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Rinaldi-Montes N, Gorria P, Martínez-Blanco D, Fuertes AB, Barquín LF, Puente-Orench I, Blanco JA. Scrutinizing the role of size reduction on the exchange bias and dynamic magnetic behavior in NiO nanoparticles. NANOTECHNOLOGY 2015; 26:305705. [PMID: 26159463 DOI: 10.1088/0957-4484/26/30/305705] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
NiO nanoparticles (NPs) with a nominal size range of 2-10 nm, synthesized via high-temperature pyrolysis of a nickel nitrate, have been extensively investigated using neutron diffraction and magnetic (ac and dc) measurements. The magnetic behavior of the NPs changes noticeably when their diameter decreases below 4 nm. For NPs larger than or equal to this size, Rietveld analysis of the room temperature neutron diffraction patterns reveals that there is a reduction in the expected magnetic moment per [Formula: see text] ion with respect to bulk NiO, which is linked to the existence of a magnetically disordered shell at the NP surface. The presence of two peaks in the temperature dependence of both the dc magnetization after zero-field-cooling and the real part of the ac magnetic susceptibility is explained in terms of a core (antiferromagnetic, AFM)/shell (spin glass, SG) morphology. The high-temperature peak ([Formula: see text] K) is associated with collective blocking of the uncompensated magnetic moments inside the AFM core. The low-temperature peak ([Formula: see text] K) is a signature of a SG-like freezing of the surface [Formula: see text] spins. In addition, an exchange bias (EB) effect emerges due to the core/shell magnetic coupling. The cooling field and temperature dependences of the EB effect and the coercive field are discussed in terms of the core size and the effective magnetic anisotropy of the NPs. However, NiO NPs of 2 nm in size no longer show AFM order and the [Formula: see text] magnetic moments freeze into a SG-like state below [Formula: see text] K, with no evidence of EB effect.
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Affiliation(s)
- N Rinaldi-Montes
- Departamento de Física, Universidad de Oviedo, E-33007 Oviedo, Spain
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Zhou NJ, Zheng B. Nonequilibrium critical dynamics with domain wall and surface. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:051104. [PMID: 18643023 DOI: 10.1103/physreve.77.051104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Indexed: 05/26/2023]
Abstract
With Monte Carlo simulations, we investigate the relaxation dynamics with a domain wall for magnetic systems at the critical temperature. The dynamic scaling behavior is carefully analyzed, and a dynamic roughening process is observed. For comparison, similar analysis is applied to the relaxation dynamics with a free or disordered surface.
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Affiliation(s)
- N J Zhou
- Zhejiang University, Zhejiang Institute of Modern Physics, Hangzhou 310027, People's Republic of China
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Nakamura T, Endoh SI, Yamamoto T. Weak universality of spin-glass transitions in three-dimensional ±Jmodels. ACTA ACUST UNITED AC 2003. [DOI: 10.1088/0305-4470/36/43/015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Zheng B, Ren F, Ren H. Corrections to scaling in two-dimensional dynamic XY and fully frustrated XY models. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:046120. [PMID: 14683015 DOI: 10.1103/physreve.68.046120] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2003] [Indexed: 05/24/2023]
Abstract
With large-scale Monte Carlo simulations, we investigate the two-dimensional dynamic XY and fully frustrated XY models. Dynamic relaxation starting from a disordered or an ordered state is carefully analyzed. It is confirmed that there is a logarithmic correction to scaling for a disordered start, but a power-law correction for an ordered start. Rather accurate values of the static exponent eta and the dynamic exponent z are estimated.
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Affiliation(s)
- B Zheng
- Physics Department, Zhejiang University, Hangzhou 310027, People's Republic of China
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Zheng B, Luo HJ. Monte Carlo simulations of short-time critical dynamics with a conserved quantity. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:066130. [PMID: 11415196 DOI: 10.1103/physreve.63.066130] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2000] [Indexed: 05/23/2023]
Abstract
With Monte Carlo simulations, we investigate short-time critical dynamics of the three-dimensional antiferromagnetic Ising model with a globally conserved magnetization m(s) (not the order parameter). From the power law behavior of the staggered magnetization (the order parameter), its second moment and the autocorrelation, we determine all static and dynamic critical exponents as well as the critical temperature. The universality class of m(s)=0 is the same as that without a conserved quantity, but the universality class of nonzero m(s) is different.
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Affiliation(s)
- B Zheng
- FB Physik, Universität Halle, D-06099 Halle, Germany
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Ying HP, Zheng B, Yu Y, Trimper S. Corrections to scaling for the two-dimensional dynamic XY model. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:035101. [PMID: 11308695 DOI: 10.1103/physreve.63.035101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2000] [Indexed: 05/23/2023]
Abstract
With large-scale Monte Carlo simulations, we confirm that for the two-dimensional XY model, there is a logarithmic correction to scaling in the dynamic relaxation starting from a completely disordered state, while only an inverse power law correction in the case of starting from an ordered state. The dynamic exponent z is z=2.04(1).
