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Observation of a Griffiths-like phase in bilayered manganites
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The authors report the observation of a Griffiths-like phase in La2−2xSr1+2xMn2O7 (x = 0.30, 0.33, and 0.40) and (La0.8Eu0.2)2−2xSr1+2xMn2O7 (x = 0.33) single crystals by means of electron spin resonance, magnetic susceptibility, and magnetoresistance measurements. In the temperature region TC<T<350 K, the resonance signal consists of a ferromagnetic resonance line and a paramagnetic resonance line, which suggests that the system is not in a pure paramagnetic phase. The ferromagnetic resonance signal disappears and the magnetic susceptibility starts to deviate from the Curie-Weiss law at the same temperature T* ≈ 350 K, independent of doping level and anisotropy. These results indicate that a Griffiths-like phase exists at TC<T<T* in bilayered manganites, which is due to intrinsic inhomogeneity caused by quenched disorder.
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... In addition to this, the understanding of Griffith phase in the paramagnetic region is an interesting issue in manganites. However, ESR studies confirm the presence of Griffith Phase [11] in the paramagnetic region upto higher temperature than the Curie transition temperature in manganites [1,5,[12][13][14][15][16][17][18][19][20][21][22] and in particular LCMO [1,8,14,17]. The quenched disordered structure and clusters of magnetic domains on sample surface is the origin of enhanced Griffith phase to higher temperature [11,16]. ...
... However, ESR studies confirm the presence of Griffith Phase [11] in the paramagnetic region upto higher temperature than the Curie transition temperature in manganites [1,5,[12][13][14][15][16][17][18][19][20][21][22] and in particular LCMO [1,8,14,17]. The quenched disordered structure and clusters of magnetic domains on sample surface is the origin of enhanced Griffith phase to higher temperature [11,16]. It is reported that Griffith phase is observed within a temperature range of 20-30 K higher than the paramagnetic to ferromagnetic transition temperature. ...
... Contents lists available at ScienceDirect [16]. The higher value of transition temperature is also depending upon the content of oxygen and the oxygen deficiency helps in increasing the transition temperature [14]. ...
We report on the possible observation of Griffith phase in a wide range of temperature (> 272 K to 378 K) in the 2.5 minutes plasma sintered La0.67Ca0.33MnO3 (LCMO) as deduced from careful electron spin resonance studies. This is 106 K higher than the paramagnetic to ferromagnetic transition (Curie transition ∼ 272 K) temperature. The indication of Griffith phase in such a wide range is not reported earlier by any group. We purposefully prepared LCMO samples by plasma sintering technique so as to create a disordered structure by rapid quenching which we believe, is the prime reason for the observation of Griffith Phase above the Curie transition temperature. The inverse susceptibility curve represents the existence of ferromagnetic cluster in paramagnetic region. The large resonance peak width (40 mT ∼60 mT) within the temperature range 330 K to 378 K confirms the sample inhomogeneity which is also established from our electron probe microstructure analysis (EPMA). EPMA establishes the presence of higher percentage of Mn³⁺ cluster in comparison to Mn⁴⁺. This is the reason for which Griffith state is enhanced largely to a higher range of temperature.
... The temperature range between T G and T C is termed as the GP region. Although the GP was originally proposed for the Ising ferromagnets, it has been recently suggested for the antiferromagnetic (AFM) systems [20,21], frustrated AFM [23,24], disorder magnet [25], re-entrant cluster glass [26], charge spin glass [27], and manganites [28][29][30]. ...
... The experimental findings using the various macroscopic and microscopic experimental tools already confirmed a shortrange ordered state above T N for both NSO [34,35,37] and MSO [38,40,41,43]. Although proper classification between the short-range ordered state and GP is less understood [64,65], the GP has been proposed in various systems, where the disorder and magnetic frustration were suggested as the key factors for the GP [20,21,[23][24][25][26][27][28][29][30]. In fact, the plenty of reports are available, proposing occurrence of the GP in the spin-glasses or spin-glass like systems [26,27,66], where both the disorder and frustration are the key for the spin-glass states. ...
