Room‐temperature magnetic entropy change in La_0.7Sr_0.3Mn_1‐xM_xO₃ (M = Al, Ti)

Abstract

PACS 75.30. Sg, 75.47.Lx Magnetic entropy change in and above the room-temperature region has been measured for La 0.7 Sr 0.3 Mn 1-x M x O 3 (M = Al, Ti) by means of magnetization measurements in magnetic fields up to 6 T. The magnetocaloric effect (MCE) becomes strongest at the Curie temperature T c that is tuned to ~300 K by the substitution of Al or Ti for Mn. While the substitution of Al for Mn drastically reduces the entropy change, it extends considerably the working temperature span and improves the relative cooling power (RCP). The MCE and RCP seem to be only lightly affected by Ti substitution. Although manganites are considered potential for magnetic refrigerants, the limitations for achieving strong MCE in the materials are also discussed.

Magnetocaloric effect and improved relative cooling power in (La0.7Sr0.3MnO3/SrRuO3) superlattices

“…On the other hand, the δT C values in superlattices with n = 1 and 3 are larger compared to polycrystalline La 0.7 Sr 0.3 MnO 3 . As a result, the − S max M values derived from equation ( 1) are comparable with the largest − S max M values of La 0.7 Sr 0.3 MnO 3 reported in [16]. In consideration of the larger δT FWHM values, it is understood that the RCP values derived from equation ( 2) for superlattices with n = 1 and 3 are significantly improved with respect to the polycrystalline LSMO.…”

“…In the case of a very thin SRO layer corresponding to superlattices with n = 1 and 3, both ZFC and FC magnetization significantly decrease below 100 K suggesting that the stoichiometric FM SRO layers are not fully formed. The magnetization values, recorded in a field of 50 Oe below T C , are much higher in our superlattices than those (≈9 emu g −1 ) in a field of 100 Oe reported in polycrystalline LSMO [16], which is ascribed to enhanced magnetization (see below) and the in-plane direction of the easy axis [9]. When one compares this to polycrystalline LSMO [16], it can also be seen that all the superlattices undergo a smoother paramagnetic (PM) to ferromagnetic (FM) transition, i.e.…”

“…The magnetization values, recorded in a field of 50 Oe below T C , are much higher in our superlattices than those (≈9 emu g −1 ) in a field of 100 Oe reported in polycrystalline LSMO [16], which is ascribed to enhanced magnetization (see below) and the in-plane direction of the easy axis [9]. When one compares this to polycrystalline LSMO [16], it can also be seen that all the superlattices undergo a smoother paramagnetic (PM) to ferromagnetic (FM) transition, i.e. with a larger temperature interval between PM and FM states (named δT C here) due to the higher nanostructural disorder [5].…”

“…With decreasing temperature, a sharp increase of magnetization is observed below T C = 325 K, due to the onset of ferromagnetic (FM) order in the LSMO layers. This reduced T C compared to polycrystalline LSMO (365 K) [16] is ascribed to the finite size effect in superlattices [4,13,14] and is found to be almost independent of n values (i.e. the number of SrRuO 3 layers).…”

Influence of Non-magnetic Ti4+ Ion Doping at Mn Site on Structural, Magnetic, and Magnetocaloric Properties of La0.5Pr0.2Sr0.3Mn1−xTixO3 Manganites (x = 0.0 and 0.1)

“…Figure 11a, b for temperature below and above the transition respectively for La 0.5 Pr 0.2 Sr 0.3 MnO 3 , it is viewed that | S M |changes to a positive value with the increase of the magnetic field, which corresponds to the magnetic transition from FM to PM states. We can see on Table 6 that we have a low S max M compared with the other manganites listed in the table, but we have a large full width at half maximum and consequently important RCP [29,30,33].…”