Vortex dynamics and irreversibility line in optimally doped SmFeAsO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:mn>8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>F<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>from ac suscept

We discuss the magnetic properties of a Sm2Mo2O7 single crystal as investigated by means of different experimental techniques. In the literature, a conventional itinerant ferromagnetic state is reported for the Mo 4+ sublattice below ∼ 78 K. However, our results of dc magnetometry, muon spin spectroscopy (µ + SR) and high-harmonics magnetic ac susceptibility unambiguously evidence highly disordered conditions in this phase, in spite of the crystalline and chemical order. This disordered magnetic state shares several common features with amorphous ferromagnetic alloys. This scenario for Sm2Mo2O7 is supported by the anomalously high values of the critical exponents, as mainly deduced by a scaling analysis of our dc magnetization data and confirmed by the other techniques. Moreover, µ + SR detects a significant static magnetic disorder at the microscopic scale. At the same time, the critical divergence of the third-harmonic component of the ac magnetic susceptibility around ∼ 78 K leads to additional evidence towards the glassy nature of this magnetic phase. Finally, the longitudinal relaxation of µ + spin polarization (also supported by results of ac susceptibility) evidences re-entrant glassy features similar to amorphous ferromagnets.

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“…[126][127][128] However, in the current case of Sm 2 Mo 2 O 7 no choice of T AT (0) helps to recover a De Almeida -Thouless behaviour.…”

Section: Amfamentioning

confidence: 99%

Amorphous ferromagnetism and re-entrant magnetic glassiness in single-crystallineSm2Mo2O7

et al. 2014

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“…7 shows a crossover occurring in τ c , during the slowing-down of the FLL motion, upon cooling. Hence the Arrhenius law, typically employed in cuprates [23] and in the SmFeAsO 0.8 F 0.2 [24], fails in this system. One can further realize that the Arrhenius law has to be abandoned, by plotting ν versus the temperature of the peak, as recently done in the optimally doped Ba(Fe 1−x Co x ) 2 As 2 [22].…”

mentioning

confidence: 94%

Glassy transition in the vortex lattice of Ba(Fe _0.93 Rh _0.07 ) ₂ As ₂ superconductor probed by NMR and ac-susceptibility

Bossoni¹,

Carretta²,

Horvatić³

et al. 2013

EPL

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-By using Nuclear Magnetic Resonance and ac-susceptibility, the characteristic correlation times for the vortex dynamics, in an iron-based superconductor, have been derived. Upon cooling, the vortex dynamics displays a crossover consistent with a vortex glass transition. The correlation times, in the fast motions regime, merge onto a universal curve which is fit by the Vogel-Fulcher law, rather than by an Arrhenius law. Moreover, the pinning barrier shows a weak dependence on the magnetic field which can be heuristically justified within a fragile glass scenario. In addition, the glass freezing temperatures obtained by the two techniques merge onto the de Almeida-Thouless line. Finally the phase diagram for the mixed phase has been derived.Introduction. -The discovery of iron-based superconductors has brought to a renewed interest in the study of the mixed phase of type-II superconductors and of the nature of the frozen vortex state. In this regard, the effect of quenched disorder on the flux lines lattice (FLL) properties has to be considered, together with the onset of a vortex glassy state [1][2][3][4]. In the case of weakly anisotropic superconductors, such as the 122 family of iron-pnictides, the high temperature (T ) region of the phase diagram is dominated, just below the transition temperature T c , by a high mobility state of vortex lines [5]. On the other hand, the nature of the low temperature vortex lattice (VL) dynamics is still debated, since it involves the complex interplay among the pinning forces, the intervortex repulsion/attraction [6] and the thermal excitations. In a recent theoretical work [7] the free energy of the vortex matter was explicitly calculated for a three dimensional (3D) superconductor, in presence of quenched disorder. Two transitions were found: a first-order melting, at which the quasi-long-range order is destroyed, and a second-order glassy transition. Such double transition has been recently experimentally observed in cuprates [8]. By taking advantage of the work carried out in cuprates,

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“…The observation of H irr (T ) values lying well below the H c2 (T ) values over the entire H-T vortex phase diagram has been a distinct feature seen in a wide variety of low-T c and high-T c superconductors [33][34][35][36][37][38][39]. Here it is worthwhile to look at its ramifications on the exponents within the Dew-Hughes scenario for the iron chalcogenide superconductor under consideration.…”

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Magnetization hysteresis and time decay measurements in FeSe0.50Te0.50: Evidence for fluctuation in mean free path induced pinning

et al. 2011

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We present results of magnetic measurements relating to vortex phase diagram in a single crystal of FeSe 0.5 Te 0.5 which displays second magnetization peak anomaly for H c. The possible role of the crystalline anisotropy on vortex pinning is explored via magnetic torque magnetometry. We present evidence in favor of pinning related to spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for both H c and H ⊥ c. This is further corroborated using magnetization data for H c in a single crystal of FeSe 0.35 Te 0.65 . Dynamical response across second magnetization peak (SMP) anomaly in FeSe 0.5 Te 0.5 has been compared with that across the well researched phenomenon of peak effect (PE) in a single crystal of CeRu 2 .

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Vortex dynamics and irreversibility line in optimally doped SmFeAsO0.8F0.2from ac suscept

Cited by 52 publications

References 48 publications

Amorphous ferromagnetism and re-entrant magnetic glassiness in single-crystallineSm2Mo2O7

Amorphous ferromagnetism and re-entrant magnetic glassiness in single-crystallineSm2Mo2O7

Glassy transition in the vortex lattice of Ba(Fe _0.93 Rh _0.07 ) ₂ As ₂ superconductor probed by NMR and ac-susceptibility

Magnetization hysteresis and time decay measurements in FeSe0.50Te0.50: Evidence for fluctuation in mean free path induced pinning

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Vortex dynamics and irreversibility line in optimally doped SmFeAsO0.8F0.2from ac suscept

Cited by 52 publications

References 48 publications

Amorphous ferromagnetism and re-entrant magnetic glassiness in single-crystallineSm2Mo2O7

Amorphous ferromagnetism and re-entrant magnetic glassiness in single-crystallineSm2Mo2O7

Glassy transition in the vortex lattice of Ba(Fe 0.93 Rh 0.07 ) 2 As 2 superconductor probed by NMR and ac-susceptibility

Magnetization hysteresis and time decay measurements in FeSe0.50Te0.50: Evidence for fluctuation in mean free path induced pinning

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Glassy transition in the vortex lattice of Ba(Fe _0.93 Rh _0.07 ) ₂ As ₂ superconductor probed by NMR and ac-susceptibility