Resonance magnetoplasticity in ultralow magnetic fields

Ivanova E.S., Rumyantsev I.D., Petrzhik E.A.

The effect of a constant magnetic field on the dielectric properties of triglycine sulfate crystals has been investigated. It has been shown that, after the magnetic treatment of the crystal (2 T, 20 min), the hysteresis loop becomes narrower; i.e., the coercive field decreases, and the dielectric permittivity changes in the region of the phase transition. It has been found that the observed effect is anisotropic with respect to the orientation of the crystal in a magnetic field and occurs when the vector of magnetic induction is perpendicular to the polar axis of the crystal. The relative orientation of the magnetic field and the domain structure determines its sign. The doping of the crystal with chromium makes the effect more pronounced and leads to a change in the kinetics of the magnetically stimulated increase in the dielectric permittivity.

Alshits V.I., Darinskaya E.V., Koldaeva M.V., Petrzhik E.A.

A comparative study of magnetoplasticity in two types of NaCl crystals differing in impurity content only by a small Ni addition (0.06 ppm) in one of them, NaCl(Ni), has been carried out. Two methods of sample magnetic exposure were used: in a constant field B = 0–0.6 T and in crossed fields in the EPR scheme—the Earth’s field B Earth (50 μT) and a variable pumping field $$\tilde B( \sim 1 \mu T)$$ at frequencies ν ~ 1 MHz. In the experiments in the EPR scheme, the change of the field orientation from $$\tilde B \bot B_{Earth}$$ to $$\left. {\tilde B} \right\|B_{Earth}$$ led to almost complete suppression of the effect in the NaCl(Ni) crystals and reduced only slightly (approximately by 20%) the height of the resonance peak of dislocation mean paths in the crystals without Ni, with the amplitude of the mean paths in NaCl(Ni) in the orientation $$\tilde B \bot B_{Earth}$$ having been appreciably lower than that in NaCl. In contrast, upon exposure to a constant magnetic field, a more intense effect was observed in the crystal with Ni. The threshold pumping field amplitude $$\tilde B$$ , below which the effect is absent under resonance conditions, for the NaCl(Ni) crystals turned out to be a factor of 5 smaller than that for NaCl, while the thresholds of a constant magnetic field coincide for both types of crystals. All these differences are discussed in detail and interpreted.

Petrzhik E.A., Ivanova E.S., Alshits V.I.

Changes are found in the microhardness and dielectric permittivity of triglycine sulfate (TGS) crystals after magnetic treatment in a permanent magnetic field or in the scheme of electron paramagnetic resonance (EPR) using the Earth’s magnetic field. The temporal kinetics of microhardness reduction and the rise in dielectric permittivity (as along with their recovery) are nearly identical. The effects disappear when the crystal’s axis of symmetry is parallel to the static magnetic field in both variants of exposure.

Koldaeva M.V., Alshits V.I., Petrzhik E.A., Darinskaya E.V., Belov A.Y.

It is shown that the criterion of dislocation mobility resonance in NaCl crystals in the electron spin resonance scheme in the Earth’s magnetic field depends on both the sample orientation in this field and the location of impurity atoms in the dislocation core. The measured low-frequency spectrum of dislocation paths makes it possible to resolve a series of peaks corresponding to different positions of a Ca impurity that correlate with the results from computer simulations of the dislocation core structure.

Alshits V.I., Darinskaya E.V., Koldaeva M.V., Minyukov S.A., Petrzhik E.A., Morozov V.A., Kats V.M., Lukin A.A., Naimi E.K.

Resonance relaxation displacements of dislocations in NaCl crystals exposed to crossed ultralow magnetic fields (static field B = 26–261 μT and radiofrequency field B ∼ 3 μT) in the electron paramagnetic resonance scheme are studied. The effect is also observed in the magnetic field of the Earth when crossed with a pulsed pump field with a resonance duration of ∼0.5 μs. Changes in the microhardness of crystals of ZnO, triglycine sulfate, and potassium hydrogen phthalate after their exposure to the magnetic field of the Earth and the orthogonally directed pump field are found out.

