57Fe Mössbauer effect studies of the point defects structure in fast neutron irradiated garnet ferrites Y3Fe5−xAlxO12

Sinitsin, S. V.; Spirin, N. А.; Uspensky, M. N.

doi:10.1007/bf02399453

Cited by 11 publications

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“…We explain the new transition by this specific distribution of radiation defects. It must be noted that Goshchitskii et al [ll] and Sinitsin et al [14] investigated the structure and magnetic properties of magnetic oxides irradiated with neutrons and observed superparamagnetic behaviour of DM. It means that the direction of the mean magnetic moment of DM under the condition K,T 9 KeffV (Keff is the effective anisotropy constant, V the volume of the microregion), undergoes thermal fluctuations similarly to the magnetic moment of a separate cation in the paramagnetic region.…”

Section: Resultsmentioning

confidence: 99%

New Spin‐Reorientation Transition in Irradiated Single Crystal Hematite

Donbaev

Zhetbaev

Mukusheva

1993

Physica Status Solidi (b)

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It is experimentally observed that irradiation of single crystal hematite Fe,O, leads to a decrease of the Morin spin-reorientation transition temperature and to the appearance of a reverse transition, i.e. to recovery of a weakly ferromagnetic phase at very low temperatures. Parameters of the new transition depend on the type and energy of particles. The possible reasons for the new transition and the formation mechanism of the disordered zones produced by atom-atom collision cascades are discussed. The splitting of the Mossbauer spectra in the temperature interval of the new transition undoubtedly shows that it is a first-order transition. 3KCnepHMeHTanbHO 06HapyXeH0, YTO 06~1yYeHWe MOHOKpUCTannOB reMaTATa Fe,O, IIpWBOnAT K CHIIXCHWIO TeMnepaTypbI CnWH-nepeOpIleHTarrIloHHoro nepeXOna Mopma W B03HWKHOBeHAIO 06-PaTHOrO nepCXOna, T. e. BOCCTdHOBJIeHAIO CJId60@eppOMarHHTHOfi @a361 IIpH OYeHb HW3KWX TeMnepa-TypaX. napaMeTpb1 HOBOrO IIepeXOna 3aBWCIlT OT TWna W 3HeprWA YaCTWU. 06cywnam~cs BO3MOXHbIe nPW4WHbl BOSHAKHOBeHUX HOBOrO IICpeXOAa, MeXaHIl3M B03HWKHOBeHIIR 3 0 H pa3ynOPIlAOYeHUIl, COSfiaHHbIX K a C K a n O M aTOM-ZTOMHbIX CTOJIKHOBeHA€%. PaCWenJIeHAe MeCC6ay3pOBCKIIX CneKTpOB B o 6 n a c~~ HOBOrO IIepeXOnd OAHOJHBYHO IIOKa3bIBaCT, YTO OH IlBJIReTCIl IIepeXOflOM I POW.') 480082 Alma-Ata, Republic of Kazakhstan.

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Section: Resultsmentioning

confidence: 99%

New Spin‐Reorientation Transition in Irradiated Single Crystal Hematite

Donbaev

Zhetbaev

Mukusheva

1993

Physica Status Solidi (b)

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“…by shock waves or irradiation. Then, the relative volumes occupied by each structure, or the structure probabilities, are additional thermodynamic variables which can be defined experimentally by different means, for example by nuclear gamma resonance [4,5]. Probably, the most promising application of this approach is to considering substances with thermal structural fluctuations.…”

Section: Discussionmentioning

confidence: 99%

“…For a statistical description of an irradiated crystal the defected regions can be treated as embryos of disordered, usually rarefied, phase inside an ordered, more dense, crystalline structure [2,3]. The relative volume occupied by the disordered phase can be measured, with a good accuracy, by investigating the nuclear gamma resonance spectra and the behavior of the Mössbauer factor [4,5].In the considered examples the germs of a disordered structure are randomly distributed in space inside an ordered structure. This is why these germs can be called the spatial structural fluctuations.…”

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confidence: 99%

“…Quantum crystals exhibit near phase transition points the well observed fluctuational coexistence of competing structures. This takes place, for example, in solid 4 He along the line of the structural transition between h.c.p. and b.c.c.…”

