The discovery of current-switchable bi-stable remanent domain configurations on small ferromagnetic islands is reported. Rectangular NiFe islands with a thickness of 50 to 100 nm and lateral dimensions on the order of several microns were imaged using magnetic force microscopy after application of 10 ns current pulses through the material. The closure configuration can be set into either the 4 or 7 domain configuration by applying positive or negative current polarity at density on the order 10 7 A/cm 2 . The chirality of the closure patterns is fixed, implying that only two rather than four states are stable in these patterns. The possibility of using these configurations as a means of storing a logic state for memory applications is discussed. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1495883͔The general method to assign a ''1'' or ''0'' in solid state magnetic memory devices is to orient the remanent magnetization of ferromagnetic elements in one of two opposite directions. Thus, the magnetic properties of small particles as well as new ways to switch the magnetization other than by applying an external magnetic field are topics of intense research activity. [1][2][3][4] In this letter, we offer an alternative approach to storing and reading binary information in magnetic systems. Specifically, we introduce the idea that a bi-stable remanent domain configuration of a ferromagnetic island, which is selectable by a current pulse through the material, can be a simple and viable option for magnetic random access memory applications.In a previous investigation, we established that in small rectangular NiFe thin film islands, the number of possible configurations at remanence (H applied ϭ0) is finite. 5 In the case where the length-to-width ratio ͑referred to as the aspect ratio͒ is between 1 and 4, and for thickness ϳ100 nm thin or less, the remanent states are predominantly 4-or 7-domain configurations. The four-domain ͑4D͒ structure is comprised of four 90°walls emanating from the corners and one 180°N éel wall at the center and parallel to the shape-induced easy axis. The seven-domain ͑7D͒ configuration, on the other hand, contains four 90°walls as in the previous case, but the 180°wall is replaced by a diamond-shaped domain at the center of the island, with an internal magnetization along the hard axis. These two states represent local minima of the energy and are determined by competition between the reduction of the magnetostatic energy and the cost of forming domain walls. From numerical calculations, the 7D configuration is about 25% lower in magnetostatic energy. We discovered that reversible 7D-4D state selection can be achieved by driving current pulses through the element in a process that involves domain wall displacement, 6 and submit that these two distinct domain configurations can be used to encode binary information.

We have performed experiments on current-induced domain-wall motion ͑CIDWM͒ in the case of the domain walls ͑DW͒ trapped within the nanoscale constrictions in patterned NiFe structures. Direct observation of current-induced magnetization reversal was achieved and critical current densities j c were measured in the presence of easy-axis magnetic fields. The direction of CIDWM was found to be along the direction of the electron motion in absence of an applied magnetic field and in the direction of the field when in the presence of even relatively weak fields. Data for the field dependence of j c for both uniform and fast rising pulses suggest that the current, regardless of polarity, assists in the depinning of the DW. Only for the dc case does the data strongly reveal the influence of the electron pressure in promoting or hindering DW motion.

Garnet films have been grown over (100)-oriented substituted gadolinium gallium garnet substrates partially populated with gold nanoparticles in order to study plasmon resonance enhancement of magneto-optic effects. The results of measurements of light transmission through these films as well as Faraday rotation are reported.

A new technique of magnetic imaging on a spin stand has been developed. In this technique, raw image acquisition is performed by scanning a target area of a disk by a conventional magneto-resistive (MR) read head in two orthogonal (along- and cross-track) directions. Due to the nonlocalized nature of the MR reading head in the cross-track direction, image reconstruction is needed in order to retrieve the actual distribution of magnetization. It is demonstrated that the image reconstruction can be performed by using the response function characterization of the MR head and the specially designed deconvolution technique, which yields the curl-free (field producing) component of magnetization. The technique developed is illustrated by the sample examples of imaging of overwritten tracks with small misregistrations.