The objective of this project is to develop physical understanding of and modeling for the effect of plastic deformation and texture anisotropy on magnetic properties of ferromagnetic polycrystalline materials, both in bulk and film form. In 2008 we experimentally focused on the plastic properties of ion beam sputtered thin films on superelastic nitinol sheet metal templates. Stress was applied to the samples in two different ways: (1) Axial stretching in an Instron materials tester; (2) Stretching of the material by bending the sample over a rod with a well-defined diameter. The first method led to an inhomogeneous strain distribution in the sample with areas of large (+5.5%) strain and areas of low (<1%) strain. The thin film would come off the substrate in the areas of large strain. The 2 nd method led to a more homogeneous strain distribution in the thin film; the thin film would not come off the substrate up to a strain of 5.5% and no transformation fronts could be observed with a video camera. The figures below shows (1) the two used techniques to apply a stress to the thin films (left); (2) the inhomogeneous strain distribution when stressed in the Instron materials tester (middle); (3) the macroscopic and microscopic strain-stress curve as measured in the Instron Materials tester. Modeling and Testing the Effects of Texture and Plastic Deformation on Magnetic Properties Martin J. Sablik. Southwest Research Institute, DMR

Modeling and Testing the Effects of Texture and Plastic Deformation on Magnetic Properties Martin J. Sablik. Southwest Research Institute, DMR The properties of the samples were measured before and after the strain cycle. The magnetic properties as measured by VSM are shown in the graphs below. The coercivity decreases perpendicular to the stress axis for the iron thin films but increases perpendicular to the stress axis for permalloy thin films. Existing bulk models will be extended in order to describe these results for magnetic behavior after plastic deformation in thin films, taking into account texture anisotropy. Impact, training and Outreach: A high school student, Daniel Palmer, and three undergraduate students, Clayton Moore, Amanda Gregory, and Kyle Smith worked on this project this year. They received the appropriate safety training to work on the equipment including a general lab safety training, a laser safety training, and radiation safety training. The students presented their work at a meeting of the local chapter of the Society of Physics Students and the Honor’s conference of Texas State University (1 st prize poster presentation), and are planning to present more details of their work at the combined 4CS/TS TexasAPS Fall-2008 meeting, and the MMM-2008 conference. The whole research group was involved in outreach activities to high school seniors and hosted a group of middle school students.

The modeling focused on extending the effect of plastic deformation to the modeling of magnetic Barkhausen noise (HBN) and magnetoacoustic emission (MAE). The models from last year were modified to take into account the effect of dislocation tangles after a plastic deformation of 2% in an iron-silicon alloy. It was assumed that after that deformation is reached, the effect on the dislocation density is renormalized to its value at 2% and that the stress increases less sharply as σ r = (σ ro – σ rc ) │e r │ 2 + σ rc, where the subscript c refers to e=0.02, the point where dislocation tangles begin to set in., and where σ ro = -υ σ F, where ν is a constant similar to Poisson’s ratio in the case of elastic deformation. The strain-hardening stress σ F = A L │e r │ Ln, as given by Ludwik’s law, where L n is the Ludwik exponent, as measured from the initial behavior of the deformation after the yield point, where e r is the residual deformation and where A L is a constant. The results are given below, where Model 1 refers to the model of last year and Model 2 to the present model. The first figure is for HBN, and the second is for MAE. Note that now we are able to fit the HBN more closely, and the new model produces a peak in MAE. A paper on this subject will be published with the Intermag Conf. proceedings in IEEE Transactions on Magnetics. Modeling and Testing the Effects of Texture and Plastic Deformation on Magnetic Properties Martin J. Sablik. Southwest Research Institute, DMR