Critical properties of mixed spin-1 and spin-5/2 with equal and unequal crystal fields

The effects of assuming equal or unequal crystal fields (CF) on the phase diagrams of a mixed spin-1 and spin-5/2 system are investigated in terms of the recursion relations on the Bethe lattice (BL). The equal CF case was considered for the coordination numbers q=3, 4, and 6, while for q=3 the unequal CF case was also studied. It was found that for the equal CF case, the model exhibits second-order phase transitions and two compensation temperatures for all q, the reentrant behavior for q=4 and first-order phase transitions and tricritical point (TCP) for q=6. In the unequal CF case for q=3, the system yields first- and second-order phase transitions, TCP's, and three compensation temperatures. In addition, the TCP's in a very short range are classified as the stable and unstable ones depending on their free energies.     

Thermal stability of spin valve sensors using artificial Co/Ir based ferrimagnets

Hard-soft spin valve structures have been grown by molecular beam epitaxy on MgO(0 0 1) substrates. The hard magnetic layer consists of an artificial Co/Ir/Co ferrimagnet system (AFi), while a Fe/Co bilayer from the buffer has been used as a soft detection layer. The Fe layer has been grown at 600°C giving rise to a monocrystalline layer with a BCC structure. Consequently, this layer presents a hard and a easy magnetization axis, respectively, along the BCC [1 1 0] and the [1 0 0] directions. The AFi system presents dramatic differences after successive annealing steps up to 350°C. An increase of the GMR from 3% to 3.5% is observed after annealing at 250°C while the coercive field of the AFi and the GMR plateau are strongly reduced. After further annealing at higher temperature the GMR drops down accompanied with a strong decrease in the antiparallel alignment amount in the AFi system. Rutherford back scattering measurements have been performed to investigate the changes in the interface morphology and to correlate it to the magneto-transport properties.     

Switching plasticity in compensated ferrimagnetic multilayers for neuromorphic computing

Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing. In this work, we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin-orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier. Therefore, the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field. Moreover, we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior. This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing.     

Magnetic and mechanical anisotropy in a manganese 2-methylsuccinate framework structure

Hybrid inorganic-organic framework materials exhibit unique properties that can be advantageously tuned through choice of the inorganic and organic components and by control of the crystal structure. We present a new hydrothermally prepared 3D hybrid framework, [Mn(2-methylsuccinate)](n) (1), comprising alternating 2D manganese oxide sheets and isolated MnO(6) octahedra, pillared via syn, anti-syn carboxylates. Powder magnetic characterization shows that the compound is a homospin Mn(II) ferrimagnet below 2.4 K. The easy-axis is revealed by single-crystal magnetic susceptibility studies and a magnetic structure is proposed. Anisotropic elastic moduli and hardness, observed through nanoindentation on differing crystal facets, were correlated with specific structural features. Such measurements of anisotropy are not commonly undertaken, yet allow for a more comprehensive understanding of structure-property relationships.     

Structure and magnetostructural correlation of ferrimagnetic meso-tetraphenylporphinatomanganese(III) dimethyl-N,N′-dicyanoquinone diiminide, [MnTPP]+[Me2DCNQI]·?

The structure [MnⅢ TPP][Me2 DCNQI] (TPP = tetraphenylporphinato; Me 2 DCNQI = 2,5-dimethyl-N,N′-dicyanoquinonediimine) has been determined from X-ray powder diffraction data. The nonsolvated structure is composed of linear (1-D) chains of alternating [MnⅢ TPP] + and μ-[Me 2 DCNQI] with intrachain Mn···Mn separations of 12.83 , and a Mn N DCNQI distance of 2.18. The dihedral angle between the mean Mn(N 4 ) TPP and [Me 2 DCNQI].- planes, and the Mn (N C) DCNQI angle are 84.18° and 143.6°, respectively. [MnⅢ TPP][Me 2 DCNQI] has a T c of 4.3 K from the 10 Hz χ"(T) data, 2-K coercivity of 5,600 Oe, and 6,300 emuOe/mol remnant magnetization that are reduced from that observed for related materials, and their inclusion extends the magnetostructural correlation between the intrachain coupling and both the dihedral angle between the mean Mn(N 4 ) TPP and [TCNE]*- (TCNE = tetracyanoethylene) planes and Mn (N C) TCNE angles. This is in accord with the intrachain coupling arising from the overlap of the MnⅢ d z 2 -like singly occupied molecular orbital (SOMO) and the z component of the [TCNE]*-π* (πz *) SOMO, which increases with decreasing dihedral angle between the mean Mn(N 4 ) TPP and [TCNE]*- planes and Mn (N C) TCNE angle.     

