Nonlinear susceptibilities as a probe to unambiguously distinguish between canonical and cluster spin glasses

Treating the randomly Fe-substituted optimally hole-doped manganite La0.7Pb0.3(Mn1−yFey)O3 (y=0.2,0.3) as a test case, we demonstrate that a combined investigation of both odd and even harmonics of the ac magnetic response permits an unambiguous distinction between the canonical and cluster spin glasses. As expected for a spin glass (SG), the nonlinear ac magnetic susceptibilities χ3(T,ω) and χ5(T,ω) (odd armonics) diverge at the SG freezing temperature Tg=80.00(3) K [Tg=56.25(5) K] in the static limit and, like the imaginary part of the linear susceptibility, follow dynamic scaling with the critical exponents β=0.56(3) [β=0.63(3)], γ=1.80(5) [γ=2.0(1)], and zν=10.1(1) [zν=8.0(5)] in the sample with composition y=0.2 (y=0.3). The nonlinear susceptibility χNL, which has contributions from both χ3 and χ5, satisfies static scaling with the same choice of Tg, β, and γ. Irrespective of the Fe concentration, the values of the critical exponents γ, ν, and η are in much better agreement with those theoretically predicted for a three-dimensional (d=3) Heisenberg chiral SG than for a d=3 Ising SG. The true thermodynamic nature of the “zero-field” spin-glass transition is preserved even in finite magnetic fields. Unlike odd harmonics, even harmonics χ2(T,ω) and χ4(T,ω) make it evident that, apart from the macroscopic length scale of the spin-glass order in the static limit, there exists a length scale that corresponds to the short-range ferromagnetic order.This work was supported by the Department of Science and Technology, India, through Grant No. IR/S5/IU-01/2006, and by the Spanish Ministry for Education through the grant No. SAB 2010-0091. S.N.K. is thankful to the Department of Science and Technology, India, for financial support through the J. C. Bose National Fellowship. Y.B. thanks the Council for Scientific and Industrial Research, India, for the financial support through a Senior Research Fellowship. The authors thank J. M. Barandiaran and J. Gutiérrez for providing the samples

Observation of isotropic-dipolar to isotropic-Heisenberg crossover in Co-and Ni-substituted manganites

High-precision ac susceptibility data have been taken on the La0.7Pb0.3Mn1?y (Co, Ni)yO3 (y = 0, 0.1, 0.2 and 0.3) manganite system over a wide range of amplitudes and frequencies of the ac driving field in a temperature range that embraces the critical region near the ferromagnetic (FM)?paramagnetic (PM) phase transition (occurring at the Curie point TC). Elaborate data analysis was performed that (i) enabled the first observation of a crossover from a three-dimensional (3D; d = 3) isotropic long-range dipolar asymptotic critical behavior to a d = 3 isotropic short-range Heisenberg critical regime as the temperature is raised from TC in the compositions y 6= 0 (no such crossover is observed in the parent compound, y = 0) and (ii) brought out clearly the importance of dipole?dipole interactions between the eg electron spins and/or between eg?t2g electron spins in establishing long-range FM order in the insulating state. The final charge and spin states of Co and Ni ions, substituting for the Mn3+ and/or Mn4+ ions, are arrived at by using a scenario of substitution that is consistent not only with the present results but also with the previously published structural, thermo-gravimetric, bulk magnetization, dc magnetic susceptibility and electrical resistivity data on the same system. The marked similarity seen between the magnetic behavior of the manganite system in question and the quenched random-exchange ferromagnets, within and outside the critical region, suggests that the percolation model forms an adequate description of the FM metal-to-PM insulator transition

Unravelling the nature of ferromagnetic-paramagnetic phase transition and its bearing on colossal magnetoresistance in nanocrystalline La

The nature of the ferromagnetic (FM)-paramagnetic (PM) phase transition at $T = T_{C}$ changes from first order to second order when the average crystallite size, d, falls below 100 nm in optimally hole-doped nanocrystalline La1−xCaxMnO3. In zero field, the systems with d < 100 behave as a three-dimensional (3D) uniaxial dipolar ferromagnet in the asymptotic critical region but in finite fields, the asymptotic critical behavior changes over to that of a 3D Ising ferromagnet. How effectively polaron correlations couple magnetic degrees of freedom to the lattice decides the order of the FM-PM transition and the magnitude of colossal magnetoresistance (CMR). d alters the electron-lattice coupling and thereby enables the tuning of CMR over an unusually wide temperature range

Development of magnetoelectric nanocomposite for soft technology

The proliferation of flexible and stretchable electronics has led to substantial advancements in principles, material combinations and technologies. The integration of magnetoelectric systems in soft electronics is inevitable by virtue of their extensive applications. Recently, 2D layered materials have emerged as potential candidates due to their excellent flexibility and atomic-scale thickness scalability in addition to their interesting physics. This paper presents a new perspective on the development of magnetoelectric nanocomposites through materials engineering on a pliant mica with excellent mechanical, thermal and chemical stabilities. The unique features of 2D muscovite mica and the power of van der Waals epitaxy are expected to contribute significantly to the emerging transparent soft-technology research applications

Mean-field treatment of nonlinear susceptibilities for a ferromagnet of arbitrary spin

