Strain-induced Magnetization Research Articles

Investigation of strain-induced magnetization change in ferromagnetic microparticles

This work is devoted to investigation of magnetoelastic strain effect on the ferromagnetic microparticles of permalloy. An original method of sample fabrication with compressed microparticles is proposed. Magnetic force microscopy and magneto-optical Kerr experiments were carried out with unstrained and compressed microparticles. The domain walls transformation in compressed microparticles is in good agreement with numerical calculations. Hard axis of magnetization was observed on the compressed sample.

Reversible strain-induced magnetization switching in FeGa nanomagnets: Pathway to a rewritable, non-volatile, non-toggle, extremely low energy straintronic memory.

We report reversible strain-induced magnetization switching between two stable/metastable states in ~300 nm sized FeGa nanomagnets delineated on a piezoelectric PMN-PT substrate. Voltage of one polarity applied across the substrate generates compressive strain in a nanomagnet and switches its magnetization to one state, while voltage of the opposite polarity generates tensile strain and switches the magnetization back to the original state. The two states can encode the two binary bits, and, using the right voltage polarity, one can write either bit deterministically. This portends an ultra-energy-efficient non-volatile “non-toggle” memory.

Tensile strain-induced magnetism transition in multilayer graphene with excess electrons: Stability of the edge-quantum well

The stability of edge-quantum well-induced strong magnetism of multilayer armchair graphene nanoribbon (AGNR) with excess electrons was investigated under applied tensile strain by density functional theory (DFT) calculations. The results indicated that: (1) The strain along the armchair edge direction led to a transition of the multilayer AGNRs from ferromagnetic state to nonmagnetic state when the strain increased to a critical value; (2) The strain induced bond length changes reduced the stability of the edge-quantum well in terms of the reduction of the electrons capturing capacity; and (3) The spin splitting of the energy bands near the Fermi level reduced with the increase of the strain, resulting in the decrease of the spin moment. This finding suggests that the magnetic properties of graphene have strong dependence on its strain states, which is crucial to the design of graphene-based magnetic devices.

Fast strain wave induced magnetization changes in long cobalt bars: Domain motion versus coherent rotation

A high frequency (88 MHz) traveling strain wave on a piezoelectric substrate is shown to change the magnetization direction in 40 μm wide Co bars with an aspect ratio of 103. The rapidly alternating strain wave rotates the magnetization away from the long axis into the short axis direction, via magnetoelastic coupling. Strain-induced magnetization changes have previously been demonstrated in ferroelectric/ferromagnetic heterostructures, with excellent fidelity between the ferromagnet and the ferroelectric domains, but these experiments were limited to essentially dc frequencies. Both magneto-optical Kerr effect and polarized neutron reflectivity confirm that the traveling strain wave does rotate the magnetization away from the long axis direction and both yield quantitatively similar values for the rotated magnetization. An investigation of the behavior of short axis magnetization with increasing strain wave amplitude on a series of samples with variable edge roughness suggests that the magnetization reorientation that is seen proceeds solely via coherent rotation. Polarized neutron reflectivity data provide direct experimental evidence for this model. This is consistent with expectations that domain wall motion cannot track the rapidly varying strain.

Strain-induced edge magnetism at the zigzag edge of a graphene quantum dot

We study the temperature dependent magnetic susceptibility of a strained graphene quantum dot using the determinant quantum Monte Carlo method. Within the Hubbard model on a honeycomb lattice, our unbiased numerical results show that a relative small interaction $U$ may lead to an edge ferromagneticlike behavior in the strained graphene quantum dot. Around half-filling, the ferromagnetic fluctuations at the zigzag edge are strengthened both by the on-site Coulomb interaction and the strain, especially in the low temperature region.

Strain-Induced Magnetism in Single-Layer MoS2: Origin and Manipulation

We investigate the strain-induced electronic and magnetic properties of single-layer (1L) MoS2 with vacancy defects using the density functional theory calculation. When the tensile strain is applied, 1L-MoS2 with vacancy becomes ferromagnetic and metallic. We elucidate that, from the electronic band structure of vacancy-defect-doped 1L-MoS2, the impurity bands inside the gap play a role of seed to drive novel magnetic and electronic properties as the strain increases. In particular, we also find that 1L-MoS2 with two-sulfur vacancy (V2S) shows the largest magnetic moment at ∼14% strain among various vacancy types and undergoes a spin reorientation transition from out-of-plane to in-plane magnetization at ∼13% strain. This implies that the strain-manipulated 1L-MoS2 with V2S can be a promising candidate for new spintronic applications.