Alshits V.I., Koldaeva M.V., Petrzhik E.A., Belov A.Y., Darinskaya E.V.

The spectra of the mean free paths l(ν) of edge dislocations have been studied in NaCl crystals exposed in the electron paramagnetic resonance scheme to the crossed magnetic fields: the Earth’s field (50 μT) and the pump field (2.5 μT, 5–440 kHz). The spectra have been measured for a series of angles θ = 0°–5° of rotation of the sample around its edge [100] with respect to the Earth’s field. The fine structure of the spectra contains a series of peaks whose resonance frequencies are described by the empirical expression v ± = Asin(θ ± Δθ i ) ≈ A(θ ± Δθ i ). The parameters Δθ i are independent of the angle θ within the experimental errors. Within the model of “frozen” magnetic moments associated with impurity center Ca+-Cl0, the angles Δθ i characterize the deviation of the axis of the center from the 〈100〉 direction in the core of a dislocation. These angles can be expressed in terms of the spectra obtained: Δθ i = (− + − v − )/2A. The computer simulation of the edge dislocation core provides the set of the angles Δθ i close to the measured values. The spin-lattice relaxation time of the center on dislocation has been estimated from the low-frequency edge of the spectrum l(ν) as τ s − l ∼ 10−4 s.

Alshits V.I., Darinskaya E.V., Morozov V.A., Kats V.M., Lukin A.A.

Resonant dislocation motions in NaCl(Ca) crystals under the simultaneous action of the Earth’s magnetic field B Earth (∼66 μT) and a pulsed pump field $\tilde B$ of sufficient amplitude $\tilde B_m $ and certain duration τ have been detected and studied. The measured dislocation path peaks l(τ) have a maximum at τ = τ r ≈ 0.53 μs. The resonance criterion has been found to be the ordinary EPR condition in which the g-factor is close to 2 and the optimum inverse pulse duration τ −1 is used instead of the harmonic pump field frequency ν r . The largest peak l(τ) height is reached at mutually orthogonal dislocation (L) and magnetic field (B Earth and $\tilde B$ ) orientations. Pulsed field rotation to the position $\tilde B$ ‖ B Earth significantly decreases but does not “kill” the effect. For dislocations parallel to the Earth’s field (L ‖ B Earth), the resonance almost disappears even at $\tilde B$ ⊥ B Earth. In the optimum geometry of experiments, as the pump field amplitude $\tilde B_m $ decreases from 17.6 to 10 μT, the path peak height l r = l(τ r ) decreases only by 7.5%, remaining at the level of l r ∼ 102 μm, and at a $\tilde B_m $ further fall-off to 4 μT, it rapidly decreases to background values. In this case, the relative density of mobile dislocations similarly decreases from ∼90 to 40%. Possible physical mechanisms of the observed effect have been discussed.

Alshits V.I., Koldaeva M.V., Petrzhik E.A., Minyukov S.A., Darinskaya E.V., Kaputkin D.E., Naimi E.K.

Resonance relaxation displacements of dislocations have been studied in NaCl crystals placed in crossed ultralow magnetic fields have been studied in the electron paramagnetic resonance (EPR) scheme, i.e., in the static magnetic field B = (26–261) μT and the perpendicular radio-frequency field (with the amplitudes of 2.5 and 6 μT in the frequency range ν = (0.5–7.3) MHz). The spectrum (quartet) of equidistant resonance peaks of the dislocation mean paths l(ν) has been observed. In the most part of the studied field interval B, the frequencies of the EPR peaks correspond to the Zeeman splitting of the levels with four g-factors close to 2 and the difference of the neighboring values Δg = 0.09. The equidistance is violated only at the lowest fields, B < 50 μT, and frequencies ν < 0.7 MHz.

Alshits V.I., Darinskaya E.V., Koldaeva M.V., Petrzhik E.A.

