Mossbauer Spectroscopic Study of High Magnetostrictive Cobalt Chromium Ferrites for Automobile Torque Sensors

Abstract

Co-Cr ferrites with the chemical formulae, CoFe 2-x Cr x O 4 (x = 0 to 0.5 in steps of 0.1) were prepared by sol gel autocombustion method. Lattice constants were determined from X-ray diffraction patterns. Magnetic properties were studied by VSM and Mössbauer spectroscopy. Magnetostrictive coefficients were measured using strain gauge technique. The magnetostriction coefficient has been observed to increase sharply at higher chromium concentrations (x = 0.3 -0.5). The hyperfine field H hf values at B-and A-sites showed an initial increase at both the sites followed by a gradual monotonic decrease with increasing chromium ion concentration (x). The Fe 3+ (B)/Fe 3+ (A) ratio obtained from the Mössbauer spectra decreases with increasing chromium concentration. The results have been explained on the basis of super transferred hyperfine fields.

Crystal strain, chemical bonding, magnetic and magnetostrictive properties of erbium (Er3+) ion substituted cobalt-rich ferrite (Co1.1Fe1.9−xErxO4)

“…The magnetostrictive properties depends upon the processing parameters such as synthesis method, pressure applied while making pellets, sintering atmosphere, temperature and sintering time. 4,[52][53][54][55][56][57][58][59] It is reported that the higher magnetostriction and strain derivatives can be obtained when compacted under high pressure ($150 MPa). [52][53][54][55][56][57][58][59] From Fig.…”

“…4,[52][53][54][55][56][57][58][59] It is reported that the higher magnetostriction and strain derivatives can be obtained when compacted under high pressure ($150 MPa). [52][53][54][55][56][57][58][59] From Fig. 6, it is seen that the magnetostriction coefficient increases with increasing applied magnetic eld and remains almost constant at higher eld, i.e.…”

“…55,56 Although the maximum magnetostriction coefficients for x $ 0.10 in Co 1.1 Fe 1.9Àx Er x O 4 presented a slight decrease, their values are still higher than the other ferrites. 52,[55][56][57][58][59] Recently, Bulai et al have obtained the maximum magnetostrictive coefficient l max ¼ 160 ppm at an applied eld of 7 kOe for Er ¼ 0.03 in bulk CFO. 57 Moreover, the l max obtained at lower eld is 25 ppm and 130 ppm for the applied elds of 2.2 kOe and 4 kOe, respectively.…”

“…58 From the comparative data shown in Table 3, it has been seen that even at lower led (2.2 kOe), the observed values of the magnetostrictive coefficient (l max ) and the strain derivative (dl/dH) max , for x ¼ 0.05 in CFEO, are higher than the any other rare earth substituted in cobalt ferrite. 18,37,[55][56][57][58][59] Furthermore as the strain derivative depends on both the magnetostriction and anisotropy of the material therefore the observed variations in the strain derivative with Er concentration can be understood on the basis of variations of these two parameters. 18,56 The strain derivative can be expressed as:…”

Chromium Substituted Cobalt Ferrites by Glycine-Nitrates Process

“…[33][34][35][36][37] More recent studies consider that the IS values correlated with the structural data can be better used for site assignments in cobalt ferrite. Consequently, the sextet with lower IS (~ 0.19 mm s -1 , relative to -iron) is assigned to iron in tetrahedral sites (from inter-nuclear distance arguments) [35] and the sextet with higher IS (0.32 mm s -1 ) corresponds to octahedral iron sites.…”