Magnetoelastic effect during the low-temperature deformation of 316LN-IG stainless steel

The segments of tubes made of austenitic 316LN-IG stainless steel that are cut along the tube axis are subjected to tensile tests in liquid and gaseous helium at temperatures below 7 K. The tubes are intended for the conductor conduits of the toroidal magnetic system of ITER. The time evolution of the strain, the temperature, and the strain-induced magnetization of specimens in the form of the normal component of the magnetic field on their surfaces is studied as a function of the applied load. The behavior of local deformation near slip bands is complicated: the areas near slip planes undergo unloading and shrinking. A magnetoelastic effect is detected; it indicates a negative longitudinal magnetostriction for the initial γ phase and the strain-induced α phase. The cases of absent local heating during strain jumps are explained by the magnetocaloric effect in the areas unloaded during slip.

Strain-induced magnetism in MoS2 monolayer with defects

The strain-induced magnetism is observed in single-layer MoS2 with atomic single vacancies from density functional calculations. Calculated magnetic moment is no less than 2 μB per vacancy defect. The strain-induced band gap closure is concurrent with the occurrence of the magnetism. Possible physical mechanism of the emergence of strain-induced magnetism is illustrated. We also demonstrate the possibility to test the predicted magnetism in experiment. Our study may provide an opportunity for the design of new type of memory-switching or logic devices by using earth-rich nonmagnetic materials MoS2.

Strain-induced magnetization reorientation in epitaxial Cu/Ni/Cu rings

The role of the strain state in epitaxial (001)-oriented Cu/Ni(14 nm)/Cu rings is investigated using a combination of magnetic force microscopy and finite-element calculations. Rings with an external diameter of 3 and 2 $\ensuremath{\mu}$m and linewidth $W$ larger than 400 nm show two different structures: domains with magnetization oriented in the radial direction exist at the inner and outer radius, separated by an area in the interior of the ring consisting of stripe domains with perpendicular magnetization. The former is the sole magnetic structure observed for $W<400$ nm. Micromagnetic calculations on narrow-linewidth structures indicate that the radial domain-wall structure consists of elliptical Bloch lines with a shorter and longer length along the tangential and radial directions, respectively. Finite-element calculations show that the anisotropic relaxation of the in-plane strain is larger at the ring inner and outer edges than in the interior part of the ring and accounts for the reorientation of the magnetization direction.

Voltage-Controlled Uniaxial Magnetic Anisotropy in Soft Magnetostrictive Ferromagnetic Thin Films

A push-pull type ferromagnetic (FM)/ferroelectric (FE) composite was realized with depositing soft magnetostrictive amorphous (Fe65Co35)80B20 alloy on top of the microfiber lead zirconate titanate commercial composite. The piezoelectric and magnetic hysteresis loops of the FM/FE composite were measured with different electric field polarization. We report a remarkable large converse magnetoelectric effect at room temperature including reversible tuning of the in-plane uniaxial anisotropy. The experimental results were analyzed based on strain-induced magnetization change theory. For this purpose, the applied stress to FM resulting from the piezoelectric strain of FE and the saturation magnetostriction of FM were evaluated. The results indicate a high magnetostriction constant value of 110 ppm and moderate useful applied stress of ± 50 MPa. We conclude that the combination of soft magnetostrictive FM with push-pull type piezoelectric FE is suitable for ultralow power electric field writable or tunable electronic devices.

Strain-induced magnetization change in patterned ferromagnetic nickel nanostructures

We report strain-induced coercive field changes in patterned 300 × 100 × 35 nm3 Ni nanostructures deposited on Si/SiO2 substrate using the magnetoelastic effect. The coercive field values change as a function of the applied anisotropy strain (∼1000 ppm) between 390 and 500 Oe, demonstrating that it is possible to gradually change the coercive field elastically. While the measured changes in coercive field cannot be accurately predicted with simple analytical predictions, fairly good agreement is obtained by using a micromagnetic simulation taking into account the influence of nonuniform strain distribution in the Ni nanostructures. The micromagnetic simulation includes a position dependant strain-induced magnetic anisotropy term that is computed from a finite element mechanical analysis. Therefore, this study experimentally corroborates the requirement to incorporate mechanical analysis into micromagnetic simulation for accurately predicting magnetoelastic effects in patterned ferromagnetic nanostructures.

