Properties Of Low-temperature Phase Research Articles

Studies on preparation and properties of low temperature phase of MnBi prepared by electrodeposition

MnBi alloy with low-temperature phase (LTP) is a promising candidate as rare-earth-free permanent magnet for its high intrinsic coercivity and the unique positive temperature coefficient. Many works have investigated on the preparation of the LTP-MnBi using physical methods, while there are few reports about the successful fabrication using electrodeposition method although this low cost process has been used for many material preparations so far. The main difficulty is the large negative reduction potential of manganese ions and on the basis the big difference between the reduction potentials of manganese ions and bismuth ions. In this paper, we reduced the reduction potentials of manganese ions and bismuth ions firstly and on this basis, the MnBi films with different ratios of manganese and bismuth were prepared using different deposited potentials. After annealed treatment of 380 °C, there appears the low temperature phase in XRD pattern for the sample in which the ratio of manganese and bismuth is 54:46. This is the first report in electrodeposited method so far and the corresponding coercivity reaches 1450 Oe measured by the physical property measurement system (PPMS).

INS, DFT and temperature dependent IR investigations of dynamical properties of low temperature phase of choline chloride

Within the framework of the research the inelastic neutron scattering and temperature dependent infra-red spectroscopy investigations of the low temperature phase of choline chloride were performed. The infra-red spectra in wavenumber region 4000–80cm−1 and in a temperature range 9–300K were collected. The density functional theory calculations with the periodic boundary conditions for determination and description of the normal modes in the vibration spectra of choline chloride were applied. Bands assigned to the CH3 torsional vibration were observed at 288 and 249cm−1. From the analysis of the temperature dependence of the full-width-at-half-maximum the activation energy for CH3 group reorientation is found to be equal to 1.6±0.2kcal/mol.

MnBi particles with high energy density made by spark erosion

We report on the properties of low-temperature phase (LTP)-MnBi particles produced by the rapid-quenching technique of spark-erosion. The as-prepared powder consists of amorphous, crystalline, and superparamagnetic particles, mostly as porous aggregates. The major fraction of the powder consists of 20–30 nm particles. A short anneal crystallizes the amorphous particles producing a high moment, >90% of theoretical MS, albeit with HC of a few kOe. If lightly milled, the agglomerates are broken up to yield HC of 1 T. These findings are supported by the x-ray diffraction pattern showing broadened peaks of the predominant LTP-MnBi phase. The combination of spark erosion, milling, and annealing has produced randomly oriented particles with (BH)MAX ∼ 3.0 MGOe. The particles are expected to show record energy product when aligned along their crystallographic easy axes.