Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into La4/3Sr5/3Mn2O7 ,from the resulting single crystal (La0.8Eu0.2)4/3Sr5/3Mn2O7 we have observed the magnetization jump,the resistivity jump,as well as the relaxation phenomena. For (La0.8Eu0.2)4/3Sr5/3Mn2O7 ,it has a very delicate ground state due to the interplays among spin,charge,orbital,lattice degrees of freedom. Consequently,the magnetization state is sensitive to temperature,magnetic field,as well as time. Meanwhile,the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of La4/3Sr5/3Mn2O7 and cause such interesting behaviours.
We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd0.5Sr0.5xBaxMnO3 (x=0.1). Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K (～TC ) and 185 K (～TN ),the system coexists of the paramagnetic phase and the ferromagnetic (FM) phase. Between 185 K and 140 K,the system coexists of the FM phase and the antiferromagnetic (AFM) phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba2+ ions for the smaller Sr2+ ions.
Large low-field-induced magnetic entropy changes, ΔSM, are observed in La0.67Ca0.33MnO3 and La0.67-Ca0.33Mn0.96Fe0.04O3 single crystals. The peaks of ΔSM broadened asymmetrically to high temperatures under higher magnetic fields for two materials should be attributed to the first-order magnetic phase transition at Tc. A small amount of iron doping results in an increase in the refrigerant capacity of the material though the magnetic entropy change decreases. The discovery of excellent magnetocaloric features of these single crystals in the low magnetic field can provide some ideas for exploring novel magnetic refrigerants operating under permanent magnet rather than superconducting one as magnetic field source.
LI GuoKe, ZHANG XiangQun, KOU ZhiQi, LI QingAn, SUN Young & CHENG ZhaoHua State Key Laboratory of Magnetism, Beijing National Laboratory of Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