The intrinsic linear and nonlinear magnetic susceptibilities, χn, for a ferromagnet of arbitrary spin, calculated using the mean-field approximation, are shown to diverge in the asymptotic critical region (ACR) with the exponent γn=nγ+(n− 1)β and n=1, 2, … . This behaviour of χn in the ACR is consistent with the scaling equation of state. With increasing spin, the divergence in χn(T), as the ferromagnetic-paramagnetic phase transition temperature, TC, is approached from below or above, progressively slows down with the result that the width of the ACR increases. For a given spin, the higher the order of nonlinear susceptibility, the narrower the ACR. These results are in qualitative agreement with the critical behaviour of χn(T) observed in an archetypal ferromagnet

van der Waals heteroepitaxy on muscovite

As current electronics makes a transition from bulky and rigid templates to lightweight and flexible ones, the emerging field of soft technology is set to revolutionize our daily life. Currently, polymer based templates dominate this field due to their excellent mechanical characteristics and low cost, but limited thermal budget and stabilities are the major technological bottlenecks resulting in poor performance and short duration of lifetime. Recently, the technology based on van der Waals heteroepitaxy on muscovite is considered as a promising solution to overcome these barriers at once. In this paper, the characteristics of muscovite and the mechanism of van der Waals heteroepitaxy will be introduced, after that, a variety of materials on muscovite via van der Waals heteroepitaxy and the efforts on practical applications are reported. With the outlook of material science and help of advanced measurements, the evidence of heteroepitaxy of muscovite and overlayers has been deeply analyzed. Moreover, various measurements of properties was carried under bending conditions to demonstrate the mechanical stability and reliability. Through this review, we pave the path to develop more material systems on muscovite to make MICAtronics completely

Low-Temperature Magnetic and Magnetocaloric Properties of Manganese-Substituted Gd0.5Er0.5CrO3 Orthochromites

Rare-earth chromites have been envisioned to replace gas-based refrigeration technology because of their promising magnetocaloric properties at low temperatures, especially in the liquid helium temperature range. Here, we report the low-temperature magnetic and magnetocaloric properties of Gd0.5Er0.5Cr1&minus;xMnxO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) rare-earth orthochromites. The N&eacute;el transition temperature (TN) was suppressed from 144 K for Gd0.5Er0.5CrO3 to 66 K for the Gd0.5Er0.5Cr0.5Mn0.5O3 compound. Furthermore, magnetization reversal was observed in the magnetization versus temperature behavior of the Gd0.5Er0.5Cr0.6Mn0.4O3 and Gd0.5Er0.5Cr0.5Mn0.5O3 compounds at 100 Oe applied magnetic field. The magnetic entropy change (&minus;&#8710;S) value varied from 16.74 J/kg-K to 7.46 J/kg-K, whereas the relative cooling power (RCP) ranged from 375.94 J/kg to 220.22 J/kg with a Mn ion concentration at 5 T field and around 7.5 K temperature. The experimental results were substantiated by a theoretical model. The present values of the magnetocaloric effect are higher than those of many undoped chromites, manganites and molecular magnets in the liquid helium temperature range

Low-Temperature Magnetic and Magnetocaloric Properties of Manganese-Substituted Gd_0.5Er_0.5CrO₃ Orthochromites

Rare-earth chromites have been envisioned to replace gas-based refrigeration technology because of their promising magnetocaloric properties at low temperatures, especially in the liquid helium temperature range. Here, we report the low-temperature magnetic and magnetocaloric properties of Gd0.5Er0.5Cr1−xMnxO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) rare-earth orthochromites. The Néel transition temperature (TN) was suppressed from 144 K for Gd0.5Er0.5CrO3 to 66 K for the Gd0.5Er0.5Cr0.5Mn0.5O3 compound. Furthermore, magnetization reversal was observed in the magnetization versus temperature behavior of the Gd0.5Er0.5Cr0.6Mn0.4O3 and Gd0.5Er0.5Cr0.5Mn0.5O3 compounds at 100 Oe applied magnetic field. The magnetic entropy change (−∆S) value varied from 16.74 J/kg-K to 7.46 J/kg-K, whereas the relative cooling power (RCP) ranged from 375.94 J/kg to 220.22 J/kg with a Mn ion concentration at 5 T field and around 7.5 K temperature. The experimental results were substantiated by a theoretical model. The present values of the magnetocaloric effect are higher than those of many undoped chromites, manganites and molecular magnets in the liquid helium temperature range

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices

Self-assembling epitaxial growth of a single crystalline CoFe2O4 nanopillar array via dual-target pulsed laser deposition

Magnetic nanopillars are promising for a variety of technological applications, though the template-free fabrication of magnetic nanopillar arrays with good crystallinity and uniform distribution remains a substantial challenge. Herein, we report successful fabrication of a regular array of CoFe2O4 (CFO) nanopillars using an elaborately designed dual-target pulsed laser deposition (PLD) process, which exhibit a truncated pyramid surface with consistent size and orientation as well as uniform distribution. Detailed X-ray diffraction, scanning transmission electron microscopy and X-ray photoelectron spectroscopy demonstrate the high quality nature of the CFO nanopillars, while vibrating sample magnetometer and magnetic force microscopy studies confirm their room temperature magnetism. This dual-target PLD process takes advantage of BiFeO3 decomposition, and the subsequent formation of CFO nanopillars requires no template, giving us a powerful technique to prepare oxide nanopillars with desired composition and functional properties