Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition

The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with coupled magnetic and structural (martensitic) phase transitions were studied experimentally and theoretically. The magnetocaloric effect was measured by a direct method in magnetic fields 0-26 kOe at temperatures close to the magnetostructural transition temperature. For theoretical description of the alloy properties near the magnetostructural transition a statistical model is suggested, that takes into account the coexistence of martensite and austenite domains in the vicinity of martensite transformation point.Comment: presented at ICM-2003, to appear in JMM

Experimental investigation of magnetic circular dichroism spectrum and stress induced optical activity in a single-defect photonic crystal

Experimental investigation results for the magnetic circular dichroism spectrum (MCD) of a photonic crystal (PC) are presented. We found that in the vicinity of the transmission peak within the photonic bandgap and also near the bandgap edges, the circular dichroism is measurable even in the absence of any applied magnetic field. The application of magnetic field leads to generating an additional MCD signal measurable at the wavelengths near the “defect mode” transmittance line

Technological challenges of 1-dimensional magnetic photonic crystals

Visible-region magnetic photonic crystals (MPC) designed for higher-order bandgap operation have been proposed to overcome the technological restrictions originating from the strong thickness dependency of the individual magnetic layer properties observed in MPC structures

Electromagnetic Waves Absorption by Graphene-Magnetic Semiconductor Multilayered Nanostructure in External Magnetic Field: Voight Geometry

Absorption of electromagnetic waves by graphene-magnetic semiconductor multilayered structure has been investigated for the Voight geometry with taking into account the dissipation processes. The possibility of control of electrodynamic properties of the structure by an external magnetic field, changing in number of periods of the structure, chemical potential of the graphene layers and temperature has been shown. Electrodynamics of the structure is also sensitive to polarization of the incident wave. The structure shows to be especially controllable at terahertz frequencies

Electromagnetic Waves Generation in Ni2.14Mn0.81GaFe0.05Ni_{2.14}Mn_{0.81}GaFe_{0.05} Heusler Alloy at Structural Phase Transition

Electromagnetic waves generated by the Heusler alloy $Ni_{2.14}Mn_{0.81}GaFe_{0.05}$ at structural phase transition was detected in the frequency range of 28-32 GHz. Influence of the kinetics of phase transitions on the nature of the sample millimeter radiation was studied as well. It has been observed that the contribution of the intrinsic radiation increases with increasing of the heating/cooling rate. The possible mechanisms and theory of such effect is discussed. It is shown that the maximum radiation intensity should be emitted in direction perpendicular to the movement of interphase boundary

Martensitic and inter-martensitic transformations in magnetocaloric Ni2.15Mn0.85Ga Heusler alloy

The entropy changes of successive martensitic phase transformations in Ni-Mn-Ga Heusler alloys can be utilized to realize enhanced magnetocaloric properties. A detailed study of phase transformations of one such alloy, Ni2.15Mn0.85Ga, (ΔQ = 4900 J/kg at 343 K, under 140 kOe), is reported here. Upon cooling, the paramagnetic cubic (L21) austenitic phase transforms into a ferromagnetic 7M modulated monoclinic martensitic phase. This phase is stable in a narrow temperature range, and upon further cooling, transforms into a non-modulated ferromagnetic tetragonal (L10) phase. The separation between the equilibrium temperatures of the austenitic and tetragonal martensitic phases is only ~50 K. The alloy undergoes reversible temperature-induced martensitic and inter-martensitic phase transformations with thermal hysteresis of about 25 K. The conclusions from the detailed study of the phase transformations lead to new possibilities to enhance the magnetocaloric effect by utilizing the entropy associated with multi-structural transformations