and its Relationship to the Large Magnetoresistance*

Metallic 2D van der Waals materials that exhibit ferromagnetism (FM) are of considerable potential interest for spintronics applications because of the ability to manipulate their structure and properties. One such system is Cr₅Te₈ which consists of layers of CrTe₂ having additional Cr intercalated between the layers. CrTe₂ itself is known to be a strong ferromagnet up to room temperature [1].  Cr₅Te₈ is FM below T_c1=155K with perpendicular magnetic anisotropy and it exhibits a large (10%) negative magnetoresistance effect above T_c1 over a narrow temperature range [2].  

Detailed x-ray diffraction shows that the structure is C2/m with the possibility of two different crystallographic Cr sites within the intercalated Cr layer, which we confirm do not order in the FM phase.  Neutron Diffraction measurements were performed to explore its magnetic behavior in a temperature range above T_c1 and as a function of applied magnetic field.  A modulated antiferromagnetic phase is observed, which has a wavevector perpendicular to the van der Waals layers and a period that is triple the unit cell length.  The modulated spin structure is canted with a significant component in the van der Waals layers.  The modulation is robust with field applied in-plane but it is quickly destroyed with a field applied perpendicular to the layers.  Our magnetic phase diagram shows that the transition from FM to the modulated phase at T_c1 is strongly first-order with a true FM transition occurring at a higher temperature, T_c=180K.  We show that the large magnetoresistance observed in transport arises from the in-plane components of the magnetic moments.  Since the spin modulation is controlled at relatively low magnetic field and the intercalated Cr can be tuned, 2D systems such as these have potential for spintronic applications.

[1]    Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films X. Zhang et al., Nature Communications 12:2492 (2021)

[2]    Self-Intercalation Tunable Interlayer Exchange Coupling in a Synthetic Van der Waals Antiferromagnet X. Zhang et al., Advanced Functional Materials 2202977 (2022)