Effect of a pulsed magnetic field on the microhardness of C60 single crystals

Magnetic-field pulses with induction greater than 10 T were observed to influence the microhardness of C₆₀ single crystals. It was established that the magnetic field reversibly alters the bulk properties of the material. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 110–113 (25 January 1999)     

Effect of magnetic field on the microplastic strain rate for C60 single crystals

Microplastic deformation in a magnetic field and in a zero field, as well as after preliminary action of a magnetic field on C₆₀ crystals, is studied with the help of a laser interferometer, which makes it possible to measure the strain rate on the basis of linear displacements of 0.15 µm. It is shown that the introduction of a sample into the field and its removal from a field of 0.2 T directly during sample deformation lead to a change in the strain rate, the decrease in the rate being accompanied by a brief interruption of deformation. The sign of the effect depends on temperature: the magnetic field accelerates deformation at room temperature and slows it down at 100 K. Preliminary holding of a sample in a field of 0.2 or 2 T produces a similar effect on the strain rate. Possible reasons for the observed manifestations of the magnetoplastic effect in C₆₀ and the relation between the sign of the effect and the phase transition at 260 K are considered.     

Influence of a weak magnetic field on microplasticity of silicon crystals

The possibility of magnetic ordering at dangling bonds in dislocation cores has been investigated theoretically. It has been experimentally shown that magnetic ordering in dislocations affects the spin-dependent effects occurring in dislocation crystals of silicon. It has been found that preliminary magnetic treatment of silicon crystals in a weak magnetic field leads to the suppression of the electroplastic effect induced in silicon crystals excited by an electric current. It has been assumed that a change in the microplasticity under the combined action of a magnetic field and an electric current is caused by a weakening of spin-dependent recombination at dislocation dangling bonds.     

Thermal conductivity of C60 and C70 crystals

We have performed thermal conductivity measurements on C₆₀ and C₇₀ crystals grown by sublimation. For single crystal C₆₀, the thermal conductivity k is 0.4 W/m K at room temperature and is nearly temperature independent down to 260K. We observed a sharp orientational phase transition at 260K, indicated by a 25% jump in k. Below 90K, k is time dependent, which manifests itself as a shoulder-like structure at 85K. The temperature and time dependence of k below 260K can be described by a simple model which accounts for the thermally activated hopping of C₆₀ molecules between two nearly degenerate orientations, separated by an energy barrier of 240 meV. It is found that solvents have a strong influence on the physical properties of C₇₀ crystals. For solvent-free C₇₀ crystal, k is about constant above 300K. There is a broad first-order phase transition in k at 300K with a 25% jump. We associate this transition with the aligning of the fivefold axes of the C₇₀ molecules along the c-axis of the hexagonal lattice. Upon further cooling, k increases and is time independent.     

The influence of a magnetic field on the inelastic properties of LiF crystals

The effect of weak magnetic fields (0.1–0.8 T) on the internal friction and Young’s-modulus defect of LiF crystals is investigated over a range of relative strain amplitudes ɛ ₀ from 10⁻⁶ to 10⁻⁴ at frequencies of 40 and 80 kHz. Experiments with these fields show that the internal friction increases and the effective elastic modulus decreases, indicating an increase in the plasticity of the samples. Plots are obtained of the internal friction versus the magnitude of the magnetic field at various values of the strain amplitude ɛ ₀. Fiz. Tverd. Tela (St. Petersburg) 41, 1035–1040 (June 1999)     

磁场对La2－xSrxCuO4单晶热导的影响研究

报道了系列欠掺杂La_2-xSr_xCuO₄（x=0063,0070,0 090,0110,0125）单晶的零场和加磁场情况下ab面和c方向的热导率与温度的关系曲线，测量 温度范围从2到45K. 研究发现ab面和c方向的热导率都受到磁场的压制. 而且在磁场 的作用下，热导压制率随温度变化的关系和场致反铁磁有序的增强与温度的依赖关系有高度 相似性. 认为磁场引起的ab面的热导压制主要是电子热导的变化所致，而c方向的 压制则可能主要来源于声子热导的变化，它们均可能与磁场诱导下欠掺杂La_2-x Sr_xCuO₄的某种电荷有序和磁有序的增强密切相关. 关键词： 热导 电荷有序 磁有序     

Selective effect of a weak DC magnetic field on triglycine sulfate crystals

The effect of the selective influence of a dc magnetic field on the characteristics of nominally pure triglycine sulfate crystals was detected for the first time. A short (minutes) exposure to a weak magnetic field B₀=0.08±0.01 T caused long-term (hundreds of hours) changes in the spontaneous polarization, coercive field, Curie temperature, and permittivity of the crystal at the Curie point. The effect is selective in nature presumably because of the participation of hydrogen bond protons in the spin-dependent processes of the transformation of defect complexes in real crystals.     

IR photoconductivity of C60 fullerene single crystals

The photoconductivity in the range 0.3–0.9 eV was investigated in a high-quality C₆₀ fullerene single crystal. It was concluded that the crystal investigated is an extrinsic semiconductor. Fiz. Tverd. Tela (St. Petersburg) 41, 1113–1114 (June 1999)     

The influence of low doses of β irradiation on the conductivity of C<Subscript>60</Subscript> single crystals

The electrical conductivity of C₆₀ single crystals is found to increase by 55–120% under β irradiation with low doses. It is shown that this effect can be associated with multistage collision ionization of C₆₀ molecules.     

On the influence of a weak magnetic field on the drift motion of charged particles

The results obtained in [1] are generalized to the case when an arbitrarily oriented magnetic field is present by allowance for the influence of a magnetic field with cyclotron frequency less than the collision frequency on the dependence of the drift velocity on the velocity of random motion (Langevin equation). A study is made of the influence of a magnetic field on the equation of drift motion derived in [1] and this field is allowed for in the previously obtained results of the solution of that equation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 69–72, May, 1972.     

Effect of a constant magnetic field on the photoconductivity of single-crystal C60

Magnetic fields with induction B<1 T are found to affect the photocurrent in single-crystal C₆₀. This effect does not reduce to the Hall effect. The effect of the field on the multiplicity of short-lived pairs consisting of mobile carriers and their traps is proposed as a possible explanation for the observed phenomenon. Fiz. Tverd. Tela (St. Petersburg) 41, 2097–2099 (November 1999)     

On the influence of a constant magnetic field on the electroplastic effect in silicon crystals

The influence of a constant magnetic field on the electroplastic effect induced by an electric current in silicon crystals is investigated. It is found that the preliminary magnetic field treatment of silicon crystals leads to a weakening of the electroplastic effect. A possible mechanism of the phenomena observed is discussed.     

Effect of a magnetic field on the flow stress of Co and Fe single crystals

In a range of plastic deformation, the flow stress drop and the stress relaxation of Co and Fe single crystals are observed under an a.c. magnetic field. The magnitude of these drops is discussed on the basis of different deformation modes due to the crystal structure.     

Effect of a magnetic field on the plasticity and photo-and electroluminescence of ZnS single crystals

It is found that a ∼10 T magnetic field influences the microhardness and the photo-and electroluminescence of ZnS single crystals containing microtwins. It is established that a magnetic field irreversibly changes the properties of the crystal, leading to relaxation of the metastable states of structural defects. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 114–118 (25 January 1999)