We present here measurements of the magnetization M, ac susceptibility χ ′ , electrical resistivity ρ, and specific heat C in single crystals of metallic YFe2Al10. The magnetic susceptibility follows a Curie-Weiss temperature dependence for 75 K≤T≤750 K, with a fluctuating Fe moment of 0.45 µB/Fe, and the ac susceptibility χ ′ diverges at lower temperatures χ ′ ∼T −1.28±0.04 when the ac field is in the basal plane. The field B and temperature T dependencies of the magnetization M are well described by the scaling expression MT −β =F(B/T β+γ ) for 1.8 K≤T≤30 K and for fields larger than 0.1 T. These results indicate that strong quasi-two dimensional critical fluctuations are present that can be suppressed by magnetic fields. The magnetic and electronic parts of the specific heat CM show a similar divergence for 0.4 K≤T≤12 K, where CM /T∼T −0.47±0.03 . The divergences in χ ′ and CM /T indicate that YFe2Al10 is located near a quantum critical point, and no magnetic order is observed above 0.09 K. We argue that our results are inconsistent with quantum impurity or disorder models, suggesting instead that YFe2Al10 is on the verge of bulk magnetic ordering, and that the critical fluctuations that are associated with this quantum critical point lead to the divergencies in CM /T and χ ′ .

We present measurements of the specific heat, magnetization, magnetocaloric effect and magnetic neutron diffraction carried out on single crystals of antiferromagnetic Yb3Pt4, where highly localized Yb moments order at TN = 2.4 K in zero field. The antiferromagnetic order was suppressed to TN → 0 by applying a field of 1.85 T in the ab plane. Magnetocaloric effect measurements show that the antiferromagnetic phase transition is always continuous for TN > 0, although a pronounced step in the magnetization is observed at the critical field in both neutron diffraction and magnetization measurements. These steps sharpen with decreasing temperature, but the related divergences in the magnetic susceptibility are cut off at the lowest temperatures, where the phase line itself becomes vertical in the field-temperature plane. As TN → 0, the antiferromagnetic transition is increasingly influenced by a quantum critical endpoint, where TN ultimately vanishes in a first order phase transition.