The compounds, NiSb2O6(NSO) and MnSb2O6(MSO) attract the community for the quasi one-dimensional and layered structure composed of Ni2+and Mn2+, which orders antiferromagnetically at TN= 6.7 and 12 K, respectively. Here, we report the Griffiths-like phase much above TNin the range of 37 - 85 K and 25 - 80 K for NSO and MSO, respectively. The dc magnetization results indicate the Griffiths-like phase, following the modified Curie-Weiss law. The magneto-capacitive responses for both the compounds show anomalies at the onset of the Griffiths-like phase. Intriguingly, the low temperature synchrotron diffraction results are conclusive for determining the singularities for both the compounds. Interplay between the low-dimensionality, magnetic frustration, and magneto-elastic coupling correlates the observed short range ordered state, which is suggested as a Griffiths-like phase, above TNfor both the compounds.
... This well-accepted phenomenon was originally proposed theoretically by Griffiths while describing randomly diluted Ising ferromagnets whose lattice sites are partially occupied with spins and the remaining portions are either filled with nonmagnetic ions or vacant [9]. Experimentally, the GP behavior is observed to appear in diverse systems, e.g., transition-metal oxides (electron-/hole-doped manganites [1,2,5,[10][11][12][13], layered manganites [14], doped cobaltite [15] etc.), double perovskite compounds [16][17][18], intermetallic systems [4,7,19], heavy Fermi materials [3], etc., and, in addition, a Griffiths-like phase can also emerge in other physical scenarios, such as in brain criticality [20] and in the Mott transition (electronic GP) systems [21,22]. The singularities would grow in the temperature regime T C < T < T G , where T C is magnetic transition temperature and the new temperature scale, T G , has been coined as the Griffiths temperature. ...
In this paper, a detailed comprehensive magnetic study on the origin of the Griffiths phase (GP) in the nanocrystalline
La
0.4
(
Ca
0.5
Sr
0.5
)
0.6
MnO
3
compound has been presented. The system exhibits a ferromagnetic (FM)-like transition around
T
C
∼
274 K. Interestingly, above
T
C
, the state is not pure paramagnetic, but a short-range FM interaction or GP is observed and the interaction persists up to the Griffiths transition temperature,
T
G
∼
350 K. The detailed investigation of isothermal magnetization and the magnetocaloric effect along with its theoretical analysis have been employed besides the conventional magnetic measurements to probe the GP. Disorder in the system is introduced via increasing an A-site cationic size mismatch along with an additional defect originated owing to the particle size reduction. The disorder-induced magnetic phase transition has also been analyzed by critical analysis. A correlation between the unusual critical parameters with the GP has been furnished.
... Consequently, a competition between FM and AFM will be produced since a gradually enhanced FM state, in which the short-range FM clusters and competing magnetic disorder are also formed and thus should be associated with the observed SG and GP in the system. 22 In order to explore the GP in Ge 1−x Sn x NFe 3 , we perform the χ −1 (T) for all series of samples under ZFC process with H = 100 Oe as shown in Figure 5C. A well CW fitting in higher concentration region can be obtained; for low Sn concentration (x < 0.5), the obvious downward phenomenon deviating gradually from CW behavior is observed, which is known as the typical signature of GP and was also observed in other various systems. ...
We report the Griffiths phase (GP) and transport behavior in the quaternary antiperovskite nitrides Ge1−xSnxNFe3 by a series of systematical magnetic susceptibility and thermoelectric behavior measurements. All the corresponding fitting exponent parameters λGP = 0.852 and 0.854 completely satisfy 0 ≤ λ ≤ 1 in GP regions for Ge0.7Sn0.3NFe3 and Ge0.8Sn0.2NFe3, respectively, indicating the different ferromagnetic concentrations in the system. An observed structural transition from distorted tetragonal structure (I4/mcm) to cubic antiperovskite (Pm3m) with increasing dopants should be responsible for the GP in Ge1−xSnxNFe3, which results in a magnetic phase transition from ferromagnetism (FM) to antiferromagnetism (AFM). Furthermore, the studies of electrical transport properties indicate that the Ge1−xSnxNFe3 series of compounds perform a Fermi liquid behavior at low temperature while the stronger electron‐phonon scatterings are found in the high‐temperature region. In addition, the intensive electron–electron correlation is also determined since much higher value of lattice thermal conductivity κl than the one of electronic thermal conductivity κe.
