Inverse giant magnetoresistance in granular Nd/sub 2/Fe/sub 14/B/α-Fe

Abstract

Partially amorphous Nd-Fe-B ribbons containing 20 or 50 wt% Fe in excess of the nominal composition Nd2Fel,B with 2.9 wt% Cu and 9.7 wt% Zr (referred to Nd,Pe,,B) were prepared by melt-spinning. After a heat treatment the material consists of a mixture of three parts: hard magnetic grains of the Nd,Fel,B phase with a-Fe grains and, in the case of 20 wt% excess Fe, small amounts of a metastable cubic phase, NdzFez3B3. Samples with 20 wt% Fe show a superposition of anisotropic magnetoresistance and giant magnetoresistance (GMR) effects, depending on structural changes caused by heat treatments at various annealing temperatures. For measurements with the applied field both parallel and perpendicular to the sample current an isotropic positive magnetoresistance ratio, MR = [R(H) -R(O)]/R(O), called inverse GMR has been found for samples with 50 wt% excess Fe.

Permanent magnet magnetization state estimation using high frequency signal injection

“…For large electrical resistance variation (>10%) this effect is called giant magnetoresistance (GMR) [25,26]. Magnetoresistance was initially discovered in thin-film structures alternating ferromagnetic and nonmagnetic conductive layers.…”

“…Table I shows typical values of the PM thermal remanent flux coefficient, B  , which is defined as the rate of PM remanent flux variation with temperature [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The coefficient B  is observed to vary significantly for different materials, PM field typically decreasing as the temperature increases [30].…”

“…Citation information: DOI 10.1109/TIA.2016.2541616, IEEE Transactions on Industry Applications from the stator flux linkage; both methods require the machine to be rotating, estimation at standstill being therefore not possible. High frequency signal injection based methods estimate the PM magnetization state from the PM electrical high frequency resistance, which changes with the magnetization state due to the magnetoresistive effect [23][24][25][26][27]. This method can be used over the whole speed range, including standstill.…”

Development of Magnetic Properties during Annealing of Hf_2Co_{11}B Amorphous Alloy

“…NdFe-B alloys are nowadays the most widely used materials in the industry for this purpose [1], moreover addition of iron, dysprosium or terbium is used to improve their properties [2]. The rising prices of rare earth elements facilitates the development of new permanent magnet materials without rare earth elements, for example those with 5d elements, as Mn-Al or Fe-Co [3,4].…”

Crystallization Processes of R_{4.5}Fe_{77}B_{18.5} (R = Pr, Nd) Amorphous Alloys

“…Both later phases appear in the process of recrystallization, immediately after Fe3B formation. Annealing of metallic amorphous precursors, also those containing rare-earth elements, can be a powerful procedure for formation of nanocrystalline magnetic materials [1,2]. Outstanding magnetic properties can be connected with the exchange-coupling between magnetic nanocrystals of two dierent phases: magnetically soft and magnetically hard.…”