1. A MAGNETO-RESISTANCE NONRECIPROCAL SIGNAL AMPLIFIER COMPRISING IN COMBINATION, A BODY OF SEMICONDUCTOR MATERIAL HAVING SPACED ELECTRODAL SURFACE CONTACT ELEMENTS ARRANGED THEREON IN OPPOSED PAIRS ALONG TWO DIFFERENT AXES, MEANS FOR APPLYING A SIGNAL-VARIABLE UNIDIRECTIONAL MAGNETIC FIELD THROUGH SAID BODY ALONG A THIRD AXIS, MEANS CONNECTED WITH SAID PAIR OF CONTACT ELEMENS FOR APPLYING DIRECT-CURRENT VOLTAGES THERETO IN PREDETERMINED MAGNITUDE RELATION TO ESTABLISH ELECTRTICAL FIELDS IN SAID BODY AND A PREDETERMINED HIGH DEGREE OF SENSITIVE TO SAID