Magnetic and magnetocaloric properties in second-order phase transition La^sub 1-x^K^sub x^MnO^sub 3^ and their composites

In this work, we present a detailed study on the magnetic properties and the magnetocaloric effect (MCE) of La1−xKxMnO3 compounds with x=0.05–0.2. Our results pointed out that the Curie temperature (TC) could be controlled easily from 213 to 306 K by increasing K-doping concentration (x) from 0.05 to 0.2. In the paramagnetic region, the inverse of the susceptibility can be analyzed by using the Curie-Weiss law, χ(T)=C/(T−θ). The results have proved an existence of ferromagnetic clusters at temperatures above TC. Based on Banerjee's criteria, we also pointed out that the samples are the second-order phase transition materials. Their magnetic entropy change was calculated by using the Maxwell relation and a phenomenological model. Interestingly, the samples with x=0.1–0.2 exhibit a large MCE in a range of 282–306 K, which are suitable for room-temperature magnetic refrigeration applications. The composites obtained from single phase samples (x=0.1–0.2) exhibit the high relative cooling power values in a wide temperature range. From the viewpoint of the refrigerant capacity, the composites formed out of La1−xKxMnO3 will become more useful for magnetic refrigeration applications around room-temperature.