196,153 research outputs found
Magnetocrystalline anisotropy of the 3d sublattice in the cubic intermetallic system Zr6Co23-xMx (M= Fe, Ni)
No full textThe magnetocrystalline anisotropy behavior of the 3d sublattice was studied in the face‐centered‐cubic system Zr6Co23−xMx (M=Fe,Ni). A remarkably high anisotropy field was required to saturate the magnetization along both the [100] and [110] hard directions. The values found are, respectively, HA=43 kOe and HA=33 kOe at 293 K for Zr6Co23. The partial substitution of Co with Ni results in a substantial increase of the anisotropy while saturation magnetization and Curie temperature decrease linearly. On the contrary, the partial substitution with Fe gives rise to a decrease of HA and to an increase of both σs and Tc. The 10th power law does not apply to the functional temperature dependence of the resulting anisotropy in this system
On the direct measurement of the adiabatic temperature change of magnetocaloric materials
No full textThe direct measurement of the adiabatic temperature change of magnetocaloric materials is
fundamental to design efficient and eco-friendly magneto cooling devices. This work reports an
overview of the measurement principle and of the main experimental issues that have to be
considered to obtain a reliable characterization of materials. The effect of non-ideal adiabatic
conditions, the role of the temperature sensor and the influence of specific properties of the
material are discussed on the basis of finite-difference thermal simulations and special designed
experiments. Two cases are considered in detail: the characterization of thin samples and the
measurement of caloric response to fast field changes. Finally, the impact of different
measurement protocols is discussed in the case of materials with first-order transitions
Energy Transfer Mechanism in the NaCl:Pb++,Mn++ System along Aggregation Processes
No full textThe non-radiative energy transfer mechanisms between Pb++ (donor) and Mn++ (acceptor) ions in NaCl:Pb++, Mn++ system are examined at different aggregation stages of the impurities. Mn++ ions are characterized by a series of absorption bands partially overlapping the emission bands of Pb++ aggregates peaking at 380, 430, and 500 to 530 nm. The energy transfer mechanism connected with Pb++-380 nm emission band is based on a resonant single pair interaction, while the transfer process connected with 430 nm and 500 to 530 nm emission bands can be explained on the basis of a fast energy migration within the donor system followed by a final transfer, donor–acceptor, that is resonant for the transfer connected with 430 nm band and phonon assisted for the transfer connected with the 500 to 530 nm band
Magnetocaloric characterization of materials
No full textThe magnetocaloric effect manifests itself as a change in temperature of a magnetic material following the variation of an applied magnetic field. This effect constitutes the basis for the development of important applications such as magnetic refrigeration and, in general, thermomagnetic energy conversion technologies. Accurate and reliable characterization of the magnetocaloric effect is crucial for identifying and selecting the most promising materials and for realistic design of refrigerant machines. This chapter provides a comprehensive and critical review of the methods and experimental setups developed for measuring the magnetocaloric effect. It offers an in-depth discussion and analysis of both indirect magnetometric and calorimetric methods and direct methods, along with detailed descriptions of the experimental setups adopted. Each technique is examined to highlight its primary advantages and potential issues, providing a practical guide for obtaining accurate magnetocaloric characterizations of materials. The chapter also addresses the measurement of the effect across first-order transitions, emphasizing the importance of proper measurement protocols. Special conditions, such as rapid field changes or low-mass samples, are considered carefully, as they can provide new insights into material properties or simulate real application conditions. Additionally, some recent advanced experimental techniques are presented, which are capable of simultaneously measuring different physical properties of materials or coupled multicaloric effects
Proton-conduction under mild humid conditions in [NH4][M(HCOO)3] (M=Mn2+, Co2+) frameworks
No full textRoom temperature proton conduction was investigated in ammonium-based formate frameworks [NH4][M(HCOO)3] (M = Mn2+, Co2+) well-known for their ferroelectric and magnetic properties at low temperature. The synthesis was achieved through mechanosynthesis and proton conduction measurements were performed in ambient as well as in humidity and temperature controlled conditions. The proton conduction is activated by reaching the relative humidity (RH) limit of 50 % for both compounds. At 294 K a maximal conductivity of 2.2 ± 0.3 × 10−4 S/cm is observed for [NH4][Mn(HCOO)3] under RH = 70 %. The lack of proton conduction behavior in the isostructural compound Cs [Mn(HCOO)3] corroborates the role played by the NH4+ units as proton vehicle
Chapter 9: "Ac susceptibility studies on magnetic materials"
No full textIn the present chapter a concise review concerning the AC susceptibility technique applied to bulk magnetic compounds, and thin films is presented. The measurement of the
dynamical properties of magnetic compounds has become extremely important in the understanding of complex magnetic phenomena such as spin glass and spin glass like
transitions; moreover the employment of very low magnetic fields allows to better analyze these phenomena with no consistent modifications of the original magnetic structure. After a brief introduction in the first paragraph outlining the importance of the AC susceptibility in the analysis of the magnetic behavior of complex compounds, a few details about the theory and the measurement apparatus are reported respectively in sections 2 and 3. In section 4 a selection of representative linear and non linear AC susceptibility measurements are reported performed either as a function of temperature either as a function of a bias applied DC field
Alternating field gradient susceptometer
No full textA new type of high sensitivity susceptometer has been developed. It is based on the principle of alternating field gradient, using a thin metallic wire as a resonating system. Test measurements up to 750°C have been performed on samples with a mass of few μg, like Ni foils, Fe-Al multilayers, Ba-ferrite disks and single crystals of ZnCo-W Ba-ferrite
Singular point detection of energy losses in hard magnetic materials
No full textThe real and the imaginary part of the reversible parallel susceptibility (RPS) and it harmonics was measured using the modulation technique. Singular Point Detection (SPD) peak in the second harmonic of the complex susceptibility was observed
Mechanosynthesis of multiferroic hybrid organic-inorganic [NH4][M(HCOO)3] M = Co2+,Mn2+,Zn2+,Ni2+, Cu2+ formate-based frameworks
No full textThe family of compounds with formula [NH4][M(HCOO)3], with M a divalent D-metal, is characterized by porous frameworks hosting NH4+ cations exhibiting at low temperature a spontaneous ferroelectric polarization. The presence of magnetically active divalent metal determines the occurrence of antiferromagnetic ordering below 30 K opening the avenue for a rational formulation of a new class of multiferroic materials. We demonstrate that this intriguing class of compounds can be synthetized with a mechanochemical approach. This novel route of synthesis was applied to the series [NH4][M(HCOO)3] with M= Cu2+, Co2+, Mn2+, Zn2+ and Ni2+ using as reactants ammonium formate and the corresponding di-hydrated metal formates. The milling duration of the process correlates with the thermal stability of the di-hydrated metal formates indicating that the first step of the mechanosynthesis process is represented by the removal of water molecules. The characterizations of the final products indicate the presence of single phase [NH4][M(HCOO)3] compounds with an excellent degree of crystallinity
- …
