Coexistence of ferromagnetic and spin-glass phenomena in La_1-xCa_xMnO₃(0⩽x⩽0.4)

Abstract

Low-field magnetic properties of ceramic La1-xCaxMnO3 (0⩽x⩽0.4) are investigated between T = 5 and 310 K. The paramagnetic-ferromagnetic transition is observed in all the samples. The dependence of the Curie temperature, TC, on x is described within a model of spin polarons associated with electronic localization. Critical behaviour of the susceptibility χ-1(T ) ~ (T-TC)γ is observed for T>TC, with the critical exponents γ = 1.20±0.05 and γ* = 1.64±0.06 below and above the composition x≈0.18 corresponding to the Mn4+ ion concentration c ≈ 0.23, respectively. For the compound with x = 0.3 no temperature hysteresis of the resistivity is observed in magnetic fields between 0 and 8 T. In all the samples the field-cooled and zero-field-cooled magnetizations deviate below TC, the difference being approximately equal to the thermoremanent magnetization (TRM). Long-time relaxation of TRM in LCMO is observed for time scales up to 104 s. The relaxation rate reaches a maximum near a wait time tW ~ 103 s. The time dependence of TRM can be described with a stretched exponential law, as in spin or cluster glasses in conditions where the observation time is comparable with tW .

Large magnetoresistance in (La1−xCaxMnO3)1−y:ZrO2 composite

“…Formation of La 2 Zr 2 O 7 , which starts at yϭ0.10 and becomes prominent as y increases further up to yϭ0.40, shifts the stoichiometry towards the higher Ca side and T C is pushed up towards higher temperatures. The variation of T C with mole % of ZrO 2 ͑y͒ matches qualitatively the variation of T C with Ca content ͑x͒ in LCMO as reported by Laiho et al 13 They have reported T C , which varies from around 175 K for xϭ0.0 to around 260 K for xϭ0.40. However our pure LCMO (yϭ0.0) shows lower T C , which may be due to the presence of nonstoichiometric defects such as oxygen ion excess or La ϩ3 , Ca ϩ2 vacancies etc., which results in an increment of electron scattering centers as proposed by Massa et Temperature variations of resistivity between 5 and 375 K of the composites have been shown in Fig.…”

Phase separation, ferromagnetism and magnetic irreversibility in La1−xSrxMn1−yFeyO3

“…LSMFO samples with x¼0.3 and y¼0.15 (#15), 0.20 (#20) and 0.25 (#25) were synthesized with the conventional solid-state reaction method, similar to preparation of La 1À x Ca x MnO 3 [25], from La 2 O 3 , MnO 2 , Fe 2 O 3 and SrCO 3 . The starting materials were precalcined to remove possible adsorbates, weighted in stoichiometric proportions and mixed with subsequent heating in air at 1360 1C for 40 h and intermediate grindings.…”

“…Another interesting feature of LSMFO is the magnetic irreversibility, pertinent to frustrated systems such as spin-glasses or cluster-glasses [24], and observed together with the FM transition [20]. Coexistence of the FM and glassy properties has been found in many other manganite perovskites like La 1À x Ca x MnO 3 [25], La 1À x Ca x Mn 1À y Fe y O 3 [23], La 1À x Ba x MnO 3 [26], Nd 0.7 Sr 0.3 MnO 3 [27] and Y 0.7 Ca 0.3 MnO 3 [28], although its connection to the phase separation is not understood well enough.…”

Macroscopic behavior and microscopic magnetic properties of nanocarbon

“…We find that B K E1 T in # 1À 3 and it lies between $1 À 5 T in # 4, whereas the temperature dependence of the magnetization acquires an upturn below $ 50 K. Only a small deviation of TRM (T) from the difference of M FC (T) À M ZFC (T), following from Fig. 3, indicates an insignificant non-sphericity of magnetic particles [30,31], which is in agreement with the AFM data [24].…”