Formation Of Non-magnetic Phase Research Articles

Phase transformation and magnetic properties of rapidly solidified Mn-Al-C alloys modified with Zr

Mn54−xAl43C3Zrx (x = 1, 3) alloys were prepared by rapid solidification followed by heat treatment to produce the ferromagnetic τ phase. The substitution of Zr for Mn in the structure resulted in an increase of the saturation magnetization (Ms) compared to that of Mn54Al43C3. While the highest Ms (128 ± 1 emu/g) was obtained in Mn53Al43C3Zr1, the coercivity was also improved to 1.62 kOe, compared to 1.25 kOe for Mn54Al43C3. To further improve the coercivity through grain refinement, additional C (1%, 3%, 5%, and 7%) was added to Mn53Al43C3Zr1. An increase in the coercivity was observed due to a decrease of grain size and the formation of nonmagnetic phases, which reduced the magnetostatic interactions between the τ-phase grains. However, excess C reduced the saturation magnetization due to the formation of the other non-ferromagnetic phases, including ε, γ2, and β phases.

Influence of isochronal annealing on the microstructure and magnetic properties of Cu-free HITPERM Fe40.5Co40.5Nb7B12 alloy

Systematic study of the effect of isochronal annealing on the structure and magnetic properties of Cu-free HITPERM alloy (Fe40.5Co40.5Nb7B12) is described herein. Mössbauer spectroscopy (MS) and anomalous x-ray diffraction (XRD) measurement at Fe K-edge (7.112 keV) jointly provide clear evidence for the presence of atomically ordered α′-FeCo (B2 structure) phase as a nanocrystalline ferromagnetic phase. Being a short range order probe, Mössbauer spectroscopy also confirms the development of an additional non-magnetic Nb-rich phase in the nanocrystalline specimens (annealed above 723 K) with simultaneous lowering of the volume fraction of ferromagnetic phases. The fraction of Fe atoms in the non-magnetic phase is ∼15% upon annealing at 773 K for 1 h, which increases gradually and reaches to as high as ∼19% after annealing at 923 K. This phase was not detected by XRD and transmission electron microscopy (TEM) measurements, which may be attributed to tiny crystallite size and/or high degree of disorder. In the second stage of crystallization, i.e., above 923 K, the alloy becomes fully crystalline and a stable, hard magnetic fcc-(FeCo)23B6 type phase was observed as a main boride phase along with soft magnetic α′-FeCo phase and Nb rich non-magnetic phase. Thermo magnetic measurement evidenced re-crystallization process as a considerable decrease in magnetization at the second transformation stage. Simultaneous lowering of the volume fraction of magnetic phases with the formation of non-magnetic phase provides convincing origin for the decrease in magnetization at the second crystallization stage.

Influence of multilayer modulation on structural and magnetic features in the Pt/Sm–Co system

In this work, we study the influence of Pt underlayer in Pt/Sm–Co/Pt trilayers and in Pt/Sm–Co multilayers. In both cases, Pt underlayer seems to impose better crystallinity to Sm–Co layer and certainly promotes the evolution of the hard-magnetic SmCo 5 phase. Particularly, in the case of multilayer form, where multiple interlayers of Pt each one serving as a dedicated underlayer for the deposition of a specific Sm–Co layer, enhanced crystallinity is observed. Moreover, post-deposition annealing facilitates these features at relatively lower temperatures (∼400 °C) than those met in thin-film cases. This behavior is also followed by enhancement of saturation magnetization, while higher temperature post-deposition thermal treatment seems to deteriorate structural and magnetic features. If annealing temperature gets over 550 °C macroscopic magnetic features depress, probably due to domination of annealing-activated processes such as Sm oxidation and formation of non-magnetic phases since Pt diffuses throughout the whole magnetic layer.

Effect of nanoscale thin films of Dy 2Fe 14B on the magnetic hysteresis characteristics of melt-spun ribbons of Nd 2Fe 14B

The effectiveness of nanoscale Dy 2Fe 14B thin films on coercivity and energy product of melt-spun ribbons of Nd 2Fe 14B at high temperatures was investigated. It is hypothesized that the nanoscale Dy-thin film will act as an obstacle for the nucleation of reverse domains and also maximize the energy of domain walls and thereby improve the magnetic performance at high temperatures. Pulsed laser deposition (PLD) of amorphous Dy 2Fe 14B layers on Nd 2Fe 14B melt-spun ribbons was performed for a nominal thickness of 40 nm. The coated ribbons were then annealed in environmentally controlled quartz furnace at two different cycles (750 °C for 15 min and 900 °C for 2 h) to cause crystallization. Magnetic hysteresis tests conducted at 300 and 400 K revealed that there is small but consistent improvement in the magnetic properties of the coated ribbons annealed at 750 °C for 15 min. However, higher temperature annealing (900 °C for 2 h) drastically reduced the magnetic properties. The incomplete recrystallization of amorphous structure at 750 °C for 15 min and large grain growth and formation of non-magnetic phases at 900 °C for 2 h are believed to be responsible for not meeting the expected magnetic performance.

LaSr-manganate powders and bulk material by crystallization of a glass

Abstract LaSr-manganate (LaSr)MnO 3 with perovskite structure was prepared in the basic system MnO 2 –SrO–La 2 O 3 –B 2 O 3 (–SiO 2 ) by a modified glass crystallization method. X-ray diffraction, magnetic measurements, EDX and particle size investigations (specific surface) were carried out. The influence of the annealing conditions on the phase composition and the magnetic properties of the powders are discussed. In the silicate-free system manganate powder samples show values of specific saturation magnetization up to 53 Am 2 /kg, a Curie temperature between 369 and 389 K and a mean particle size in the order of 100 nm. The powders reveal the magneto-resistive effect. In the silicate system the borate phase was leached out to get a manganate-SiO 2 mixture which could be sintered to bulk samples. The sintering conditions have been varied to avoid a decrease of the magnetization due to the formation of non-magnetic phases. Sintered samples show a superposition of the CMR and the GMR effect due to grain boundaries.