Strain Induced Nanopillars and Variation of Magnetic Properties in La_(0.825)Sr_(0.175)MnO_3/LaAlO_3 Films

To investigate the process of strain relaxation and resultant variation of microstructure and magnetic properties,low-doped La_(0.825)Sr_(0.175)MnO_3 epitaxial films with different thicknesses are deposited on LaAlO_3 substrates and strain induced nanopillars are discovered inside the La_(0.825) Sr_(0.175)MnO_3 film. Perpendicular oriented nanopillars mainly exist below 30 nm and tend to disappear above 30 nm. The distribution of nanopillars not only induce the variation of lattice parameters and local structural distortion but also lead to the deviation of easy magnetization axis from the perpendicular direction. Specifically, the out-of-plane lattice parameters of the film decrease quickly with the increase of the thickness but tend to be constant when the thickness is above 30 nm. Meanwhile, the variations of magnetic properties along in-plane and out-of-plane directions would also decline at first and they then remain nearly unchanged. Our work constructs the relationship between nanopillars and magnetic properties inside films. We are able to clearly reveal the effects of inhomogeneous strain relaxation.     

Magnetic and Magnetocaloric Properties of Polycrystalline and Oriented Mn_(2-δ)Sn

Mn-based Heusler alloys have attracted significant research attention as half-metallic materials because of their giant magnetocr.ystalline anisotropy and magnetocaloric properties.We investigate the crystal structure and magnetic properties of polycrystalline,[101]-oriented,and[100]-oriented Mn_(2-δ) Sn prepared separately by arc melting,the Bridgeman method,and the flux method.All of these compounds crystallize in a Ni_2 In-type structure.In the Mn_(2-δ)Sn lattice,Mn atoms occupy all of the 2 a and a fraction of the 2 d sites.Site disorder exists between Mn and Sn atoms in the 2 c sites.In addition,these compounds undergo a re-entrant spin-glass-like transition at low temperatures,which is caused by frustration and randomness within the spin system.The magnetic properties of these systems depend on the crystal directions,which means that the magnetic interactions differ significantly along different directions.Furthermore,these materials exhibit a giant magnetocaloric effect near the Curie temperature.The largest value of maximum of magnetic entropy change(-△S_M)occurs perpendicular to the[100]direction.Specifically,at 252 K,maximum-△S_M is 2.91 and 3.64 J-kg~(-1)K~(-1) for a magnetic field of 5 and7 T,respectively.The working temperature span over 80 K and the relative cooling power reaches 302 J/kg for a magnetic field of 7 T,which makes the Mn_(2-δ)Sn compound a promising candidate for a magnetic refrigerator.