Double perovskites Dy2CoMnO6 (DCMO) was synthesized by a sol-gel method and the structure and magnetic properties were systematically investigated. Both X-ray diffraction and Raman spectrum indicate that double pervoskite DCMO has a monoclinic structure with a space group P21/n. A Griffiths phase is confirmed to be existing in DCMO by the magnetic behaviors, which is significantly different from the behaviors of the non-Griffiths phase of Gd2CoMnO6 (GCMO) recently reported in reference. It is suggested that the origins of the different short-range magnetic orders of them can be attributed to the different 3d-4f exchange interactions in DCMO and GCMO, besides the effect of the unavoidable anti-site disorder, interrupting the long-range ferromagnetic (FM) order of Co²⁺-O-Mn⁴⁺, resulting in the formation of short-range FM order. The effects of A-site rare-earth Re³⁺ ions on the magnetism of double perovskite Re2Co(Ni)MnO6 are dominated by the combining and competing functions of the radius and the moments of rare earth ions (or the 3d-4f exchange interactions). The FM/AFM coupling is not only related to the most outer 4 f electrons of the rare earth ions, but also to the inner 5d/6 s orbital electrons.
We report the synthesis and magnetic properties of ternary iron nitride compounds Sn1−xNFe3+x (0≤x≤0.4). The magnetic frustration state is found in SnNFe3, and the antiferromagnetic (AFM) exchange is dominant in Sn0.95NFe3.05 and Sn0.9NFe3.1, and then the ferromagnetic (FM) interaction occurs in Sn1−xNFe3+x (0.2≤x≤0.4). Interestingly, the Griffiths phase is observed in x=0.1, 0.2, caused by the FM coupling competing over the AFM one and forming the short-range FM cluster. At the same time, the competitions between the AFM and FM interactions lead to a spin-glass behavior, which is embodied most evidently in Sn0.7NFe3.3 and further confirmed by the corresponding characteristic fitting parameters (τ0=8.89×10−12s, T0=25K, and zv=6.56). In addition, density functional theory (DFT) calculations exhibit the magnetic ground states, magnetic moments contribution, and bonds nature of Sn-Fe and N-Fe. The results of DFT calculations disclose some detailed magnetic interactions, which are demonstrated to be an evidential response to the interesting magnetic behavior in Sn1−xNFe3+x compounds.
In this work we report detailed experimental results and band structure calculations to establish a subtle link between the crystal structure and Griffiths phase (GP) behavior for the geometrically frustrated intermetallic GdMxSn2−δ (M = Co, Ni, Cu; 0<x<1,0≤δ≤0.22) compounds. The crystal structure analysis through powder x-ray diffraction patterns reveals that the atomic positions of the M atoms in the GP analogs are slightly displaced in comparison to those of non-GP members of this series. Further, the band structure calculation shows that this slightly differing atomic position of M atoms results in narrowing in M d bands and the ferromagnetic clusters centered on the T atoms are responsible for GP behavior. This effect is insignificant in non-GP members.