Resonant relaxation of the dislocation structure under the action of crossed magnetic fields, i.e., constant magnetic field of the Earth (B Earth) and alternating radio-frequency field ( $\tilde B$ ), has been experimentally studied in a series of dielectric (NaCl) crystals with various compositions of impurities under variations in the frequency, direction of the pumping field $\tilde B$ , and orientation of the samples in the Earth’s magnetic field. The frequency dependence of the dislocation path length l(ν) exhibits peaks with various heights (l max) and resonant frequencies (νres). The maximum resonant effect has been observed for dislocations with the direction L orthogonal to the plane of crossed magnetic fields in a configuration of mutually perpendicular vectors {L, $\tilde B$ , B Earth} belonging, together with sample edges {a, b, c}, to the 〈100〉 system. Variation of the concentration C of calcium impurity in crystals of the NaClCa series only influenced the resonant peak height as $l_{\max } \propto 1/\sqrt C $ . Rotation of the magnetic field $\tilde B$ in the (b, c) plane from direction $\tilde B$ ⊥ B Earth to $\tilde B$ ∥ B Earth also did not influence the frequency of the resonance but changed its amplitude. Depending on the crystal type, this influence changed from rather insignificant (in crystals of the NaClLOMO series) to complete suppression of the effect for $\tilde B$ ∥ B Earth (in the NaClNik series). The resonant frequency νres is sensitive to orientation of the sample with respect to B Earth. Upon rotation of the crystal by the angle θ = ∠(c, B Earth) about the a ⊥ B Earth edge, the initial peak for dislocations L ‖ a at the crystal orientation θ = 0 and the frequency ν res 0 is replaced by a pair of peaks at frequencies ν1, 2 ≈ ν res 0 cosθ1, 2, where θ1 = 90° − θ and θ2 = θ. Previously, these peaks were observed separately in NaClNik crystals for $\tilde B$ ∥ c and $\tilde B$ ∥ b. In the present study, these peaks have been observed simultaneously for both orientations of $\tilde B$ in NaClLOMO and NaClCa crystals, where the resonance is not completely suppressed for $\tilde B$ ∥ B Earth.

Alshits V.I., Darinskaya E.V., Koldaeva M.V., Petrzhik E.A.

Changes in the microhardness of ZnO, triglycine sulfate (TGS), and potassium acid phthalate (KAP) crystals after their exposure to crossed ultralow magnetic fields, i.e., the Earth’s field B Earth ≈ 50 μT and the alternating-current field $$\tilde B \approx 3 \mu {\rm T}$$ orthogonal to it, have been revealed. In ZnO crystals, the microhardness increases, whereas in TGS and KAP, it decreases. A maximum change (10–15%) is reached within 1–3 h after magnetic treatment; then, the microhardness gradually recovers to its initial value for the first day. After a sufficient pause, the effect is completely reproduced under the same conditions. The resonant frequency of the pump field $$\tilde B$$ corresponds to the EPR condition with a g-factor close to two. The magnetic memory exhibits a strong anisotropy: for each of the crystals, a direction is found, which, being coincident with the Earth’s magnetic field vector B Earth, causes complete or partial suppression of the effect. In ZnO and TGS crystals, these are symmetry axes 6 and 2, respectively. In the KAP crystal, it is the direction in the cleavage plane orthogonal the 2 axis. Possible physical mechanisms of the observed phenomena have been discussed.

Alshits V.I., Darinskaya E.V., Morozov V.A., Kats V.M., Lukin A.A.