직교자계가 디펌성능에 미치는 영향

An orthogonal magnetic field is often used for a military vessel in the deperm process such as Flash D deperm protocol and Anhysteretic deperm protocol. The effect of the orthogonal magnetic field on a deperm performance was investigated for a sample with strain-induced magnetization and field-induced magnetization given to different direction. A 70mm wide, 110mm long and 0.25mm thick rectangular steel plate was bent to have U-shape and to generate a strong strain on the bottom region of U-shaped steel plate. Field-induced magnetization was attached by NdFeB permanent magnet. Demagnetization was performed by applying magnetic field with a step decrement from the first field(the first shot) under the action of DC bias field.

Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

The contributions to the magnetic anisotropy of thin-film rings and lines of width 50 nm and above made from $\text{Ti}(5\text{ }\text{nm})/{\text{Co}}_{0.66}{\text{Cr}}_{0.22}{\text{Pt}}_{0.12}$ (10 and 20 nm)/Ti (3 nm) with a perpendicular magnetocrystalline anisotropy are investigated, using magnetic force microscopy to image the ac-demagnetized state. Four regimes of behavior were observed in both lines and rings. Samples with the largest widths $(>500\text{ }\text{nm})$ showed an out-of-plane maze domain structure typical of unpatterned films with domain widths of $\ensuremath{\sim}200\text{ }\text{nm}$. As the linewidth decreased, a ''bamboo'' domain structure forms in which the domain walls lie approximately perpendicular to the linewidth. Further linewidth decreases result in a reorientation to a net in-plane anisotropy perpendicular to the linewidth, and for the narrowest lines, $<200\text{-nm}$ wide, the anisotropy reorients in plane parallel to the line. The evolution of anisotropy is modeled in terms of contributions from magnetocrystalline, shape, and first- and second-order magnetoelastic terms, and good agreement with experiment is obtained, considering both bulk and surface anisotropy contributions.

Reversible strain effect on the magnetization ofLaCoO3films

The magnetization $(M)$ of a ${\text{LaCoO}}_{3}$ film grown epitaxially on a piezoelectric substrate has been investigated in dependence on the biaxial in-plane strain. $M$ decreases with the reversible release of tensile strain, with a maximum change of at least 6% per 0.1% of biaxial strain near the Curie temperature $({T}_{C})$. The biaxial strain response of ${T}_{C}$ is estimated to be below 5 K/% in the tensile strain state. This is in agreement with results from statically strained films on various substrates. As possible origins of the strain-induced magnetization are considered (i) the strain-dependent Curie temperature, (ii) a strain-dependent magnetically inhomogeneous (phase-separated) state, and (iii) a strain-dependent magnetic moment (spin state) of Co ions. The ${T}_{C}$ shift is found insufficient to explain the measured strain-induced magnetization change but contributions from mechanism (ii) or (iii) must be involved.

Strain-induced magnetization of amorphous ferromagnets

The magnitude of the strain-induced magnetization (ΔBσ effect) of a Fe81.5B13.5Si3C2 amorphous ferromagnetic alloy was studied as a function of the applied magnetic field, the frequency of alternating elastic stress, and the thermomagnetic treatment temperature. It is shown that processes involved in the strain-induced magnetization of the alloy studied are determined by the frequency of alternating elastic stress and the thermomagnetic treatment temperature.

Strain-induced perpendicular magnetization in TbFe 2(1 1 1) thin films on LiNbO 3

By creating the necessary state of epitaxial strain the Laves phase compound TbFe 2 was grown as a thin film with the magnetization perpendicular to the (1 1 1) growth plane onto a piezoelectric substrate. The material was deposited by molecular beam epitaxy on LiNbO 3(1 1 1) buffered successively by Ti(0 0 0 1) and then Mo(1 1 0). Differential contraction after growth during cooling to room temperature places the magnetic film under a 0.4% compressive strain, whence magnetoelastic coupling creates the desired magnetic polarization.

Stress/strain distribution around implantation boundaries III. Magnetization distribution around non-implanted discs in ferrimagnetic garnet epilayers supporting bubbles

Abstract The distribution of strain-induced magnetization directions around a nonimplanted disc in an ion-implanted ferrimagnetic garnet epilayer supporting bubbles is derived from the elastic model developed by the author. It is shown that when an in-plane field is applied along a direction close to an in-plane easy-axis, the depth-dependent morphology of charged walls varies strongly with the relative magnitudes of the magnetostriction constants. For λ100 = λ111(λ111<0), the largest charged-wall jump (flip) is expected to occur at the interface between implanted and non-implanted thicknesses. For λ100 = −½λ111, the negative shear strain is demonstrated to favour charged walls pivoting around the in-plane easy-axis in the interface region. A switching mechanism is proposed which explains charged-wall rearrangement at the surface during flip when λ100 is positive.