Continuum of compensation points in the mixed spin Ising ferrimagnet with four-spin interaction and next-nearest neighbor coupling

We investigate the magnetic properties of the mixed spin-1/2 and spin-1 Ising ferrimagnetic system with four-spin interaction J₄ and next-nearest neighbor (NNN) coupling J′. We perform exact ground-state calculations and use the finite cluster approximation, based on a single cluster theory, to derive the state equations for the two-dimensional square lattice. The main attention has been paid to the study of the phase diagram for both the transition and compensation temperatures. We find a number of characteristic behaviors. The model with only NNNs induces one compensation point while the four-spin interaction does not. The investigation of the model with both interactions shows a number of characteristic behaviors. In particular, the presence of the four-spin interaction, according to J₄ and J′, may lead to one, two or possibly a continuum of compensation points. This phenomenon may have important applications in technology such as thermomagnetic writing and erasing at the compensation point.     

A Compensation Temperature Induced by Transverse Fields in a Mixed Spin-1 and Spin-3/2 Ising Ferrimagnetic System

A mean-field theory is developed for a mixed Ising ferrimagnetic system consisting of spin 1 and spin 3/2 with different transverse fields. The phase diagram and the thermal behaviour of magnetizations are studied. We find that a compensation point induced by different transverse fields can be observed, although the system never exhibits any compensation point for either zero or uniform transverse fields. The anomalous behaviour of the initial longitudinal magnetic susceptibility in the vicinity of the compensation and critical temperatures is also obtained.     

Optimized growth of compensated ferrimagnetic insulator Gd_3Fe_5O_(12) with a perpendicular magnetic anisotropy

Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic,optical,and microwave devices.Among many different garnets,Gd_3 Fe_5 O_(12)(GdIG) is a representative compensated ferrimagnetic insulator.In this paper,we will study the evolution of the surface morphology,the magnetic properties,and the magnetization compensation through changing the following parameters:the annealing temperature,the growth temperature,the annealing duration,and the choice of different single crystalline garnet substrates.Our objective is to find the optimized growth condition of the GdIG films,for the purpose of achieving a strong perpendicular magnetic anisotropy(PMA) and a flat surface,together with a small effective damping parameter.Through our experiments,we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700℃,together with an enhanced PMA.We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain.A measure of the effective magnetic damping parameter(α_(eff)=0.04 ± 0.01) through a spin pumping experiment in a GdIG/Pt bilayer is also made.Through optimizing the growth dynamics of GdIG films,our results could be useful for synthesizing garnet films with a PMA,which could be beneficial for the future development of ferrimagnetic spintronics.     

A Rare 2D Framework Cu(atz)2 with Ferrimagnetic and High Proton Conductivity

Materials combining proton conductivity and magnetism have attracted great attention in recent years due to their intriguing application in sensors and fuel cells. Herein a two-dimensional metal-organic framework, [Cu(atz)₂(H₂O)₂]⋅H₂O ( 1 ) (Hatz=5-aminotetrazole), has been obtained in a green synthesis method. The single-crystal structure revealed that the atz⁻ ligands as linkers coordinate with copper ions to sql networks, between which water molecules are immobilized through hydrogen bonds. The resulting complex 1 exhibits a high proton conductivity of 1.11×10⁻⁴ and 6.19×10⁻⁴ S cm⁻¹ at room temperature and 333 K, respectively, under 98% RH with an activation energy of 0.56 eV. Upon dehydration, the proton conductivity of 1_dg drops by an order of magnitude. Furthermore, the magnetic behavior changes from long-range ferrimagnetic ordering of 1 to canted antiferromagnetic behaviour of 1_dg .