is explained by a redistribution of magnetic phases along the easiest magnetization axes closest to the tension axis, fragmentation of domains, and increased mechanical stress gradients. The contribution of changes in the energy of interdomain boundaries of the deformable material to the coercive force Hc is taken into account [1, 2]. It would seem justified for materials such as iron and cobalt with the anisotropy energy K1 by an order of magnitude higher than the magnetoelastic energy λ100⋅σ, that is, for K1 > λ100⋅σ. However, in [3, 4] it was demonstrated that under tension of a cobalt uniaxial single crystal along the easy magnetization axis, the width of its domains was changed. The authors believed that this was due to changes in the energy of the interdomain boundaries. It is natural to consider that this factor can noticeably contribute to the Hc magnitude of loaded materials. It seems likely that the contribution of this mechanism to the coercive force Hc can be estimated fairly correctly for materials whose anisotropy energy is comparable with the magnetoelastic energy, that is, for λ100⋅σ ~ K1. For high-striction materials, the contribution of the magnetoelastic energy to the energy of the interdomain boundary can be quite noticeable. To check this assumption, we investigated the dependence of the coercive force of TbFe2 samples on the elastic compressing stress. The alloys were melted in an electroarc furnace with a nonexpendable tungsten electrode. The melted metal was poured into a cylindrical mold 6 mm in diameter. Samples with length L = 5.6–13.4 mm were cut from ingots so produced. The coercive force was measured with a ferroprobe (an indicator of sample demagnetization) having dimensions of 2.5 × 0.7 mm and with a magnetometer along and transverse the sample. Figure 1 shows the block diagram of the experimental setup. The compressing force F was applied to examined sample 3 using bronze guide bars 4. The sample was put into the channel of solenoid 1 with magnetizing windings 2. Magnetic field pickup (ferroprobe) 5 of magnetometer M was placed in the solenoid center perpendicular to the sample axis. The solenoid winding contained 690 turns of PEV-0.6 wire. The coercive force Hс of the sample was calculated from the demagnetization current Id and the solenoid constant. The standard procedure of measuring Id was used. It involved preliminary three-pulse magnetization (at magnetization current Im = 2 A), registration of the field Hr of the residually magnetized sample, and sample demagnetization down to zero value of Hr. The ferroprobe was placed in the solenoid in the region having a minimum sensitivity to its field (less than 2% of the maximum value of Hr by the magnetometer scale). The compressing force was produced by a rupture-testing machine with a limiting load of 10 kN. The coercive forces Hс were measured successively in two directions: parallel (Hc || ) and perpendicular (Hc ⊥ ) to the direction of force application to the sample. To measure Hc ⊥ , the sample was placed in the central channel perpendicular to the magnetization field. Before each loading series, the sample was demagnetized from a field of 100 kA/m to destruct the magnetic structure formed under the preceding load. Results of investigations of the dependence Hc(σ) shown in Fig. 2 demonstrate that Hc || , measured along the compression direction, first increases, reaches its maximum, and then decreases almost linearly. Hc ⊥ , measured in the
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Dec 12, 2016
Li Peng + 2
Open Access
