A P Ring

Publications (7)10.59 Total impact

• Article: Variation of magnetostriction with temperature in Tb5Si2.2Ge1.8 single crystal

  A. P. Ring, H. L. Ziegler, T. Lograsso, D. Schlagel, J. E. Snyder, D. C. Jiles
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  ABSTRACT: The Tb ₅( Si _x Ge _4-x) alloy system is similar to the better known Gd ₅( Si _x Ge _4-x) , except it has a more complex magnetic and structural phase diagram. Gd ₅( Si _x Ge _1-x)₄ has received much attention recently due to its giant magnetocaloric effect, colossal magnetostriction and giant magnetoresistance in the vicinity of a first order combined magnetic-structural phase transition. The magnetostriction changes that accompany the phase transitions of single crystal Tb ₅( Si _2.2 Ge _1.8) have been investigated at temperatures between 20 and 150 K by measurements of magnetostriction along the a axis. Over this temperature range the shape and slope of the magnetostriction curves change, indicative of changes in the magnetic state, crystal structure, and magnetic anisotropy. The results appear to indicate a phase transition that occurs near 106 K (onset-completion range of 116–100 K ). The steepness of the strain transition, its unusual hysteresis, and its temperature dependence appear to indicate a first order phase transition which is activated by applied magnetic field in addition to temperature (see Fig. 1). Magnetostriction measurements at temperature below the transition region appear to indicate a magnetostriction of small overall magnitude (about 30×10^-6 ) but high anisotropy, with anistropy showing considerable temperature dependence.
  Journal of Applied Physics 05/2006; · 2.17 Impact Factor
• Article: Improvement of magnetomechanical properties of cobalt ferrite by magnetic annealing

  C.C.H. Lo, A.P. Ring, J.E. Snyder, D.C. Jiles
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  ABSTRACT: We report dramatic improvements in both magnetostriction level and strain derivative of polycrystalline cobalt ferrite as a result of magnetic annealing. Magnetostrictive cobalt ferrite composites have potential for use in advanced magnetomechanical stress and torque sensors due to their high sensitivity of magnetization to applied stresses and high levels of magnetostriction. Results show that annealing cobalt ferrite at 300°C in air for 36 h under a dc field of 318 kA/m (4 kOe) induced a uniaxial anisotropy with the easy axis being along the annealing field direction. Under hard axis applied fields, the maximum magnetostriction measured along the hard axis at room temperature increased in magnitude from -200×10^-6to -252×10^-6 after annealing. The maximum strain derivative (dλ/dH)_max, which is related to stress sensitivity, increased from 1.5×10^-9 A^-1m to 3.9×10^-9 A^-1m. The results can be interpreted in terms of the effects of induced uniaxial anisotropy on the domain structure and magnetization processes.
  IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
• Source

  Available from: orca.cf.ac.uk

  Article: Mössbauer spectroscopy investigation of Mn-substituted Co-ferrite (CoMnxFe2−xO4)

  K. Krieble, T. Schaeffer, J. A. Paulsen, A. P. Ring, C. C. H. Lo, J. E. Snyder
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  ABSTRACT: Understanding the effect of Mn substitution for Fe in Co ferrite presents a challenge because there are three different transition-metal ions distributed among two distinct crystallographic and magnetic sublattices with complicated superexchange and anisotropic interactions. In this study, a series of six powder samples with compositions Co1.0MnxFe2−xO4 were investigated using transmission Mössbauer spectroscopy. Mössbauer spectroscopy provides an excellent tool for probing the local environment of the Fe atoms present in such materials. Results show two sets of six-line hyperfine patterns for all samples, indicating the presence of Fe in both A and B sites. Identification of sites is accomplished by evidence from hyperfine distribution width, integrated intensity, and isomer-shift data. Increasing Mn concentration was found to decrease the hyperfine field strength at both sites, but at unequal rates, and to increase the distribution width. This effect is due to the relative strengths of Fe–O–X superexchange (X = Fe, Co, or Mn) and the different numbers of the next-nearest neighbors of A and B sites. Results are consistent with a model of Mn substituting into B sites and displacing Co ions onto A sites.
  Journal of Applied Physics 05/2005; 97(10):10F101-10F101-3. · 2.17 Impact Factor
• Article: Manganese-substituted cobalt ferrite magnetostrictive materials for magnetic stress sensor applications

  J. A. Paulsen, A. P. Ring, C. C. H. Lo, J. E. Snyder, D. C. Jiles
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  ABSTRACT: Metal bonded cobalt ferrite composites have been shown to be promising candidate materials for use in magnetoelastic stress sensors, due to their large magnetostriction and high sensitivity of magnetization to stress. However previous results have shown that below 60 °C the cobalt ferrite material exhibits substantial magnetomechanical hysteresis. In the current study, measurements indicate that substituting Mn for some of the Fe in the cobalt ferrite can lower the Curie temperature of the material while maintaining a suitable magnetostriction for stress sensing applications. These results demonstrate the possibility of optimizing the magnetomechanical hysteresis of cobalt ferrite-based composites for stress sensor applications, through control of the Curie temperature.
  Journal of Applied Physics 01/2005; 97(4):044502-044502-3. · 2.17 Impact Factor
• Article: Experimental and modeling studies of the effects of shear stress on magnetization in nickel

  J.A. Paulsen, C.C.H. Lo, J.E. Snyder, A.P. Ring, Y.P. Shen, D.C. Jiles
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  ABSTRACT: The effects of pure shear stress on magnetization in nickel have been studied with a view to developing a theoretical understanding of the Matteucci effect, which is of great technological interest in the search for viable magnetic torque sensors. The effects of pure shear stress on a planar magnetic material and those due to torque applied to a rod are analogous in the sense that they can be described in terms of a pair of tensile and compressive stresses acting at 45° to the neutral axis of the plate or the rod axis. In this work the responses of nickel to shear stresses were studied under various dc applied fields. A model description was developed as a generalization of the theory of magnetomechanical effect to include shear stresses. This theory can be used as an aid to interpretation of the experimental results.
  IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
• Article: Study of the Curie temperature of cobalt ferrite based composites for stress sensor applications

  J.A. Paulsen, C.C.H. Lo, J.E. Snyder, A.P. Ring, L.L. Jones, D.C. Jiles
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  ABSTRACT: Cobalt ferrite has been shown to be an excellent candidate material for high sensitivity magnetic stress sensors due to its large magnetomechanical effect and high sensitivity to strain. However, near room temperature, the material exhibits some magnetomechanical hysteresis, which becomes negligible for temperatures of 60°C and above. Measurements indicate that doping the cobalt ferrite with silicon lowers the Curie temperature of the material. It was also found that the Curie temperature of the material depends on the fabrication and processing procedure. These results offer the possibility of decreasing the room temperature magnetomechanical hysteresis through control of the Curie temperature, thereby altering the temperature dependence of magnetic and magnetomechanical properties.
  IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
• Source

  Available from: cf.ac.uk

  Article: Temperature dependence of magnetic anisotropy in Mn-substituted cobalt ferrite

  Yevgen Melikhov, D.C. Jiles, A P Ring, J.E. Snyder