Pinning Energy of Domain Walls in MnZn Ferrite Films

VICTOR HUGO CALLE; FABIAN CUELLAR; CARLOS CALLE; OSCAR ALONSO MARIN RAMIREZ; JAIRO ROA ROJAS; DIEGO ARIAS; OCTAVIO GUZMAN; WILSON LOPERA; PEDRO PRIETO; ULRICH VOLKMANN; AMINTA MENDOZA

Santa Marta, Colombia

Workshop; Trends on Novel Materials; 2006

The multidomain structure of MnZn Ferrites film and its effects on the pinning energy of domain walls are investigated using Atomic Force Microscopy (AFM), Magneto Optical Kerr Effect (MOKE) and Vibrating Sample Magnetometer (VSM). MnZn Ferrite were deposited by RF sputtering technique on MgO substrates. The film thicknesses, ranging between 30 and 450 nm were determined by scanning electron microscopy (SEM). The AFM images show an increment in grain size as the film thicknesses increases. Grain diameter between f  70 – 700 nm have been observed. The coercive field Hc as a function of the grain size reaches a maximum value of 80 Oe for f  80 nm. This result indicates the existence of a multidomain structure associated with a critical grain size. That is when the size of the grain attains a value at which it becomes multidomain. We used a Jiles-Atherton model to discuss the experimental hysteresis loops. The Jiles-Atherton model is based in on domain walls motion, of an irreversible component due to wall displacement and a reversible component due to domain wall bending. The k pinning parameter of the model, k = dEloss/dM shows a maximum value of k/µ0 = 45 for grains with f 300 nm. Thus, above this f, the pinning has a minor effect on the wall displacement. Magnetic susceptibility measurement as a function of temperature indicates as increase in Curie temperature Tc with a maximum value of Tc=275 K for grains with f  300 nm. For grains with f  700 nm the Tc value was 228 K. The decreasing of Tc can be explained as the formation of multidomain structure indicated above.