We review different electron transport methods to probe the magnetic properties, such as the magnetic anisotropy, of an individual Fe4 SMM. The different approaches comprise first and higher order transport through the molecule. Gate spectroscopy, focusing on the charge degeneracy-point, is presented as a robust technique to quantify the longitudinal magnetic anisotropy of the SMM in different redox states. We provide statistics showing the robustness and reproducibility of the different methods. In addition, conductance measurements typically show high-energy excited states well beyond the ground spin multiplet of SMM. Some of these excitations have their origin in excited spin multiplets, others in vibrational modes of the molecule. The interplay between vibrations, charge and spin may yield a new approach for spin control.
Hybrid straintronics and voltage-controlled-magnetic-anisotropy: Precessional switching of a perpendicular anisotropy magneto-tunneling junction without a magnetic field
Fe3O4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple ana…
The orientation of the tilted magnetic anisotropy has crucial importance in many spintronic devices. However, it is very challenging to determine it especially in very small structures produced by lithography. Here, we propose a new experimental method to directly and accurately measure both the polar and azimuthal angles of a tilted magnetic anisotropy. By using the proposed experimental method, we have successfully determined the out-of-plane and in-plane angles of the tilted magnetic anisotropy in a micro-structured multilayer thin film. The orientation of the tilted magnetic anisotropy in …
Magnetic nanorings have been widely studied due to their potential applications in spintronic and magnonic devices. In this work, by means of analytical calculations and micromagnetic simulations we have analyzed the magnetic energy of nanorings with variable anisotropy along their radius. Four magnetic states, including two new magnetic configurations, here called meron and knot-like states, are considered, looking to the relative lower energy states as a function of anisotropy. Phase diagrams with this states are presented.
Based on the micromagnetic simulations the magnetization switching in a triangle magnetic element by voltage-control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction under in-plane magnetic field is proposed. The proposed switching scheme is not the toggle switching but the deterministic switching where the magnetic state is determined by the polarity of the applied voltage pulse. The mechanism and conditions for the switching are clarified. The results provide a fast and low-power writing method for magnetoresistive random access memories.
We study the tunneling magnetoresistance in the ensembles of ferromagnetic granules with random easy axes of magnetic anisotropy taking into account the exchange interaction between granules. It is shown that due to the exchange interaction magnetoresistance is effectively decoupled from magnetization, i.e. the strongest negative magnetoresistance can be observed at the field where magnetization is almost saturated. Under some conditions, the sign of magnetoresistance can be reversed and tunneling magnetoresistance can become positive at certain magnetic fields. Our theory agrees with measurem…
We demonstrate directional dependence of the self-modification of internal mesospin textures in magnetic metamaterials, arising from the coupling of the atomic- and mesoscopic length-scales. Dressing the mesospins in different directions enables the quantification of the degree of texture in the internal magnetization and its impact on the interaction energy of the mesospins. The emerging anisotropy is manifested in a directional dependence of the remanent magnetization with temperature.
Controlling magnetic anisotropy is a key requirement for the fundamental understanding of molecular magnetism and is a prerequisite for numerous applications in magnetic storage, spintronics, and all-spin logic devices. In order to address the question of molecular magnetic anisotropy experimentally, we have synthesized single-crystals of a molecular spin system containing four antiferromagnetically coupled s = 5/2 manganese(II) ions. Using low-temperature cantilever magnetometry, we demonstrate the selective population of the S = 0, 1, . . . , 10 spin states upon application of magnetic field…
A low power magnetization switching scheme based on the voltage control of magnetic anisotropy (VCMA) is proposed. In contrast to the conventional switching scheme using VCMA, where the magnetic anisotropy is eliminated during the voltage pulse, the magnetic anisotropy is enhanced to induce precession around the axis close to the easy axis. After turning off the voltage proximately at a half of precession period, the magnetization relaxes to the opposite equilibrium direction. We perform numerical simulations and show that the pulse duration of the proposed switching scheme is as short as a fe…
The magnetic response of nanostructures plays an important role on biomedical applications being strongly influenced by the magnetic anisotropy. In this work we investigate the role of temperature, particle concentration and nanoparticle arrangement forming aggregates in the effective magnetic anisotropy of Mn-Zn ferrite-based nanoparticles. Electron magnetic resonance and coercivity temperature dependence analyses, were critically compared for the estimation of the anisotropy. We found that the temperature dependence of the anisotropy follows the Callen-Callen model, while the symmetry depend…
Enhancement of magnetic anisotropy barrier in long range interacting spin systems
磁性材料通常以各向异性能垒为特征，各向异性能垒决定了磁化衰减的时间尺度，从而决定了样品的磁稳定性。在这里，我们提出了一个统一的描述，其中包括相干旋转和成核，在一般的各向异性自旋系统的磁化衰减。特别是，我们表明，在存在的长程交换相互作用，各向异性能垒增长的体积的粒子上的各向异性，而它的增长速度甚至比体积交换各向异性，与各向异性能垒成正比的$V^{2-α/d}$，其中$V$是粒子体积，$α\leq d $是相互作用的范围和$d$是嵌入维数。这些结果表明，各向异性能垒w.r.t.短程情况，其中对于大颗粒尺寸或大颗粒纵横比，各向异性能垒随着颗粒横截面积而增长。
Magnetic anisotropy plays an essential role in information technology applications of magnetic materials, providing a means to retain the long-term stability of a magnetic state in the presence of thermal fluctuations. Anisotropy consists of a single-ion contribution stemming from the crystal structure and two-ion terms attributed to the exchange interactions between magnetic atoms. A lack of robust theory crucially limits the understanding of the temperature dependence of the anisotropy in pure two-ion and mixed single-ion and two-ion systems. Here, we use Green's function theory and atomisti…
Planar array of self-assembled Ga$_{x}$Fe$_{4-x}$N nanocrystals in GaN: Magnetic anisotropy determined via ferromagnetic resonance
用铁磁共振方法研究了镶嵌在GAN基质中的$_{x}$ Fe $_{4-x}$ N纳米晶平面阵列的磁各向异性。采用X射线衍射和透射电子显微镜来确定纳米晶体的相和分布。的磁各向异性被发现主要是单轴的难磁化轴垂直于NC平面，并有一个很弱的面内六角对称。考虑到纳米晶体的形态，外延关系，应变效应和纳米之间的磁耦合的起源的磁各向异性进行了讨论。