Samples of (La0.8Eu0.2)4/3Sr5/3Mn2O7 were prepared by solid state reaction method. X-ray diffraction patterns indicated that the sample shows no any asymmetry and no any trace of secondary phase. The magnetization curve as a function of temperature (M-T), the magnetization versus magnetic field (M-H) at different temperatures, and the electron spin resonance spectrum have been detected. The magnetization measurement reveals that with lowing temperature, all of the samples undergo a complex magnetic transition. They transform from the two-dimensional short-range ferromagnetic order at TC2D≈282 K, and enter the three-dimensional long-range ferromagnetic state at TC3D≈259 K. Then they step into the antiferromagnetic state at TN≈208 K and enter electric charge temperature order at TCO≈35 K. The antimagnetic phase is found in the sample (La0.8Eu0.2)4/3Sr5/3Mn2O7 below TN. When TC3D = 370 K, the paramagnetic phase and antimagnetic phase co-exist. When TC3D is above 370 K, only paramagnetic phase exists in the sample. Besides, through electrical resistivity versus temperature curve ρ-T, the sample shows the maximum magnetization electrical resistivity when metal-insulator transition temperature is reached TP≈80 K, TP being far from TC3D. And the transition shows the phenomenon of intrinsic magnetization electrical resistance, MR≈61%. The resistance begins to increase below TCO. Because of the lowing temperature, the itinerant electron eg becomes increasingly spontaneously localized. One can see from the fitted ρ-T curves that (La0.8Eu0.2)4/3Sr5/3Mn2O7 in high temperature range is in accordance with the small polaron mode range hopping conduction.
We present the observation of a high-temperature magnetic transition along with ferromagnetic short-range correlations (FSCs) in La2FeMnO6 perovskite system. XPS analysis confirmed the presence of Fe+3 and Mn+3 cations. The M-T curves show two distinct transitions at TC1~60 K and TC~425 K. Coercivity values of ~1140 Oe, and ~35 Oe are observed at 2 K and 300 K respectively. The thermomagnetic analysis reveals the presence of FSCs in La2FeMnO6up to T*= 570 K, well above the transition point, similar to Griffiths-like phase (GP). The presence of ferromagnetic clusters in the paramagnetic region might be due to the intrinsic inhomogeneities associated with the structure, quenched disorder related to the B-site cations and the antisite boundaries. The coefficient of lower temperature electronic specific heat is as high as 59.5 mJmol-1K-2. The electron spin resonance spectra show
ferromagnetic resonance signals that are pointing to the possibility of the presence of FSCs at room temperature. The material seems to be a quite promising candidate for some room temperature applications due to the possibility of coexistence of functionalities like ferromagnetism, ferrimagnetism, GP, magnetotransport coupling, etc. in a single material.
Mixed-valence manganese oxides (R1-x Ax)MnO3 (R=rare-earth cation, A=alkali or alkaline earth cation), with a structure similar to that of perovskite CaTiO3, exhibit a rich variety of crystallographic, electronic and magnetic phases. Historically they led to the formulation of new physical concepts such as double exchange and the Jahn-Teller polaron. More recent work on thin films has revealed new phenomena, including colossal magnetoresistance near the Curie temperature, dense granular magnetoresistance and optically-induced magnetic phase transitions. This review gives an account of the literature on mixed-valence manganites, placing new results in the context of established knowledge of these materials, and other magnetic semiconductors. Issues addressed include the nature of the electronic ground states, the metal-insulator transition as a function of temperature, pressure and applied magnetic field, the electronic transport mechanisms, dielectric and magnetic polaron formation, magnetic localization, the role of cation disorder and the Jahn-Teller effect. Sample preparation, and the properties of related ferromagnetic oxides are also discussed.
We present a systematic electron-spin-resonance (ESR) study in single crystals of La1-xSrxMnO3(0 less than or equal to x less than or equal to 0.2). The temperature dependence of the ESR linewidth marks all significant transitions between both orthorhombic (O',O) and the rhombohedral (R) structural phases of the T-x phase diagram. All significant peculiarities of the ESR spectra for low x values within the O' phase can be attributed to the cooperative Jahn-Teller effect on the Mn3+ e(g) states and to the influence of the Dzyaloshinsky-Moriya exchange interaction. Possible relaxation mechanisms at higher doping levels are discussed.
