I don't know where you read a patent on a PM electricity generator. In the US, it is prohibited by law from granting a patent on such a device.
A patent application contains one or more claims made by the inventor about why his invention is novel. The application does not require that the invention itself or a model be submitted for examination, so the claims are just that. The claims must meet certain statutory requirements. Patent requirements vary by country, so it is hard to generalize what is patentable and what is not without qualification.
Application of patents to intellectual property is recent and controversial. In the US, the courts have ruled through a series of precedents that abstract ideas, natural phenomena, and the laws of nature are not patentable. While discoveries can be patented in the US, they may not be patented in the EU.
Because of the imprecision of terms used in patent law and statutes, the field is rife with attorneys who specialize in knowing this field of the law. Because of the potential worth of some inventions, cases arising out of patent infringement can drag on for years sometimes. In the US, the Wright Bros. tried to enforce the patent on the their control system for the airplane, and early automobile manufacture was hampered somewhat when suits were brought against the manufacturers by holders of patents on early automobiles.
Due to the outbreak of World War I, the US government set up an aircraft manufacturers association which pooled the various aviation patents then current. All aircraft manufacturers were required to join the association and a token royalty payment was made to the various patent holders. Once the war ended, the association dissolved, but the various patent holders did not renew litigation.
In the case of the automobile patent case, most car makers decided to pay the patent holder his royalties in exchange for a license to use the patent to make cars. Henry Ford fought the patent in court and lost, but appealed his case and won in 1911. After that, car manufacture took off in the US, with Ford and General Motors quickly becoming the two largest car companies.