Magnetic thermal hysteresis in Co/ Gd, CoNi/ Gd, and Fe/ Gd multilayers is investigated by measurements of the total magnetic moment. A measurement of the magnetization as a function of temperature for the antiferromagnetically coupled multilayers displays a characteristic bow-tie shape indicating magnetic superheating and supercooling. The width of the thermal hysteresis can be tuned by an external magnetic field, with values of 150 K at fields near 100 Oe and values of 20 K near 400 Oe. The results are in good agreement with our theoretical calculations.

We show that tunable magnetic thermal hysteresis can be realized for a simple ferrimagnetic CoGd alloy. The magnetization of a Co0.8Gd0.2 alloy shows a bow-tie curve as a function of temperature, which indicates supercooled and superheated phase transitions. The width of the magnetic thermal hysteresis can be tuned by an external magnetic field, with values of 190 K at fields near 100 Oe and values of 20 K near 400 Oe. Experimental results are in reasonable agreement with theoretical calculations.

We investigate the coercivity and exchange bias effect in Fe/Gd multilayers. Antiferromagnetically coupled (Fe 4 nm/Gd 4 nm)4 multilayer has a compensation temperature (Tcomp) of approximately 90 K. We observe that the coercivity of the inhomogeneous Fe/Gd ferrimagnet makes a local minimum near the Tcomp. When a 16-nm-thick Gd layer is deposited over a (Fe 4 nm/Gd 4 nm)4 multilayer, exchange bias emerges due to the interfacial interaction of the thick Gd overlayer and the Fe surface of the multilayer. Negative and positive exchange bias were observed below and above the Tcomp, respectively. In addition, there is a continuous transition from negative exchange bias to positive exchange bias across the Tcomp where coercivity makes the local minimum.

Articles you may be interested inVisualization of vortex motion in FeAs-based BaFe1.9Ni0.1As2 single crystal by means of magneto-optical imagingWe report on optimizing the magneto-optical ͑MO͒ response of dielectric/Fe/dielectric sandwich structures for microwave B-field sensor applications. We have performed experimental MO spectroscopic and simulation studies of FeF 2 / Fe/ FeF 2 sandwiches with varying both top and bottom FeF 2 layer thicknesses. We evaluate the performance of the sensor with MO figure of merit ͑off-diagonal reflection coefficient͒ rather than with MO polarization state ͑MO azimuth rotation and ellipticity͒. Our simulations indicate that an increase in the modulus of the MO signal by a factor of 17 is feasible compared to the bulk Fe. However, the corresponding enhancement of the figure of merit, which is the relevant parameter, is only threefold. These simulations were carried out for the operating wavelength of sensors at 810 nm. We show, contrary to the general belief, that in order to enhance the MO performance of the sensor it is more important to optimize the bottom dielectric layer rather than the top layer.

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