Intrinsic magnetic relaxation in goethite

Pankhurst, Quentin A.; Barquı́n, L. Fernández; Lord, J. S.; Amato, A.; Zimmermann, U.

doi:10.1103/physrevb.85.174437

Cited by 17 publications

(23 citation statements)

References 52 publications

(78 reference statements)

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“…Our conclusion is further supported by the temperature evolution of the distribution of magnetic hyperfine fields, which is known to provide valuable clues on the spin arrangement 26,29,[49][50][51] . The distributions determined for PFN are shown in Fig.…”

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confidence: 59%

Microscopic coexistence of antiferromagnetic and spin-glass states

et al. 2013

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The disordered antiferromagnet PbFe 1/2 Nb 1/2 O3 (PFN ) is investigated in a wide temperature range by combining Mössbauer spectroscopy and neutron diffraction experiments. It is demonstrated that the magnetic ground state is a microscopic coexistence of antiferromagnetic and a spin-glass orders. This speromagnet-like phase features frozen-in short-range fluctuations of the Fe 3+ magnetic moments that are transverse to the long-range ordered antiferromagnetic spin component.Phase transitions in the presence of disorder and/or competing interactions are one of the central unresolved problems in modern condensed matter physics 1-4 . With both effects present, one may encounter a freezing of microscopic degrees of freedom without conventional longrange order. In magnetic systems, the corresponding phenomenon is referred to as a spin-glass (SG) transition 5 . By now, spin glasses are reasonably well understood for models with discrete (Ising) symmetries and long-range interactions 6,7 . In contrast, for continuous (Heisenberg and XY) symmetries with short-range coupling, the properties and sometimes the very existence of the SG phase remain a matter of debate [8][9][10][11][12] . An important outstanding question is whether the SG phase can coexist with true long-range order (LRO) 12,13 ? Theory 14-16 and numerical studies 17-20 have consistently provide an affirmative answer; see Ref.21 for a review. Both ferromagnetic (FM) 15 and AF 16 models demonstrate a SG freezing of spin components transverse to the long range order parameter. The problem gained a particular urgency in the context of cuprate superconductors, where SG and AF phases are adjacent on the concentrationtemperature phase diagram but appear to be mutually exclusive 22,23 .On the experimental side though, the situation is much less clear-cut and hotly debated. Most hurdles on this route are the known measurement issues endemic to spin glasses 1,24,25 . In addition, even if long range order and SG are shown to appear simultaneously, it may be extremely difficult to establish their co-existence on the microscopic scale, as opposed to an inhomogeneous phase separation. A great deal of work was done on amorphous, ferromagnetic Fe X Zr 100−X alloys. While strong support for uniformly coexisting SG and LRO in these systems have been presented 20,[26][27][28] , evidence pointing to a cluster-based scenario also exist 29 . In crystalline materials, simultaneous antiferromagnetic (AF) and SG states have been observed in Fe 0.6 Mn 0.4 TiO 3 30,31 and Co 2 (OH)PO 4 32 . However, even in these Ising systems, the microscopic nature of such coexistence is not unambiguous 31,32 .A solid experimental proof of microscopic SG and LRO coexistence in a crystalline material remains elu- sive. Besides finding an appropriate model compound, one has to strategically choose the experimental techniques. Momentum-resolved (scattering) experiments are well-suited to probe microscopic quantities averaged over the entire sample, but do not provide spatiallyresolved information. I...

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confidence: 59%

Microscopic coexistence of antiferromagnetic and spin-glass states

et al. 2013

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“…67 Very recently it has been shown that goethite properties are dominated by the AFM order, followed by a lower transition in the fine particle state, and a further very low temperature magnetic coupling mode. 68,69 In essence, this Fe oxihydroxide turns out as a macroscopically very similar system to nano-TbCu 2 . Therefore, the study of SAFM R-based nanoparticles allow to extract information on the surface moments given that the particle cores have a negligible response as reported in Fe-oxides.…”

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confidence: 99%

Magnetic phase diagram of superantiferromagnetic TbCu₂nanoparticles

Echevarria-Bonet

Rojas

Espeso

et al. 2015

J. Phys.: Condens. Matter

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The structural state and static and dynamic magnetic properties of TbCu2 nanoparticles are reported. The nanoparticles were produced by mechanical milling under inert atmosphere with low milling times ≤ 15 hours. The randomly dispersed nanoparticles as detected by TEM retain the bulk symmetry with an orthorhombic Imma lattice and Tb and Cu in 4c positions. Rietveld refinements confirm that the milling produces a controlled reduction of particle sizes reaching down to ≃ 6 nm and an increase of the microstrain ≃ 0.6 %. The DC-susceptibility shows a reduction of the Néel transition (from 49 K to 43 K) and a progressive increase of the spin glass peak (from 9 to 15 K) in the zero field cooled magnetization with size reduction. The exchange anisotropy is very weak (bias field of ≃ 30 Oe) and is due to the presence of a disordered (thin) shell coupled to the antiferromagnetic core. The dynamic susceptibility evidences a critical slowing down in the spin disordered state with a tendency to increase of zv and β exponents when the size becomes smaller (zv ≃ 6.6 and β ≃ 0.85). A Rietveld analysis of neutron diffraction patterns 1.8 ≤ T ≤ 60 K including the magnetic structure determination reveals that there is a reduction of the expected moment (≃ 80 %) which must be connected to the presence of the disordered particle shell. The core magnetic structure retains the bulk antiferromagnetic arrangement. The overall interpretation is based on a superantiferromagnetic behavior which at low temperatures coexists with a canting of surface moments. We propose a novel magnetic phase diagram as a function of the particle size.

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“…The crystal structure of goethite is orthorhombic with space group Pnma. The magnetic properties of goethite have been studied extensively by Mössbauer spectroscopy, [1][2][3][4][5][6][7][8][9][10][11] magnetization measurements [9,11,12] and neutron scattering. [1,11,13,14] The magnetic properties of nanocrystalline goethite samples often differ from those of non-interacting nanoparticles.…”

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confidence: 99%

Anomalous Particle Size Dependence of Magnetic Relaxation Phenomena in Goethite Nanoparticles

Frandsen¹,

Madsen²,

Boothroyd³

et al. 2015

Croat. Chem. Acta

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By use of Mössbauer spectroscopy we have studied the magnetic properties of samples of goethite nanoparticles with different particle size. The spectra are influenced by fluctuations of the magnetization directions, but the size dependence is not in accordance with the Néel-Brown expression for superparamagnetic relaxation of the magnetization vectors of the particles as a whole. The data suggest that the magnetic fluctuations can be explained by fluctuations of the magnetization directions of small interacting grains within the particles.

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Intrinsic magnetic relaxation in goethite

Cited by 17 publications

References 52 publications

Microscopic coexistence of antiferromagnetic and spin-glass states

Microscopic coexistence of antiferromagnetic and spin-glass states

Magnetic phase diagram of superantiferromagnetic TbCu₂nanoparticles

Anomalous Particle Size Dependence of Magnetic Relaxation Phenomena in Goethite Nanoparticles

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Intrinsic magnetic relaxation in goethite

Cited by 17 publications

References 52 publications

Microscopic coexistence of antiferromagnetic and spin-glass states

Microscopic coexistence of antiferromagnetic and spin-glass states

Magnetic phase diagram of superantiferromagnetic TbCu2nanoparticles

Anomalous Particle Size Dependence of Magnetic Relaxation Phenomena in Goethite Nanoparticles

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Magnetic phase diagram of superantiferromagnetic TbCu₂nanoparticles