Three resonant peaks l(ν) of dislocation paths, appearing in NaCl crystals under simultaneous exposure to the Earth’s magnetic field B Earth and an ac pump field $$\tilde B$$ have been observed in the radio-frequency range (ν ∼ 1 MHz). Each peak corresponds to a specific experimental geometry. Resonance frequencies correspond to ordinary EPR conditions in which, however, instead of the total Earth’s field, its projections onto particular crystallographic directions play part. These directions are probably related to orientations of magnetic moments at impurity centers in dislocation cores. A physical model describing well the positions all three EPR peaks l(ν) is proposed. The peak height l m is proportional to the squared amplitude of the pump field and the time t of sample exposure to crossed fields: $$l_m \propto \tilde B_m^2 t$$ . The threshold amplitude $$\tilde B_m^{th} \sim 1 \mu {\rm T}$$ of the pump field is detected, below which the effect rapidly disappears. The time of spin-lattice relaxation of radical pairs on dislocations is estimated by the threshold field $$\tilde B_m^{th}$$ level.

Alshits V.I., Darinskaya E.V., Morozov V.A., Kats V.M., Lukin A.A.

The resonance displacements of the dislocations, l ∼ 100 μm, in NaCl crystals placed in the crossed Earth’s magnetic field B Earth and the ac field % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaceWGcb % GbaGaaaaa!3878! $$ \tilde B $$ ≈ 3 μT of the variable frequency ν ∼ 106 Hz have been discovered in the absence of any other impact on the crystals. Two peaks of the mean dislocation path l(ν) with the maxima at ν1 = 1.3 MHz and ν2 = 3 MHz have been observed for the field % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0x % c9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8fr % Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaieqace % WFcbGbaGaaaaa!387E! $$ \tilde B $$ oriented along the vertical and horizontal components of B Earth, respectively. The effect is explained by the depinning of the dislocations from the impurity centers after their structural transformation due to the ESR in the dislocation-impurity system in the crossed fields. The subsequent motion of the dislocations proceeds under the action of internal stress in the crystals. A physical model has been proposed to explain the strong anisotropy of the effect with respect to the mutual orientation of the dislocation lines and magnetic fields.

Alshits V.I., Darinskaya E.V., Koldaeva M.V., Petrzhik E.A.

Buchachenko A.L.

The magnetoplastic effect in mechanics of nonmagnetic crystals is attributed to spin evolution in the spin-selective nanoscale reactor created by electron transfer from a dislocation to a stopper. In this “dislocation + stopper” system, dislocation depinning is facilitated because the Coulomb attraction between the dislocation and the stopper is switched off. Since magnetic field stimulates the singlet-to-triplet conversion of the nanoscale reactor (the reverse electron transfer is forbidden), the nanoscale reactor with switched-off Coulomb interaction has a longer lifetime. The resulting increase in depinning rate and dislocation mobility provides a physical explanation for magnetoplasticity.

Badylevich M.V., Kveder V.V., Orlov V.I., Ossipyan Y.A.

In this work we have observed a significant increase of unlocking stress for dislocations in Cz-Si caused by the microwave magnetic field in a condition of spin resonance corresponding to g-factor value of about 2.0. The result can be interpreted in terms of spin-dependent reactions of oxygen accumulated at dislocations. However, the specific atomistic model for the effect is still missing. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Koldaeva M.V., Alshits V.I.

Dislocation motions are studied in NaCl crystals exposed to an EPR impact under crossed ultralow magnetic fields, the Earth field BEarth ∼ 50 µT, and the AC pumping field B̃(ν) of the amplitude 2.5 µT in the frequency band of 6 kHz to 2.1 MHz. Mean dislocation paths form a spectrum of multiple peaks at definite resonance frequencies. Dislocation motions are supposed to be caused by spin-dependent transformation of impurity centers, which, in turn, provide depinning of dislocations and relaxation of their structure. The observed spectrum is attributed to specific features of the hyperfine EPR at the applied field BEarth small as compared with the crystalline local fields Bloc created by nuclei of Cl ligands surrounding the Ca pinning centers. The developed theory well describes peak positions in the observed frequency spectrum.

Buchachenko A.L.

Kraiev M., Voronkov E., Kraieva V.

