Impact of the Co Doping on the Structure, Magnetic Properties, and Phase Transition in Ni50-xCoxMn38Sn12 Ribbons

Three Heusler alloys, Ni50-xCoxMn38Sn12 (x = 1, 2, and 3), were elaborated by rapid solidification. The impact of the Co doping on the structure, magnetic properties, and phase transition in these alloys was studied. The structure of the Ni49Co1Mn38Sn12 and Ni48Co2Mn38Sn12 ribbons was martensite 14M monoclinic structure, while the Ni47Co3Mn38Sn12 sample structure was austenite cubic L21. The thermal analysis showed the impact of the substitution Ni by Co. It was noted that the temperatures of martensitic transition moved lower, and a decreases progressively of enthalpy and entropy changed. Likewise, an obvious increase in the temperature of Curie transition for austenite phase (TAC) was observed and a jump of magnetization change (ΔM) was detected, with increasing Cobalt content.

Photoinduced magnetic phase transition and remarkable enhancement of magnetization for a photochromic single-molecule magnet

A photochromic single-molecule magnet with large magnetization change (+20.9%) at room temperature and paramagnetic to ferromagnetic transition was successfully achieved.

Micromagnetic Simulations of Submicron Vortex Structures for the Detection of Superparamagnetic Labels

We present a numerical investigation on the detection of superparamagnetic labels using a giant magnetoresistance (GMR) vortex structure. For this purpose, the Landau–Lifshitz–Gilbert equation was solved numerically applying an external z-field for the activation of the superparamagnetic label. Initially, the free layer’s magnetization change due to the stray field of the label is simulated. The electric response of the GMR sensor is calculated by applying a self-consistent spin-diffusion model to the precomputed magnetization configurations. It is shown that the soft-magnetic free layer reacts on the stray field of the label by shifting the magnetic vortex orthogonally to the shift direction of the label. As a consequence, the electric potential of the GMR sensor changes significantly for label shifts parallel or antiparallel to the pinning of the fixed layer. Depending on the label size and its distance to the sensor, the GMR sensor responds, changing the electric potential from 26.6 mV to 28.3 mV.

A Low Frequency Mechanical Transmitter Based on Magnetoelectric Heterostructures Operated at Their Resonance Frequency

Magneto-elasto-electric (ME) coupling heterostructures, consisting of piezoelectric layers bonded to magnetostrictive ones, provide for a new class of electromagnetic emitter materials on which a portable (area ~ 16 cm2) very low frequency (VLF) transmitter technology could be developed. The proposed ME transmitter functions as follows: (a) a piezoelectric layer is first driven by alternating current AC electric voltage at its electromechanical resonance (EMR) frequency, (b) subsequently, this EMR excites the magnetostrictive layers, giving rise to magnetization change, (c) in turn, the magnetization oscillations result in oscillating magnetic fields. By Maxwell’s equations, a corresponding electric field, is also generated, leading to electromagnetic field propagation. Our hybrid piezoelectric-magnetostrictive transformer can take an input electric voltage that may include modulation-signal over a carrier frequency and transmit via oscillating magnetic field or flux change. The prototype measurements reveal a magnetic dipole like near field, demonstrating its transmission capabilities. Furthermore, the developed prototype showed a 104 times higher efficiency over a small-circular loop of the same area, exhibiting its superiority over the class of traditional small antennas.

MARTENSITIC TRANSFORMATION AND MAGNETIC PROPERTIES OF NiMnAl:Fe, Co FERROMAGNETIC SHAPE MEMORY ALLOYS

A series of Ni 50-x Fe x Mn 34 Al 16(0 ≦ x ≦ 18) and Ni 38 Fe 12-z Co z Mn 34 Al 16(3 ≦ z ≦ 6) ribbons were prepared by the melt-spinning method. With Fe substitution for Ni in Ni 50 Mn 34 Al 16 ribbons, the magnetization of the austenitic phase increases greatly while that of the martensitic phase increases little. Thus, in the magnetic field of 5 T a large magnetization change (22 Am2/kg) during the martensitic transformation is observed in Ni 38 Fe 12 Mn 34 Al 16 ribbon. The effect of Fe substitution for Ni on the magnetic modulation was investigated, which is attributed to the change of the magnetic interaction between Mn – Mn atoms. By substituting Co for Fe in Ni 38 Fe 12 Mn 34 Al 16 ribbons, a magnetic-field-induced martensite-austenite transformation is observed in Ni 38 Fe 9 Co 3 Mn 34 Al 16 ribbon.