Linear and nonlinear ac susceptibilities in polycrystalline low-bandwidth Pr_1−xCa_xMnO₃(x= 0.0 − 0.3) manganite

Abstract

The complex linear and nonlinear ac susceptibility have been thoroughly investigated in the low bandwidth manganite compound Pr(1-x)Ca(x)MnO3 (PCMO) for the doping range x = 0.0-0.3 with and without a superimposed background dc field. The dynamical ac response shows substantial differences between the samples. The sample with x = 0.1 is found to have two separate magnetic transition peaks, compared to the single transitions in the samples x = 0.0 and x = 0.2. The nonlinear ac susceptibility measurements were compared between samples, which confirmed that these transition peaks are similar in nature and from the same magnetic origin. Additionally, for sample x = 0.3 a complex transition peak structure with overlapping transition peaks was found. This kind of evolution of the magnetic phases as a function of the Ca concentration is believed to rise from coexisting antiferromagnetic (AFM) and ferromagnetic (FM) orderings, where the Ca concentration controls the amount of FM clusters in the sample. The spin glass characteristics of these complex phase-separated magnetic regimes showed similarities and contradictions with conventional spin glasses, which indicates that this cluster glass behavior arises from the frustration between competing AFM and FM clusters having different magnetic exchange interaction.

Nonpercolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime ofLa1−xCaxMnO3

“…By taking this into account in the current analysis we obtain a rather different view of the evolution of the metallic and insulating phase fractions with temperature and doping in La 1−x Ca x MnO 3 . The behavior is different from cubic manganite systems with smaller A-site ions such as Pr 1−x Ca x MnO 3 55,56 where phase coexistence has been clearly established on a longer length-scale. On the other hand, the behavior of La 1−x Ca x MnO 3 and La 1−x Sr x MnO 3 systems are likely to be similar to each other, despite the suggestion of a percolative transition in that system from early PDF data 44 .…”

Control of Surface Segregation in Bimetallic NiCr Nanoalloys Immersed in Ag Matrix

“…Interestingly, the FC curve of the Ni 95 Cr 5 :Ag nanocomposite shows almost the temperature independent behavior below T B ; thus, Cr-segregation was effectively prevented due to protection by the Ag matrix. The field-dependent ZFC peak ( T B ) and near-constant FC magnetization curves below T B indicate spin-glass type features161718, possibly due to a slight surface-spin disorder caused by interfacial interaction with the Ag matrix. Thus, Ni 95 Cr 5 nanograins behave more like a core-shell spin-structure with an ordered, ferromagnetic Ni 95 Cr 5 core, represented by T B , surrounded by a spin-disordered shell.…”

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

“…From the fitting shown in the inset of Fig. 7(b), the obtained values of parameter n range between 0.07 and 0.37, revealing cluster-glass rather than canonical spin-glass behavior: n < 2/3 is the fingerprint of cluster-glass formation, whereas for the so-called de Almeida-Thouless line, characteristic of spin glasses, n = 2/3 [52,55]. [56].…”

“…Moreover, the irreversibility in the present case occurs in closer vicinity of T S (T irr ≈ T S ) with increasing Cr content, unlike in ideal superparamagnetic systems [51], where it is expected to start well above T S (T irr > T S ). This behavior normally indicates cluster glass features of concentrated magnetic systems and magnetic disorder [51,52], or a superparamagnetic material with dipolar interactions [51,52]. Thus, the samples may have complex magnetic phases with coexisting anti-FM-FM ordering, where the anti-FM (due to the Cr segregates) and FM (due to Ni-rich particle cores) clusters are competing.…”