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confidence: 99%

“…and b.c.c. phases and also in the solid mixture of 4 He with 3 He along the stratification line [20]. These local fluctuational effects involve usually about 100 particles.…”

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Statistical mechanics of structural fluctuations

Yukalov

1995

Physica A: Statistical Mechanics and its Applications

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The theory of mesoscopic fluctuations is applied to inhomogeneous solids consisting of chaotically distributed regions with different crystalline structure. This approach makes it possible to describe statistical properties of such mixture by constructing a renormalized Hamiltonian. The relative volumes occupied by each of the coexisting structures define the corresponding geometric probabilities. In the case of a frozen heterophase system these probabilities should be given a priori. And in the case of a thermal heterophase mixture the structural probabilities are to be defined self-consistently by minimizing a thermodynamical potential. This permits to find the temperature behavior of the probabilities which is especially important near the points of structural phase transitions. The presense of these structural fluctuations yields a softening of a crystal and a decrease of the effective Debye temperature. These effects can be directly seen by nuclear gamma resonance since the occurrence of structural fluctuations is accompanied by a noticeable sagging of the Mössbauer factor at the point of structural phase transition. The structural fluctuations also lead to the attenuation of sound and increase of isothermic compressibility. I. INTRODUCTIONThere are many examples of matter consisting of regions, chaotically distributed in space, with different structural properties. For instance, such are some polymorphic materials. Another example is a crystal subject to strong mechanical stress after which the cracks and branches of dislocation are formed in it. These defects have a tendency to group inside compact regions. The latter, from the point of view of statistical physics, can be treated as nuclei of the amorphised phase inside a crystalline matrix [1]. A similar picture develops in crystals under the action of irradiation by fast neutrons when the pores and regions of disorder arise. Under strong irradiation cracks also appear. These defects form groups and clusters randomly distributed in space, e.g. as is shown in Figs. 1 and 2. For a statistical description of an irradiated crystal the defected regions can be treated as embryos of disordered, usually rarefied, phase inside an ordered, more dense, crystalline structure [2,3]. The relative volume occupied by the disordered phase can be measured, with a good accuracy, by investigating the nuclear gamma resonance spectra and the behavior of the Mössbauer factor [4,5].In the considered examples the germs of a disordered structure are randomly distributed in space inside an ordered structure. This is why these germs can be called the spatial structural fluctuations. With respect to time, they are frozen, which means that their average lifetime, τ f , is much longer than the characteristic time of an experiment, or the observation time, τ obs , that is: τ f ≫ τ obs . In the opposite case, when τ f ≪ τ obs , we have thermal structural fluctuations. The example of the latter are even more numerous than those of the frozen structural fluctuations.Water, the most widespr...

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Peculiairities of Magnetic Properties of the Garnet Y2.25Gd0.75Fe5O12 Irradiated by Fast Neutrons

Chukalkin

Shtirts

1999

phys. stat. sol. (a)

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Polycrystalline yttrium‐gadolinium iron garnet samples irradiated by different fluences of fast neutrons ((0 to 2.0) × 1024 m—2 were investigated by magnetic and X‐ray methods. Irradiation was found to increase the temperature of sublattice magnetization compensation from 5 to 47 K. The increase was attributed to the different behaviour of gadolinium and iron sublattices under irradiation. In the irradiated samples negative magnetization states were found to arise in the vicinity of the compensation point. The phase H—T diagram of such states was plotted based on the measurements performed. The cause of a negative magnetization occurrence was shown to be the intersection of a spin reorientation with respect to temperature in the compensation point and a freezing of magnetic moments of ferrimagnetic clusters in a spin‐glass matrix.

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57Fe Mössbauer effect studies of the point defects structure in fast neutron irradiated garnet ferrites Y3Fe5−xAlxO12

Cited by 11 publications

References 2 publications

New Spin‐Reorientation Transition in Irradiated Single Crystal Hematite

New Spin‐Reorientation Transition in Irradiated Single Crystal Hematite

Statistical mechanics of structural fluctuations

Peculiairities of Magnetic Properties of the Garnet Y2.25Gd0.75Fe5O12 Irradiated by Fast Neutrons

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