Inverted hysteresis loops: Experimental artifacts arising from inappropriate or asymmetric sample positioning and the misinterpretation of experimental data

Inverted hysteresis loops (IHL) of negative net area have been measured for some films using vibrating sample magnetometer (VSM), SQUID magnetometer or magneto-optic Kerr effect magnetometer. All of the IHL were observed in the field direction along the hard axis. An IHL violates the thermo-mechanical second law. This work points out that an IHL arises when |Mx|≪|Mz||Mx|≪|Mz| (Mx and Mz: the parallel and normal to the field direction components of magnetization vector) if the sample is set at certain inappropriate positions in VSM and SQUID magnetometer experiments, and the sense voltage is solely attributed to Mx while it also relates to Mz.