PurposeThe purpose is to calculate the change in the total energy of a small fragment of an idealized lattice of iron (in its pure form and with impurity atoms) containing an edge dislocation during its elementary motion at one interatomic spacing, both under the influence of a constant magnetic field and without it. The introduction of a magnetic field into the system is aimed at checking the adequacy of the description of the phenomenon of magnetoplasticity by changing the total energy of the atomic system.Design/methodology/approachThe design procedure is based on a quantum-mechanical description of the switching process of the covalent bond of atoms in the dislocation core. The authors used the method of density functional theory in the Kohn-Shem version, implemented in the GAUSSIAN 09 software package. Using the perturbation theory, the authors modeled the impact of an external constant magnetic field on the energy of a system of lattice atoms.FindingsThe simulation results confirmed the effect of an external constant magnetic field on the switching energy of the covalent bond of atoms in the dislocation core, and also a change in the magnetic susceptibility of a system of atoms with a dislocation. This complements the description of the magnetoplastic effect during the deformation of metals.Originality/valueThe authors created quantum-mechanical models of the dislocation motion in the Fe crystal lattice: without impurities, with a substitutional atom Cr and with an interstitial atom C. The models take into account the influence of an external constant magnetic field.

Petrzhik E.A., Alshits V.I.

A resonance decrease in the microhardness of Ni-doped NaCl crystals exposed in the EPR scheme to ultralow mutually perpendicular magnetic fields including the Earth’s static magnetic field $${{B}_{{{\text{Earth}}}}} \approx 50$$ μT and an alternating field with an amplitude of about 3 μT at frequencies 1.1–2.2 MHz is discovered. A series of softening peaks separating into two groups each consisting of nine peaks are identified. Resonant frequencies in the groups are related by the empirical relationship $$\nu _{n}^{{{\text{II}}}} \approx \nu _{n}^{{\text{I}}}{\text{/}}\sqrt 2 $$ ( $$n = 1,\;...,\;9$$ ). The maximum decrease in the microhardness is observed 2–3 h after exposure, and then it slowly relaxes to its initial value. The interpretation of the observed effects, including the relation between the frequencies $$\nu _{n}^{{\text{I}}}$$ and $$\nu _{n}^{{{\text{II}}}}$$ , is based on the features of resonance magnetoplasticity, when the external field ( $${{B}_{{{\text{Earth}}}}}$$ ) is several orders of magnitude lower than the local magnetic fields in the crystal.

Shpeizman V.V.

Deformation rates of lead under uniaxial compression at constant stress and temperature, as well as characteristics of deformation rate jumps in the initial period of constant magnetic field action and immediately after its termination, have been determined. It is established that, under these conditions, a sharp change in the deformation rate is followed by its short-term return characterized by increased spread of the deformation rate related to its jumps and increased interval of nanometer-scale deformation jumps.

Galustashvili M.V., Driaev D.G., Kvatchadze V.G.

The effect of a weak magnetic field on stress relaxation in NaCl crystals after the termination of active deformation has been experimentally studied for the first time. The results indicate that stress relaxation is accompanied by the magnetoplastic effect in the form of an increase in the relaxation depth and significant softening, sensitive to the active deformation rate. These effects are strongly enhanced when a magnetic field is combined with a weak electric one.

Darinskaya E.V., Koldaeva M.V., Alshits V.I., Pritula I.M., Voloshin A.E.

The dependence of the microhardness of KDP crystals with embedded TiO2 nanoparticles on the time passed after their exposure to a dc magnetic field has been analyzed. Samples cut from different growth sectors are found to be differently affected by magnetic treatment. In the absence of TiO2 impurity, the microhardness of the samples from the {100} growth sector decreases after the magnetic exposure, whereas the microhardness of the samples cut from the {101} growth sector changes in two stages (hardening after softening). With an increase in the TiO2 concentration, the softening stage gradually disappears in the crystals from both growth sectors. In the KDP:TiO2 crystals from the {100} sector, hardening (which was absent previously) occurs instead of softening. In the crystals from the {101} sector, the hardening arises after a shorter time.

