F. B. Mushenok

Thermally-induced paramagnetism of spiropyrane iodides

Thermally stimulated paramagnetism has been found in the iodides of organic spiropyrane molecules, namely 1-isopropyl-3,3,5′,6′-tetramethylspiro(indolino-2,2′-[2H]pyrano[3,2-b]pyridinium) (SpSpSp) and spiro(1,3,3,7′-tetramethyl-indolino-2,3′-3H-pyrano[3,2-f]quinolinium) (Sp2Sp2). The activation energy of their triplet states was determined from the temperature dependence of their magnetic moments: 0.023 and 0.032 eV, respectively. It was found that the magnetic moment, μeff, increases under UV light (250–400 nm) due to the formation of high-spin (S = 3) states of the molecules.

(S)-(−)-(2-MeBu)N(Pr)2MeI Salt as Template in the Enantioselective Synthesis of the Enantiopure Two-dimensional (S)-(−)-(2-MeBu)N(Pr)2Me[ΛMnΔCr(C2O4)3] Ferromagnet

We describe herein the synthesis of (rac)- or enantiopure (S)-(-)-(2-MeBu)N(Pr)₂MeI ammonium salts. These racemic and enantiopure ammonium salts were used as cationic templates to obtain new two-dimensional (2D) ferromagnets [(rac)-(2-MeBu)N(Pr)₂Me][MnCr(C₂O₄)₃] and [(S)-(-)-(2-MeBu)N(Pr)₂Me][ΔMnΛ nCr(C₂O₄)₃]. The absolute configuration of the hexacoordinated Cr(III) metallic ion in the enantiopure 2D network was determined by a circular dichroism measurement. The structure of [(2-MeBu)N(Pr)₂Me][MnCr(C₂O₄)₃], established by single crystal X-ray diffraction, belongs to the chiral P63 space group. According to direct current (dc) magnetic measurements, these compounds are ferrromagnets with a temperature Tc = 6°K.

Ferromagnetic resonance in the Cr1/3NbS2 helical magnet

The high-frequency spin excitations in the Cr1/3NbS2 helical magnet have been investigated. The contributions of the uniform and Goldstone modes of the spin precession have been determined. It has been shown that the resonant field of the uniform mode is determined by the uniaxial magnetocrystalline anisotropy. Final values of the energy and the resonant field of the Goldstone mode are determined by the sixth-order magnetocrystalline anisotropy in the basal plane.

Effect of dehydration on the ferrimagnetic resonance in [Cr(CN)6][Mn(S)-pnH(H2O)](H2O) single crystals

The effect of dehydration-induced structural transitions on the ferrimagnetic resonance spectra of the [Cr(CN)6][Mn(S)-pnH(H2O)](H2O) chiral molecular magnet has been studied for three crystalline modifications. The differences in the anisotropy field and exchange interaction constants due to the change in the dimensionality of the magnetic ordering upon the phase transitions have been established. In the dehydrated amorphous phase, apart from the ferrimagnetic resonance, additional isotropic magnetic resonance lines corresponding to the spin-glass state have been revealed.

Synthesis, structure, and properties of a new representative of the family of calix[4]arene-containing [MnII2MnIII2]-clusters

A new representative of calix[4]arene-containing tetranuclear manganese complexes of the [MnII2MnIII2] type was obtained. According to the data of magnetoochemical studies, the complex exhibits properties of molecular magnet at the temperature below 5 K. Parameters of the exchange interaction and the activation energy were determined. The influence of the peripheral environment on the magnetic properties of the tetranuclear manganese framework in the structure of the complex was revealed.

Magnetic properties of single crystals based on photochromic molecules of spiropyrans and chromium oxalates

The influence of UV irradiation on the effective magnetic moment and the Weiss temperature of single crystals based on photochromic molecules of spiropyrans and chromium oxalates is revealed. It is demonstrated that the irradiation of the samples leads to the appearance of an additional EPR line in high magnetic fields H = 15.3 kOe. The analysis of the angular dependences of the EPR spectra makes it possible to determine the contribution of Cr3+ ions to the magnetic properties. The crystal field parameters determined from the experimental data indicate that the field of the ligands surrounding the Cr3+ ions has an axial symmetry. The Weiss constants for the powdered sample before irradiation (25 K) and after irradiation (−25 K) are obtained and analyzed. It is shown that the deviation of the temperature dependence of the magnetic moment from the Curie law is associated with the redistribution of electrons between the Cr3+ and Cr4+ ions rather than with the exchange interaction.

