Anisotropic quantum critical point in the Ce3Al system with a large magnetic anisotropy

A magnetic field driven quantum critical point (QCP) is studied experimentally in the Ce3Al magnetically anisotropic intermetallic compound, which shows both antiferromagnetic (AFM) ordering and heavy-fermion behavior. Measurements of the magnetic susceptibility, the magnetoresistance and the specific heat on a Ce3Al monocrystalline sample performed down to 0.35 K in magnetic fields up to 9 T demonstrate that the QCP is anisotropic regarding the orientation of the magnetic field relative to the magnetically easy direction. External magnetic field drives the AFM transition continuously toward zero temperature when applied in the (a, b) easy plane, reaching the QCP at the critical field B c a , b = 4.6 0.4 T, where a quantum phase transition from the AFM to the paramagnetic state takes place. The magnetoresistance experiments below 1 K indicate that intermediate magnetic states may have formed near the QCP. For the field applied along the c hard direction, the QCP has not been observed within our experimental range of the magnetic field. The anisotropic, magnetic field driven QCP in the Ce3Al results from competition of the exchange interaction with the Zeeman interaction in the presence of a large magnetocrystalline anisotropy. The anisotropy of the QCP is a consequence of the fact that the magnetic anisotropy locks the magnetization into the easy plane and cannot be pulled out of the plane by the available laboratory field. Consequently, only the component of the magnetic field vector that lies in the easy plane participates in the QCP formation. In AFM systems with a large magnetic anisotropy, the magnetic field driven QCP is a continuous variable of the magnetic field vector orientation relative to the easy direction.