Buchachenko A.L.

Микроволновое облучение преобразует упругость твёрдых тел в пластичность, управляя подвижностью дислокаций через магнитные взаимодействия в электронно-спиновых парах на дислокациях. В ионных кристаллах микроволны производят увеличение скорости движения дислокаций и длины их пробега, обеспечивая высвобождение упругой энергии; в ковалентных кристаллах они закрепляют дислокации, аккумулируя упругую энергию и увеличивая прочность кристаллов. Эффекты микроволновой накачки на резонансных зеемановских частотах (в режиме магнитных резонансов) являются твёрдым доказательством физики электронно-спиновых пар и самого явления магнитопластичности. Однако главный вклад в макроскопическое преобразование упругой энергии в пластическое течение вносят нерезонансные поля. Именно их можно использовать для управления механикой диамагнитных твёрдых тел, включая очаг землетрясения. Наблюдаемые корреляции между магнитными событиями (магнитные бури, мощные магнитные импульсы магнитогидродинамических генераторов) и их сейсмотектоническими следствиями (частота и амплитуда землетрясений и деформаций) указывают на то, что магнитный контроль очага землетрясений реален и может использоваться для предотвращения катастроф и преобразования крупномагнитудных землетрясений в слабые, маломагнитудные.

Guillon O., Elsässer C., Gutfleisch O., Janek J., Korte-Kerzel S., Raabe D., Volkert C.A.

The use of external electric and magnetic fields for the synthesis and processing of inorganic materials such as metals and ceramics has seen renewed interest in recent years. Electromagnetic energy can be utilized in different ways to improve or accelerate phase formation and stabilization, chemical ordering, densification and coarsening of particle-based materials (pore elimination and grain growth), and mechanical deformation (plasticity and creep). In these new synthesis and processing routes, the resulting microstructures and macroscopic material behavior are determined by the interaction of the applied fields with defects such as single or clustered point defects, dislocation networks, and interfaces. Multiscale experimental investigations and modeling are necessary to unveil the mechanisms underlying this field-assisted manipulation of matter.

Alshits V.I., Koldaeva M.V., Petrzhik E.A.

It is shown that the preliminary exposure of ZnO, triglycine sulfate, and potassium hydrogen phthalate crystals in ultralow crossed magnetic fields—Earth’s magnetic field and ac pump field—leads to a resonance change in their microhardness. The resonance frequency of microhardness peaks is determined by the classical condition of electron paramagnetic resonance only at certain orientations of the crystals with respect to the Earth’s magnetic field BEarth. Rotations of all samples with respect to the direction BEarth by angle θ reduce the resonance frequency in proportion to cosθ. The observed anisotropy has been attributed to the presence of their own local magnetic fields Bloc ≫ BEarth in the crystals.

Volchkov I.S., Kanevskii V.M., Pavlyuk M.D.

The effect of static and pulsed magnetic fields (~1 T) on the electrical conductivity of CdTe crystals has been revealed. With a delay after the magnetic exposure of crystals, the effect is observed in the form of two peaks of their conductivity with the subsequent relaxation return. The first peak at both types of magnetic treatment is observed ~1 h after exposure and its amplitude exceeds the background value by ~23–36% (the larger value corresponds to the static field). The second peak appears in both cases also at commensurate but much larger delays of ~50–60 h, and its amplitudes are much different for the two types of exposure, exceeding the background by ~60% for the static field and only by ~11% for the pulsed field. Possible mechanisms of the observed effects have been discussed.

Driaev D., Iashvili A., Kankadze L., Tsakadze S.

Apparatus for measurements of internal friction from Q−1∼10−6 and elastic moduli in the kilohertz frequency range in which external friction losses were minimized using a new-type of three-reed tuning fork as a sample under study is described. High sensitivity of the apparatus made it possible to observe a resonance plasticization of diamagnetic LiF crystals under the action of crossed magnetic fields (≈100 μT) in the EPR conditions.