Conventional and inverse magnetocaloric effects in La0.45Sr0.55MnO3 nanoparticles

Abstract

The magnetocaloric effect of La 0.45 Sr 0.55 MnO 3 nanoparticles was studied by dc magnetization measurements. A sample with mean particle size of about 140 nm exhibits both a conventional magnetocaloric effect around the Curie temperature (% 295 K) and a large inverse magnetocaloric effect around the antiferromagnetic-ferromagnetic transition temperature (% 200 K). The change of magnetic entropy increases monotonically with applied magnetic field and reaches the values of 5.51 J/kg K and À 2.35 J/kg K at 200 K and 295 K, respectively, in an applied field of 5 T. The antiferromagnetic-ferromagnetic transition is absent in a 36 nm size sample, which shows only a broad ferromagnetic transition around 340 K and a small change in magnetic entropy near room temperature. The results are discussed in terms of the entropy difference between the A-type antiferromagnetic ground state of La 0.45 Sr 0.55 MnO 3 and the low moment ferromagnetic state. By comparing the results obtained on nanoparticles and bulk La 0.45 Sr 0.55 MnO 3 , one can conclude that the inverse magnetocaloric effect in a material showing the antiferromagnetic-ferromagnetic transition could be improved over a wide range of temperature by tuning the spin disorder in the antiferromagnetic state.

Magnetic properties, exchange bias, and memory effects in core-shell superparamagnetic nanoparticles of La0.67Sr0.33MnO3

“…Double exchange usually mediates the ferromagnetic state, while superexchange usually mediates an antiferromagnetic state in magnetic oxides. 4,17,29 At the surface of magnetic nanoparticles, there are broken and incomplete chemical bonds that can randomly change the balance of ferromagnetic and antiferromagnetic exchange interactions, thereby providing randomness and frustration for the surface spin glass. In the presence of the 50 mT applied field, which is larger in magnitude than the low temperature coercive field of the sample, the Zeeman energy overcomes the interaction of the spins with their surroundings and the kink disappears.…”

“…[1][2][3][4] In general, the magnetic properties of nanoparticles are strongly influenced by changing their size. The static and dynamic magnetic response of a small single-domain magnetic nanoparticle can be considered equivalent to the response of a single large spin, called a macrospin or superspin.…”

“…5,[9][10][11][12][14][15][16] The La 1-x Sr x MnO 3 perovskite manganites are some of the most captivating magnetic materials due to their colossal magnetoresistance, half-metallicity, and magnetocaloric and optical properties. 4,17,18 Among these manganites, La 1-x Sr x MnO 3 with x ¼ 0.33 has the highest Curie temperature of 380 K. 18 Single-domain magnetic nanoparticles with large saturation magnetization and a Curie temperature above room temperature have potential for use in hyperthermia, MRI contrast enhancement, and drug delivery applications. It is therefore pertinent to study the static and dynamic magnetic properties of the optimally doped manganite.…”

Cooling-field dependence of exchange bias effect in La0.45Sr0.55MnO3 nanoparticles

“…Magnetic properties were studied using a Quantum Design MPMS 5 T SQUID magnetometer and an AC magnetic susceptometer (Lake Shore, model 7000). The magnetization at 5 K first increases with particle size from 1.0 l B / Mn for 16 nm to 1.5 l B /Mn for 36 nm before falling abruptly in larger particles, 21 which have an A-type antiferromagnetic spin structure. 22 We focus on the particles with 2r ¼ 16 nm.…”

Robust antiferromagnetic coupling in hard-soft bi-magnetic core/shell nanoparticles

“…In fact, some of these novel properties have resulted in prospective applications of these materials in diverse fields as magnetic recording (enhanced blocking temperature) 6 , hard magnets (increased energy products) 2 , shielding (superior microwave absorption) 7 , magnetoresistive devices (enhanced magnetoresistance after field cooling) 8 , improved magnetocaloric materials 9 , magnetic resonance amplifiers 10 or in biomedical applications (optimized hyperthermia and magnetic resonance imaging) 11,12 . Importantly, in all these experimental core/shell nanoparticles studies only ferromagnetic (FM) coupling between the counterparts (i.e., the spins of the core and the shell are aligned parallel to each other) has been reported.…”