Besides their fundamental role as pinning layers in spintronic devices, antiferromagnetic materials are gaining interest by themselves thanks to the ability to store information in a magnetic state that is unaffected by external fields . The absence of a net magnetic moment, however, prevents any investigation of these materials through conventional magnetometric techniques. A possible route to probe antiferromagnetism electrically has been recently demonstrated in the Pt/Cr2O3 system by measuring the Anomalous Hall Effect arising from induced magnetization in Pt [2,3]. Here, using a similar approach, we present a combined study of resistivity, Hall and anomalous Hall in metallic antiferromagnetic thin films, proving a general method to assess antiferromagnetism which relies only on electrical measurements.
We first validate the technique by determining the Neèl temperature TN of IrMn thin films in a Ta(2 nm)/IrMn (4 nm)/Ta(2 nm)//SiO2 heterostructure grown by magnetron sputtering. We set a magnetic state by applying an out of plane field and cooling the sample below TN. Depending on the field cooling (FC) direction, a different Anomalous Hall Resistance (AHR) is observed below TN~100K. Underneath this temperature, the application of magnetic fields no longer affects the AHR signal, confirming its connection with the antiferromagnet state.
We follow the same approach to demonstrate antiferromagnetism also in epitaxial Chromium thin films grown on MgO. A small but clearly detectable AHR can be measured up to ~250 K for a Pt (3 nm)/Cr(50 nm)//MgO sample. Moreover, we will show the occurrence of the magnetic phase transition slightly over 250 K is further corroborated by anomalies in both resistivity and normal Hall coefficient, demonstrating unanbiguously antiferromagnetism in this system.
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