A theoretical study and realization of new spin quantum cross structure devices using organic materials

We have proposed a spin quantum cross structure (SQCS) device as a candidate beyond CMOS. The SQCS device consists of two ferromagnetic metal thin films with their edges crossed, and sandwiches a few atoms or molecules. In this work, the spin dependent transport formula has been derived for SQCS devices with collinear ferromagnetic electrodes within the framework of the Anderson Hamiltonian. Also, the calculation of the magnetoresistance (MR) ratio has been done as a function of renormalized transfer matrices including magnetostriction effects and the other effects phenomenologically. It is shown that the MR ratio can be controlled by changing the renormalized coupling constants. The MR ratio is represented by a new formula. Also, we have realized an SQCS device with Ni magnetic thin-film electrodes, sandwiching poly (3-hexylthiophene) (P3HT): 6, 6-phenyl-C61-butyric acid methyl ester (PCBM) organic molecules between both the electrodes. The current-voltage characteristics of SQCS devices were measured by a four-terminal method and agree well with the theoretical results, quantitatively

Large thermoelectric voltage in point contacts of Ni ferromagnetic metals

Recently, we have proposed a spin quantum cross structure (SQCS) device toward the realization of novel spintronics devices. In this paper, we have investigated thermoelectric effects in point contacts (PCs) of Ni ferromagnetic metals using SQCS devices, theoretically and experimentally. The calculated results show that the thermoelectric voltage Vq changes from 0.48 mV to 2.12 mV with the temperature difference of PCs increasing from 10 K to 50 K. Also, the magnitude of the theoretical thermoelectric voltage agrees very well with that of the experimental result. PCs of SQCS devices with Ni electrodes can serve as spin dependent thermobatteries

Theoretical investigation of new quantum-cross-structure device as a candidate beyond CMOS

We propose a new quantum cross structure (QCS) device as a candidate beyond CMOS. The QCS consists of two metal nano-ribbons having edge-to-edge configuration like crossed fins. The QCS has potential application in both switching devices and high-density memories by sandwiching a few molecules and atoms. The QCS can also have electrodes with different dimensional electron systems because we can change the widths, the lengths, and the heights of two metal nano-ribbons, respectively. Changing the dimensions of electron systems in both electrodes, we have calculated the current-voltage characteristics depending on the coupling constants between a molecule and the electrode. We find that the conductance peak is much sharper in case of weak coupling regardless of dimensions of electron systems in electrodes, compared to strong coupling case. We also find that the conductance peak of QCS having electrodes with two-dimensional electron systems (2DES) is much sharper than that of QCS having electrodes with three-dimensional electron systems (3DES) in case of strong coupling because of quantum size effect of 2DES. These results imply that the QCS with the very sharp conductance peak can serve as the devices to switch on and off by very small voltage change

Surface Roughness and Magnetic Properties of Ni and Ni78Fe22 Thin Films on Polyethylene Naphthalate Organic Substrates

We have studied structural, electrical, and magnetic properties of Ni and Ni78Fe22 thin films evaporated on polyethylene naphtalate (PEN) organic substrates towards the fabrication of spin quantum cross (SQC) devices. As we have investigated the scaling properties on the surface roughness, the surface roughness of Ni (16 nm)/PEN is 0.34 nm, corresponding to 2 or 3 atomic layers, in the scanning scale of 16 nm, and the surface roughness of Ni78Fe22 (14 nm)/PEN is also as small as 0.25 nm, corresponding to less than 2 atomic layers, in the scanning scale of 14 nm. These facts denote that Ni/PEN and Ni78Fe22/PEN are suitable for magnetic electrodes on organic substrates used for SQC devices from the viewpoint of the surface morphology. Then, we have investigated magnetic hysteresis curve and magnetoresistance effects for Ni/PEN and Ni78Fe22/PEN. The squareness of the hysteresis loop is as small as 0.24 for Ni (25 nm)/PEN, where there is no observation of the anisotropy magnetoresistance (AMR) effect. In contrast, the squareness of the hysteresis loop is as large as 0.86 for Ni78Fe22 (26 nm)/PEN, where the AMR effect has been successfully obtained. These experimental results indicate that Ni78Fe22/PEN is a promising material for use in SQC devices from the viewpoint of not only the surface morphologies but also magnetic properties