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Affiliation(s)
- H P Ying
- Zhejiang Institute of Modern Physics, Zhejiang University, Hangzhou 310027, People's Republic of China
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Bray AJ. Random walks in logarithmic and power-law potentials, nonuniversal persistence, and vortex dynamics in the two-dimensional XY model. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:103-112. [PMID: 11088441 DOI: 10.1103/physreve.62.103] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/1999] [Indexed: 05/23/2023]
Abstract
The Langevin equation for a particle ("random walker") moving in d-dimensional space under an attractive central force and driven by a Gaussian white noise is considered for the case of a power-law force, F(r) approximately -r(-sigma). The "persistence probability," P0(t), that the particle has not visited the origin up to time t is calculated for a number of cases. For sigma>1, the force is asymptotically irrelevant (with respect to the noise), and the asymptotics of P0(t) are those of a free random walker. For sigma<1, the noise is (dangerously) irrelevant and the asymptotics of P0(t) can be extracted from a weak noise limit within a path-integral formalism employing the Onsager-Machlup functional. The case sigma=1, corresponding to a logarithmic potential, is most interesting because the noise is exactly marginal. In this case, P0(t) decays as a power law, P0(t) approximately t(-straight theta) with an exponent straight theta that depends continuously on the ratio of the strength of the potential to the strength of the noise. This case, with d=2, is relevant to the annihilation dynamics of a vortex-antivortex pair in the two-dimensional XY model. Although the noise is multiplicative in the latter case, the relevant Langevin equation can be transformed to the standard form discussed in the first part of the paper. The mean annihilation time for a pair initially separated by r is given by t(r) approximately r(2) ln(r/a) where a is a microscopic cutoff (the vortex core size). Implications for the nonequilibrium critical dynamics of the system are discussed and compared to numerical simulation results.
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Affiliation(s)
- AJ Bray
- Department of Physics and Astronomy, The University, Manchester M13 9PL, United Kingdom
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Bray AJ, Briant AJ, Jervis DK. Breakdown of scaling in the nonequilibrium critical dynamics of the two-dimensional XY model. PHYSICAL REVIEW LETTERS 2000; 84:1503-1506. [PMID: 11017553 DOI: 10.1103/physrevlett.84.1503] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/1999] [Indexed: 05/23/2023]
Abstract
The approach to equilibrium, from a nonequilibrium initial state, in a system at its critical point is usually described by a scaling theory with a single growing length scale, xi(t) approximately t(1/z), where z is the dynamic exponent that governs the equilibrium dynamics. We show that, for the 2D XY model, the rate of approach to equilibrium depends on the initial condition. In particular, xi(t) approximately t(1/2) if no free vortices are present in the initial state, while xi(t) approximately (t/lnt)(1/2) if free vortices are present.
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Affiliation(s)
- AJ Bray
- Department of Physics and Astronomy, The University, Manchester, M13 9PL, United Kingdom
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Parisi G, Picco M, Ritort F. Continuous phase transition in a spin-glass model without time-reversal symmetry. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:58-68. [PMID: 11969737 DOI: 10.1103/physreve.60.58] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/1998] [Indexed: 04/18/2023]
Abstract
We investigate the phase transition in a strongly disordered short-range three-spin interaction model characterized by the absence of time-reversal symmetry in the Hamiltonian. In the mean-field limit the model is well described by the Adam-Gibbs-DiMarzio scenario for the glass transition; however, in the short-range case this picture turns out to be modified. The model presents a finite temperature continuous phase transition characterized by a divergent spin-glass susceptibility and a negative specific-heat exponent. We expect the nature of the transition in this three-spin model to be the same as the transition in the Edwards-Anderson model in a magnetic field, with the advantage that the strong crossover effects present in the latter case are absent.
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Affiliation(s)
- G Parisi
- Dipartimento di Fisica and INFN, Universita di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy.
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Menyhárd N, Ódor G. Non-Markovian persistence at the parity conserving point of a one-dimensional nonequilibrium kinetic Ising model. ACTA ACUST UNITED AC 1999. [DOI: 10.1088/0305-4470/30/24/015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Rieger H. Nonequilibrium dynamics and aging in the three-dimensional Ising spin-glass model. ACTA ACUST UNITED AC 1999. [DOI: 10.1088/0305-4470/26/15/001] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Ciria JC, Parisi G, Ritort F. Four-dimensional Ising spin glass: scaling within the spin-glass phase. ACTA ACUST UNITED AC 1999. [DOI: 10.1088/0305-4470/26/23/021] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Menyhárd N, Ódor G. Phase transitions and critical behaviour in one-dimensional non-equilibrium kinetic Ising models with branching annihilating random walk of kinks. ACTA ACUST UNITED AC 1999. [DOI: 10.1088/0305-4470/29/23/030] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Li Z, Schülke L, Zheng B. Finite-size scaling and critical exponents in critical relaxation. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:2940-2948. [PMID: 9964582 DOI: 10.1103/physreve.53.2940] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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