Magnetic transitions and ferromagnetic clusters inRuSr2(Eu,Ce)

Abstract

The macroscopic magnetizations of a RuSr 2 (Eu 0.7 Ce 0.3 ) 2 Cu 2 O 10ϩ␦ sample were investigated. A ferromagnetlike transition occurs around T M in the low-field magnetization. Highly nonlinear M (H), non-Curie-Weiss susceptibility, and slow spin dynamics, however, were observed up to T 1 Ϸ(2 -3)T M . In addition, an antiferromagnetlike differential-susceptibility maximum of Ru appears around a separate temperature T AM between T 1 and T M . The data are therefore consistent with a phase-separation model: superparamagnetic clusters ͑or short-range spin orders͒ are first precipitated from the paramagnetic matrix below T 1 , followed by an antiferromagnetic transition of the matrix at T AM and an apparent ferromagnetic ͑FM͒ transition around T M , where the long-range spin order is established in the FM species embedded in the matrix.

Study of spin glass and cluster ferromagnetism in RuSr2Eu1.4Ce0.6Cu2O10-δ magneto superconductor

“…The Vogel-Fulcher law fits with the experimental data of the EuRu-1222 well (see Figure 6). Figure 6 shows a linear fit between the freezing temperature 12 Hz from literature for the same system [16,27]. Further same characteristic frequency fitted our data reasonably well (Fig.6).…”

“…The physics of spin glass raises many fundamental questions and has become one of the main streams of research particularly in condensed matter physics. A frequency and field dependent sharp cusp is observed in AC susceptibility around 100 K, indicating metastable magnetism in these systems [12,15,16]. These experimental features are typically found in spinglass (SG), cluster-glass (CG) or superparamagnets (SPM) and even in inhomogeneous ferromagnets etc.…”

“…This is the so [9] and RuSr 2 RECu 2 O 8 for RE = Dy, Ho, Er [10,11]. A phase separation into ferromagnetic (FM) clusters and paramagnetic (PM) matrix followed by an antiferromagnetic (AFM) transition has been assumed to establish magnetic correlations in these systems [12]. Neutron diffraction data [13] did not show unique long range magnetic order, which is encountered more recently [14], primarily in Ru-1222 phase.…”

“…Also, interacting magnetic clusters in the Ru-O 2 planes with no long-range magnetic order, was proposed recently in Nb 1-x Ru x -1222 system [15]. The slow spin dynamics suggested that the FM clusters in Ru-1222 could exhibit superparamagnetism (SPM) [12]. An interesting observation of the frequency dependent peak shift of the AC susceptibility as a function of temperature with thermoremanent magnetization (TRM) measurements [16] revealed spin-glass (SG) behavior in Ru1222, which in a way contradicted the existence of long range magnetic order in these systems.…”

“…Thus, a more careful investigation of the EuRu-1222 system is required to probe the existence of these two metastable states. The existence of the glassy state in the vicinity of the FM transition gives rise to two possible types of SG behavior: reentrant-spin-glass (RSG) [17] or cluster-glass (CG) [12]. …”