Theoretical and experimental results of electronic transport of spin quantum cross structure devices

Recently, we have proposed quantum cross structure (QCS) devices that consist of two metalthin films deposited on organic films with edge-to-edge configuration like crossed fins for switching devices. In this paper, we propose a spin quantum cross structure (SQCS) device, which is a QCS device consisting of two magnetic thin films. We show theoretical and experimental results of electronic transport characteristics regarding SQCS devices. The calculation of the I-Vcharacteristics has been performed for the SQCS devices with the Nimagnetic thin films for both the electrodes within the framework of the Anderson model. Then, we fabricated a SQCS device with the Nimagnetic thin films and measured the I-Vcharacteristics by a four-terminal method. Also, the calculation of the magnetoresistance ratio has been done as a function of renormalized transfer matrices including magnetostriction effects and the other effects phenomenologically

Surface morphologies and magnetic properties of Fe and Co magnetic thin films on polyethylene naphthalate organic substrates

We have studied the surface morphologies and magnetic properties of Fe and Co thin films evaporated on polyethylene naphthalate (PEN) organic substrates toward the fabrication of spin quantum cross devices. As a result, the surface roughnesses of Co (6.1 nm)/PEN and Co (12 nm)/PEN are as small as 0.1 and 0.09 nm, respectively, corresponding to less than one atomic layer, in the same scanning scale as the thickness. As for the magnetic properties, the coercive force of the Co/PEN shows the constant value of 2 kA/m upon decreasing the Co thickness from 35 to 10 nm, and it increases up to 7 kA/m upon decreasing the Co thickness from 10 to 5 nm. It decreases when the Co thickness is less than 5 nm. These results can be explained by the competition between the shape magnetic anisotropy and the induced magnetic anisotropy

Magnetic response of random lasing modes in a ZnO nanoparticle film deposited on a NiFe thin film

This study experimentally demonstrates lasing mode switching within a ZnO nanoparticle film coated onto a magnetic thin film of NiFe alloy. When a neodymium magnet is brought close to or moved away from the film, switching behavior is observed in the lasing modes, although such change is not induced in a ZnO nanoparticle film on a glass substrate. Our results suggest that the observed changes in lasing modes are because of a magneto-optical effect at the surface of the NiFe thin film. The magneto-optical effect would be enhanced by localized fields near the surface, inducing suppression or enhancement of the lasing modes in response to the surrounding environments, and accounting for the lasing mode switching

Wavelength-dependent magnetic transitions of self-organized iron-aluminum stripes induced by pulsed laser irradiation

We investigate the laser wavelength dependence of structural and magnetic transitions on the surface of an iron-aluminum (FeAl) alloy induced by nanosecond pulsed laser irradiation. The formation of self-organized FeAl stripes with a wavelength-dependent period is observed in a local area on the (111)-oriented plane. Focused magneto-optical Kerr effect measurements reveal that the coercivity reaches up to 1.2 kOe with increasing the magnetic field rotation angle, which is estimated from the stripe direction, in FeAl stripes irradiated at 355 nm, and its magnetization reversal can be explained by the domain-wall motion model. On the other hand, the magnetization reversal agrees with the Stoner-Wohlfarth model in FeAl stripes irradiated at 1064 nm. This magnetic transition originates from the B2-to-A2 phase transition in stripe structures and bulk regions. These results indicate that the magnetic transition from the incoherent to coherent mode as well as the structural transformation of stripe patterns can be controlled by the incident laser wavelength. (C) 2015 AIP Publishing LLC