Chapter 206 μSR studies of rare-earth and actinide magnetic materials

Kalvius, Georg Michael; Noakes, D. R.; Hartmann, O.

doi:10.1016/s0168-1273(01)32005-6

Cited by 65 publications

(62 citation statements)

References 1,123 publications

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“…The temperature dependence of λ is indicative of a sharp magnetic ordering phase transition at T c ∼ 12.5 K, where the increase as T approaches T c from above is due to critical slowing down of the fluctuations. The relaxation at low temperatures is attributed to remnant local field fluctuations due to spin wave excitations [18]. Both λ and ∆ temperature dependencies are in agreement with the ferrimagnetic behavior seen in the magnetization measurements.…”

Section: B Experimentalsupporting

confidence: 81%

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Muon spin relaxation study of the magnetism in unilluminated Prussian Blue analogue photomagnets

et al. 2006

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We present longitudinal field muon spin relaxation (µSR) measurements in the unilluminated state of the photo-sensitive molecular magnetic Co-Fe Prussian blue analogues M1−2xCo1+x[Fe(CN)6]·zH2O, where M=K and Rb with x = 0.4 and ≃ 0.17, respectively. These results are compared to those obtained in the x = 0.5 stoichiometric limit, Co1.5[Fe(CN)6]·6 H2O, which is not photo-sensitive. We find evidence for correlation between the range of magnetic ordering and the value of x in the unilluminated state which can be explained using a site percolation model. A. IntroductionPrussian Blue (PB) (Fe 4 [Fe(CN) 6 ] 3 ) is a long-known dye and prototypical transition metal co-ordination compound that exhibits ferro-magnetism [1,2,3] driven by superexchange coupling between iron spins. It is an important case of exchange coupling mediated through the CN − bridge [4]. Much of the recent interest in magnetic compounds related to PB (including a few that have been studied with µSR [5,6,7]) is motivated by potential novel behavior and related applications in molecular magnetism [8,9], including magnetism that is sensitive to exposure to light, i.e. photomagnetism.The compounds studied in this paper are the molecule based Co-Fe PB analogues (Co-Fe PBAs)1: (Color online) Crystal structure of M1−2xCo1+x[Fe(CN)6]·zH2O: (a) x = 0.5; (b) x = 0.5, with an Fe(CN)6 vacancy shown in gray coordinated by bound water molecules. Large, medium and small circles denote Fe, Co, and CN, respectively. The alkali ions which maintain charge neutrality occupy cubic interstitial sites (not shown).1 This chemical formula is a commonly used approximation though [8,9,12]. These compounds have the sodium chloride structure, with Co and Fe ions located on the vertices of a cubic lattice, each octahedrally coordinated by six cyano moieties (Fig. 1). The Co and Fe ions are connected via cyanide bridges with interstitial alkali metal ions and water molecules [9,13] (Fig. 1(b)). Co-Fe PBAs are in general non-stoichiometric and significant structural disorder (vacancies in the Fe(CN) 6 sites) is present. Depending on the stoichiometry and synthesis route, the materials are paramagnets or exhibit magnetic ordering at temperatures below ∼ 25 K, due to small superexchange coupling J between Fe III and Co II moments.Illumination of Co-Fe PBAs with broadband visible light in the range of ∼ 550 − 750 nm can cause dramatic changes in the magnetic properties, including an increase in magnetization and ordering temperature. The proposed origin of the photomagnetic effect is a light-induced charge transfer from the state: Fe II (t 6 2g , S = 0)-CNCo III (t 6 2g , S = 0) to the meta-stable self-trapped state: Fe III (t 5 2g , S = 1/2)-CN-Co II (t 5 2g e 2 g , S = 3/2) [9,14], effectively increasing the concentration of magnetic moments. The non-stoichiometry is believed essential for the photoinduced magnetization [14]. However, in spite of considerable experimental and theoretical effort, the microscopic mechanism of the photomagnetic effect and the nature of magnetic orde...

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Section: B Experimentalsupporting

confidence: 81%

“…An extensive review of µSR in magnetic materials is given in Ref. [18]. Further details on the µSR technique may be found in Refs.…”

Section: B Experimentalmentioning

confidence: 99%

Muon spin relaxation study of the magnetism in unilluminated Prussian Blue analogue photomagnets

et al. 2006

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“…Stronger magnetic correlations between the spins slow down the spin fluctuations which leads to a remarkable rise in the relaxation rate. 28,36 Thus, our μSR results indicate the formation of short-range-order correlations below T * . These dynamic magnetic clusters are responsible for a muon spin relaxation rate (λ fast ) which is about two orders of magnitude higher than the decay due to the paramagnetic fluctuations in ErCo 2 .…”

Section: B Paramagnetic Regimementioning

confidence: 50%

“…28 Therefore, we will present our analysis of the spectra recorded below and above T c in two independent subsections.…”

Section: Resultsmentioning

confidence: 99%

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μSR study of short-range magnetic order in the paramagnetic regime of ErCo2

et al. 2011

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Zero-field muon spin relaxation spectroscopy (μSR) measurements in the paramagnetic phase of ErCo 2 ferrimagnetic system are reported. Previous experimental studies using macro-and microscopic techniques led to the identification of magnetic short-range correlations between the Co atoms in the paramagnetic state of this material. The analysis of μSR spectra recorded on ErCo 2 well above T c indicates two dynamical magnetic processes characterized by remarkably different relaxation rates: a slow-relaxing signal, which quantitatively coincides with previous μSR studies on ErAl 2 , and fast-relaxing signal, which can be ascribed to the Co short-range correlated regions observed above T c . Moreover, the μSR technique provides information on the thermal dependence of Co correlated regions at true zero field. These findings shed light on the dynamical nature of the clustered phase developing in the paramagnetic state of ErCo 2 .

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