ISSN 0031918X, The Physics of Metals and Metallography, 2011, Vol. 112, No. 1, pp. 13–24. © Pleiades Publishing, Ltd., 2011. Original Russian Text © L.L. Afremov, Yu.V. Kirienko, 2011, published in Fizika Metallov i Metallovedenie, 2011, Vol. 112, No. 1, pp. 15–27. 13 1. INTRODUCTION The concept of remanence as a metastable state of a magnet has been formulated sufficiently long ago (see, e.g., [1, p. 852]). The relationships between the reversible and irreversible initial susceptibilities, as well as the dependence of the remanence on the sequence in which the magnetic field and mechanical stresses were applied, have been studied still as long ago as in the experimental works of Kondorskii [2, 3]. At the same time, it has been shown in [4, 5] that the initial susceptibility of single crys tals of meteoritic iron depends of the sequence of the application and removal of the elastic load and of the switching on and switching off of the magnetic field. The results of the investigation of the effect of the sequence of the application and removal of the elastic load and magnetic field on the process of magnetization of polycrystalline samples of iron, nickel, and silicon iron alloys have been described in detail in [6]. Similar studies were also performed using natural fer romagnets (see, e.g., [7–11]). If the uniaxial mechanical stresses are applied (σ + ) or removed (σ 0 ) in the presence of a magnetic field (H + ) or without a magnetic field (H 0 ), then there arises a socalled piezoremanent magnetiza tion I r (H + σ + σ 0 H 0 ) [11]. This magnetization can exceed both the normal remanence I r (H) = I r (H + H 0 ) and the piezoremanence I r (σ + H + H 0 σ 0 ) obtained in the field of mechanical stresses. It was experimentally shown in [8–10] that in the range of low fields and mechanical stresses (H ≤ 20 Oe, σ ≤ 120 kgf/cm 2 ) the magnetization I r (H + σ + σ 0 H 0 ) is proportional to the field H and stresses σ, whereas I r (σ + H + H 0 σ 0 ), just as the normal remanence, is proportional to H 2 . It was also noted in [8–10] that the piezoremanence depends on the mutual orientation of the magnetic field and mechanical stresses. The trans verse piezoremanence (arising in a field H ⊥ σ) in the case of small stresses is always less (by 10–25%) than the longitudinal magnetization formed in a field parallel to stresses: I r (H + σ + σ 0 H 0 ) < I r (σ + H + H 0 σ 0 ). The effects of plastic deformations on the magnetiza tion processes were studied in much detail in a series of works [12–15] that represent the dependence of the ini tial susceptibility χ, remanence I r , and coercive force H c of various steels on the elastic and plastic deformations. The measurements of I r and H c showed that the behavior of these characteristics in a field of elastic stresses depends substantially on into what “zero” state the sam ples were led, i.e., whether the curves are taken in the presence of mechanical stresses (in a loaded state) or after the stress is removed (in the unloaded state). Note that in the range of stresses exceeding the elastic limit the rema Effect of Elastic and Plastic Deformations on the Remanent Magnetization of an Ensemble of Nanoparticles L. L. Afremov and Yu. V. Kirienko FarEast Federal University, ul. Sukhanova 8, Vladivostok, 690950 Russia Received July 2, 2010 Abstract—A theoretical investigation of the effect of mechanical stresses on the remanent magnetization has been performed in terms of the model of singledomain noninteracting nanoparticles. Relationships have been obtained which define two main types of remanence in the entire range of stresses. In the lowfield approximation, the magnetization of the first type, whose mechanism of formation is similar to that of the normal remanence, is quadratic in both the magnetic field and stresses and only slightly changes with increas ing stresses. Depending on the relationship between the magnetostriction constants, this magnetization can both increase and decrease with increasing stresses. The magnetization of the second type, which arises as a result of a nonmonotonic behavior of the critical fields of nanoparticles depending on mechanical stresses, is proportional to the magnetic field and mechanical stresses. It has been shown that the longitudinal rema nence arising in the field of stresses parallel to the magnetic field is always greater than the transverse rema nence. The behavior of the remanence with increasing mechanical stresses depends substantially on whether this magnetization is formed in a loaded state or in a state unloaded after plastic deformation. In the range of deformations where the anisotropy of the applied stresses is less than the magnetocrystalline anisotropy, the plastic tension should lead to a decrease in the magnetization as compared to that arising in the plastically undeformed state. Plastic compression can lead to both an increase and a decrease in the remanence. Keywords: remanence, piezoremanence, ensemble of nanoparticles, mechanical stresses, residual stresses, elastic deformation, plastic deformation, critical field DOI: 10.1134/S0031918X11040028 THEORY OF METALS