Tuning Easy Magnetization Direction and Magnetostatic Interactions in High Aspect Ratio Nanowires

Cobalt nanowires have been synthesized by electrochemical deposition using track-etched anodized aluminum oxide (AAO) templates. Nanowires with varying spacing-to-diameter ratios were prepared, and their magnetic properties were investigated. It is found that the nanowires’ easy magnetization direction switches from parallel to perpendicular to the nanowire growth direction when the nanowire’s spacing-to-diameter ratio is reduced below 0.7, or when the nanowires’ packing density is increased above 5%. Upon further reduction in the spacing-to-diameter ratio, nanowires’ magnetic properties exhibit an isotropic behavior. Apart from shape anisotropy, strong dipolar interactions among nanowires facilitate additional uniaxial anisotropy, favoring an easy magnetization direction perpendicular to their growth direction. The magnetic interactions among the nanowires were studied using the standard method of remanence curves. The demagnetization curves and Delta m (Δm) plots showed that the nanowires interact via dipolar interactions that act as an additional uniaxial anisotropy favoring an easy magnetization direction perpendicular to the nanowire growth direction. The broadening of the dipolar component of Δm plots indicate an increase in the switching field distribution with the increase in the nanowires’ diameter. Our findings provide an important insight into the magnetic behavior of cobalt nanowires, meaning that it is crucial to design them according to the specific requirements for the application purposes.

Highly spin-polarized electronic structure and magnetic properties of Mn2.25Co0.75Al1−xGex Heusler alloys: first-principles calculations

The complete spin polarizations of Mn2.25Co0.75Al1−xGex are proved to be robust against stoichiometric defect and lattice deformation, whose easy magnetization direction can be manipulated from in-plane direction to out-of-plane one under uniaxial strain.

Dynamic magnetoelastic properties of TbxHo0.9−xNd0.1(Fe0.8Co0.2)1.93/epoxy composites

TbxHo0.9−xNd0.1(Fe0.8Co0.2)1.93/epoxy (0 ⩽ x ⩽ 0.40) composites are fabricated in the presence of a magnetic field. The structural and dynamic magnetoelastic properties are investigated as a function of both magnetic bias field Hbias and frequency f at room temperature. The composites are formed as textured orientation structure of 1–3 type with 〈1 0 0〉 preferred orientation for x ⩽ 0.10 and 〈1 1 1〉-orientation for x ⩾ 0.25. The composites generally possess insignificant eddy-current losses for frequency up to 50 kHz, and their dynamic magnetoelastic properties depend greatly on Hbias. The elastic modulus (E3H and E3B) shows a maximum negative ΔE effect, along with a maximum d33, at a relatively low Hbias ~ 80 kA/m, contributed by the maximum motion of non-180° domain-wall. The 1–3 type composite for x ⩾ 0.25 shows an enhanced magnetoelastic effect in comparison with 0 to 3 type one, which can be principally ascribed to its easy magnetization direction (EMD) towards 〈1 1 1〉 axis and the formation of 〈1 1 1〉-texture-oriented structure in the composite. These attractive dynamic magnetoelastic properties, e.g., the low magnetic anisotropy and d33,max as high as 2.0 nm/A at a low Hbias ~ 80 kA/m, along with the light rare-earth Nd element existing in insulating polymer matrix, would make it a promising magnetostrictive material system.

Magnetoelastic properties of epoxy resin based TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 particulate composites

TbxHo0.9−xNd0.1 (Fe0.8Co0.2)1.93 (0 ⩽ x ⩽ 0.40) particulate composites were prepared by embedding and aligning alloy particles in an epoxy matrix with and without a magnetic curing field. The magnetoelastic properties were investigated as functions of composition, particle volume fraction and macroscopic structure of the composite. The magnetic anisotropy compensation point was found to be around x = 0.25, where the easy magnetization direction (EMD) at room temperature was detected lying along ⟨ 1 1 1 ⟩ axis. The composite with ⟨ 1 1 1 ⟩ preferred orientation and pseudo-1-3 type structure was prepared under an applied magnetic field of 12 kOe. An enhanced magnetoelastic effect and large low-field magnetostriction λa, as high as 430 ppm at 3 kOe, were obtained for Tb0.25Ho0.65Nd0.1 (Fe0.8Co0.2)1.93 composite rod. The value of λa was of 72 % of its polycrystalline alloy (~595 ppm/3 kOe) although it only contained 30 vol.% of the alloy particles. This enhanced effect can be attributed to the larger λ111 (as compared to λ100), low magnetic anisotropy, easy magnetization direction (EMD) along the ⟨ 1 1 1 ⟩ axis and ⟨ 1 1 1 ⟩-textured orientation of the alloy particles as well as the chain-like structure of the composite. The good magnetoelastic properties of the composite, in spite of the fact that it contained only 30 vol.% of the alloy particles with light rare-earth Nd element in the insulating epoxy, would make it a potential material for magnetostriction application.

Lattice and Magnetic Anisotropies in Uranium Intermetallic Compounds

Examples of UNiAlD2.1 and UCoGe illustrate that the soft crystallographic direction coincides quite generally with the shortest U-U links in U intermetallics. It leads to a simple rule, that the easy magnetization direction and the soft crystallographic direction (in the sense of highest compressibility under hydrostatic pressure) must be mutually orthogonal.

Magnetic Properties of a HoFe5Al7 Single Crystal

A single crystal of HoFe5Al7 (tetragonal ThMn12 structure) has been studied. HoFe5Al7 orders ferrimagnetically at TC = 227 K and has a compensation of the Ho and Fe sublattices at Tcomp = 65 K. The compound exhibits high easy-plane anisotropy. Strong anisotropy is also present within the basal plane, with the [110] axis being the easy magnetization direction. A high coercivity with Hc values attaining 1.6 T is found at 2 K. In the temperature range 40-80 K, HoFe5Al7 displays a field-induced magnetic transition along the easy [110] direction. Temperature dependence of the critical field Hcr of the transition is very strong, Hcr exceeds 14 T below 40 K.