximations of the temperature-dependent thermal conductivity of segments. Hence, sequential deactivation of magnons provides an alternative route so as to develop enhanced performance thermal rectifiers.

In an ideal model, a thermal rectifier is the thermal equivalent of the electrical diode. A device which leads a greater heat flow in one direction than another one. Currently used bulk and molecular mechanisms which can potentially result in thermal rectifying behavior have not evidenced that the rectification factor can reach one order of magnitude, which is an arbitrary limit required to deem the effect useful for engineered systems. Here, we have succeeded in building thermal diodes with thermal rectification factors up to 1.62 under 29 K temperature bias. Devices manipulate heat via the activation and deactivation of magnons in magnetic materials at room temperature through the Curie temperature. Furthermore, this factor can be enhanced further by improving the magnetic properties in the material and by increasing the thermal bias. In addition, thermal diodes present a well-defined breakdown as well as forward temperatures which control accurately the on state of the device. This approach paves the way to pursuit the one order limit at room temperature in a simple way and opens a new route towards the next generation of thermal devices.

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Thermal impedance Zth(iω) is a way of defining the thermophysical characteristics and behavior of thermal systems. Existing photoacoustic and photothermal approaches based on thermal impedance formalism merely allows a partial thermal characterization of the materials (generally, either thermal diffusivity or thermal effusivity). In this work, a new approach based on the thermal impedance concept in terms of its characteristic thermal time constant is developed from thermal quadrupoles formalism. The approach outlined in this contribution presents a set of analytical equations in which through a single measurement of thermal impedance is sufficient to obtain a comprehensive characterization of the thermophysical properties of solid materials in a simple way.