Ordered nanowires of photochromic compounds based on spiropyrane and transition metal complexes

Ordered nanowires of photochromic antiferromagnet SpFeMn(C2O4)3 (Sp is 1-{1′,3′,3′-trime-thyl-6-nitro-5′-chlorspiro[2H-1-benzopyran-2,2′-indolin]-8-yl)methyl}pyridinium) are synthesized in anodized aluminum oxide (AAO) pores 20 nm and 200 nm in diameter. A change in the magnetic properties of the material due to its nanostructuring is observed, resulting in the suppression of canted spin ordering (spincanted phase) in favor of the uniaxial antiferromagnet phase.

Influence of chirality on the electron spin resonance in molecular magnets [MnII(HL)(H2O)][MnIII(CN)6] · 2H2O with chiral ligands L

Chiral and racemic molecular ferrimagnets [MnII(HL)(H2O)][MnIII(CN)6] · 2H2O, where L = S-or R-1,2-diaminopropane for chiral samples (S-pn, R-pn) and L = rac-pn for racemic samples, are investigated by the electron spin resonance technique. It is revealed that the electron spin resonance spectra of the chiral and racemic samples differ from each other at temperatures below the Curie temperature TC = 21 K. The maximum in the temperature dependence of the integrated magnetic susceptibility χ(T) calculated by the double integration of the line centered at a negative field of −250 Oe for the racemic samples is broadened as compared to the maxima in the corresponding dependences for the enantiomers of the chiral samples with “right” (R) and “left” (S) symmetry. The new compounds under investigation differ from the previously synthesized crystals by the strong spin-orbit interaction between Mn3+ ions, which leads to a dependence of their magnetic properties on the chirality of the structure.

Bolometer detection of magnetic resonances in nanoscaled objects

We report on a nanoscaled thermocouple (ThC) as a temperature sensor of a highly sensitive bolometer for probing the dissipative damping of spin dynamics in nanosized Permalloy (Py) stripes. The Au-Pd ThC based device is fabricated by standard electron beam lithography on a 200 nm silicon nitride membrane to minimize heat dissipation through the substrate. We show that this thermal sensor allows not only measurements of the temperature change on the order of a few mK due to the uniform resonant microwave (MW) absorption by the Py stripe but also detection of standing spin waves of different mode numbers. Using a 3D finite element method, we estimate the absorbed MW power by the stripe in resonance and prove the necessity of using substrates with an extremely low heat dissipation like a silicon nitride membrane for successful thermal detection. The voltage responsivity and the noise equivalent power for the ThC-based bolometer are equal to 15 V W(-1) and 3 nW Hz(-1/2), respectively. The ThC device offers a magnetic resonance response of 1 nV/(μ(B) W) corresponding to a sensitivity of 10(9) spins and a temperature resolution of 300 μK under vacuum conditions.

Photomagnetic effect in molecular magnets based on nitrosyl complexes of ruthenium and rare-earth ions

The magnetic properties of new bifunctional molecular magnets based on nitrosyl complexes of ruthenium and thiacalix[4]arenes of rare-earth ions (Gd3+, Dy3+) have been investigated. A photoinduced decrease in the magnetization of the molecular magnet with rare-earth ions Gd3+ and the absence of a photomagnetic effect in crystals with rare-earth ions Dy3+ have been revealed at a temperature of 2 K. It has been found that, in the sample containing Dy3+ ions, the magnetization deviates by 6% from the calculated value for noninteracting ions. A comparison of the results obtained for two groups of isostructural samples, which differ only in the type of rare-earth ions, has demonstrated that the observed deviation of the magnetization is caused by the interaction of the orbital moment of the Dy3+ ions with the crystal field.