The fundamental physical properties of doped LaMnO3, generically termed ``manganites,'' and much of the underlying physics, were known more than 40 years ago. This article first reviews progress made at that time, the concept of double exchange in particular, and points out the missing elements that have led to a massive resurgence of interest in these and related materials. More recent research is then described, treating first the ground states that emerge as divalent atoms are substituted for trivalent La. A wide range of ground states appear, including ferromagnetic metals, orbital- and charge-ordered antiferromagnets, and more complex stripe and spin-glass states. Because of the interest in so-called colossal magnetoresistance that occurs in the ferromagnetic/metallic composition range, a section is devoted to reviewing the atypical properties of that phase. Next the high-temperature phase is examined, in particular, evidence for the formation of self-trapped small polarons and the importance of Jahn-Teller coupling in this process. The transitions between the high-temperature polaronic phase and the ferromagnetic and charge-ordered states are treated in a fourth section. In each section, the authors stress the competition among charge, spin, and lattice coupling and review the current state of theoretical understanding. They conclude with some comments on the impact that research on these materials has on our understanding of doped oxides and other strongly correlated electronic materials.
The influence of quenched disorder on the competition between ordered states separated by a first-order transition is investigated. A phase diagram with features resembling quantum-critical behavior is observed, even using classical models. The low-temperature paramagnetic regime consists of coexisting ordered clusters, with randomly oriented order parameters. Extended to manganites, this state is argued to have a colossal magnetoresistance effect. A scale T* for cluster formation is discussed. This is the analog of the Griffiths temperature, but for the case of two competing orders, producing a strong susceptibility to external fields. Cuprates may have similar features, compatible with the large proximity effect of the very underdoped regime.
Recent computational studies of models for manganese oxides have revealed a rich phase diagram, which was not anticipated
in early calculations in this context performed in the 1950s and 1960s. In particular, the transition between the antiferromagnetic
insulator state of the hole-undoped limit and the ferromagnetic metal at finite hole density was found to occur through a
mixed-phase process. When extended Coulomb interactions are included, a microscopically charged inhomogeneous state should
be stabilized. These phase separation tendencies, also present at low electronic densities, influence the properties of the
ferromagnetic region by increasing charge fluctuations. Experimental data reviewed here by applying several techniques for
manganites and other materials are consistent with this scenario. Similarities with results previously discussed in the context
of cuprates are clear from this analysis, although the phase segregation tendencies in manganites appear stronger.
We report the observation of current-induced abrupt transition from a metallic to an insulating state in a bilayered manganite La1.2Sr1.8Mn2O7 single crystal. A colossal electroresistance effect [rho(50mA)-rho(1mA)]/rho(50mA)=93% is found at 120K . Moreover, the current-induced transition is very sensitive to external magnetic fields. At the measuring current of 50mA a low-field colossal magnetoresistance effect, [rho(H)-rho(0)]/rho(0)=-86% , occurs at H=500Oe . This low-field magnetoresistance effect can be repeatedly modulated by external magnetic field. We interpret these phenomena as the consequence of the percolative conduction and local Joule thermal effect.
We present electron spin resonance measurements on single crystals of La1.2Sr1.8Mn2O7. A well-resolved multiline spectrum is observed. There is one paramagnetic resonance line for temperatures above the ordering temperatures. The other lines turn out to arise from a small (< 0.1%) volume fraction of intergrowths.
La1.35Sr1.65Mn2O7 is investigated in the regime where 3D magnetic order is lost but 2D correlations are strong. ESR shows that the localized t2g spins are coupled into intralayer ferromagnetic clusters of fixed size. The eg carriers form polarons with an effective spin growing from 1/2 to 7. ESR and transport properties suggest that the 3D order originates from the onset of coherence of the ferromagnetic clusters mediated by the propagation of the polarons.
At room temperature a large magnetoresistance, DeltaR/R(H=0), of 60% has been observed in thin magnetic films of perovskitelike La-Ba-Mn-O. The films were grown epitaxially on SrTiO3 substrates by off-axis laser deposition. In the as-deposited state, the Curie temperature and the saturation magnetization were considerably lower compared to bulk samples, but were increased by a subsequent heat treatment. The samples show a drop in the resistivity at the magnetic transition, and the existence of magnetic polarons seems to dominate the electric transport in this region.