Possible Weak Ferromagnetism in Time Reversal Violating State of Underdoped Cuprates

Recent polar Kerr effect measurements on underdoped YBCO have provided evidence for time reversal symmetry breaking near the pseudogap temperature. These results are consistent wih the existance of a ferromagnetic moment of order 10\^{}(-4) Bohr magneton along the c-axis. We discuss the conditions for the possible occurrence of ferromagnetism with moments perpendicular to the Copper-Oxideplanes, accompanying the loop current orbital magnetic order, in the underdoped phase of Cuprates.